[PATCH v11 bpf-next 0/7] Enable writing xattr from BPF programs

[PATCH v11 bpf-next 0/7] Enable writing xattr from BPF programs

[Song Liu]

Add support to set and remove xattr from BPF program. Also add
security.bpf. xattr name prefix.

kfuncs are added to set and remove xattrs with security.bpf. name
prefix. Update kfuncs bpf_get_[file|dentry]_xattr to read xattrs
with security.bpf. name prefix. Note that BPF programs can read
user. xattrs, but not write and remove them.

To pick the right version of kfunc to use, a remap logic is added to
btf_kfunc_id_set. This helps move some kfunc specific logic off the
verifier core code. Also use this remap logic to select
bpf_dynptr_from_skb or bpf_dynptr_from_skb_rdonly.


Cover letter of v1 and v2:

Follow up discussion in LPC 2024 [1], that we need security.bpf xattr
prefix. This set adds "security.bpf." xattr name prefix, and allows
bpf kfuncs bpf_get_[file|dentry]_xattr() to read these xattrs.

[1] https://lpc.events/event/18/contributions/1940/

---

Changes v10 => v11:

1. Add Acked-by from Christian Brauner.
2. Fix selftests build error like this one:
   https://github.com/kernel-patches/bpf/actions/runs/13022268618/job/36325472992
3. Rename some variables in the selftests.

v10: https://lore.kernel.org/bpf/20250124202911.3264715-1-song@kernel.org/

Changes v9 => v10:
1. Refactor bpf_[set|remove]_dentry_xattr[_locked]. (Christian Brauner).

v9: https://lore.kernel.org/bpf/20250110011342.2965136-1-song@kernel.org/

Changes v8 => v9
1. Fix build for CONFIG_DEBUG_INFO_BTF=n case. (kernel test robot)

v8: https://lore.kernel.org/bpf/20250108225140.3467654-1-song@kernel.org/

Changes v7 => v8
1. Rebase and resolve conflicts.

v7: https://lore.kernel.org/bpf/20241219221439.2455664-1-song@kernel.org/

Changes v6 => v7
1. Move btf_kfunc_id_remap() to the right place. (Bug reported by CI)

v6: https://lore.kernel.org/bpf/20241219202536.1625216-1-song@kernel.org/

Changes v5 => v6
1. Hide _locked version of the kfuncs from vmlinux.h (Alexei)
2. Add remap logic to btf_kfunc_id_set and use that to pick the correct
   version of kfuncs to use.
3. Also use the remap logic for bpf_dynptr_from_skb[|_rdonly].

v5: https://lore.kernel.org/bpf/20241218044711.1723221-1-song@kernel.org/

Changes v4 => v5
1. Let verifier pick proper kfunc (_locked or not _locked)  based on the
   calling context. (Alexei)
2. Remove the __failure test (6/6 of v4).

v4: https://lore.kernel.org/bpf/20241217063821.482857-1-song@kernel.org/

Changes v3 => v4
1. Do write permission check with inode locked. (Jan Kara)
2. Fix some source_inline warnings.

v3: https://lore.kernel.org/bpf/20241210220627.2800362-1-song@kernel.org/

Changes v2 => v3
1. Add kfuncs to set and remove xattr from BPF programs.

v2: https://lore.kernel.org/bpf/20241016070955.375923-1-song@kernel.org/

Changes v1 => v2
1. Update comment of bpf_get_[file|dentry]_xattr. (Jiri Olsa)
2. Fix comment for return value of bpf_get_[file|dentry]_xattr.

v1: https://lore.kernel.org/bpf/20241002214637.3625277-1-song@kernel.org/

Song Liu (7):
  fs/xattr: bpf: Introduce security.bpf. xattr name prefix
  selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr
    names
  bpf: lsm: Add two more sleepable hooks
  bpf: Extend btf_kfunc_id_set to handle kfunc polymorphism
  bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb
  bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs
  selftests/bpf: Test kfuncs that set and remove xattr from BPF programs

 fs/bpf_fs_kfuncs.c                            | 238 +++++++++++++++++-
 include/linux/bpf_lsm.h                       |   2 +
 include/linux/btf.h                           |  20 ++
 include/linux/btf_ids.h                       |   4 +
 include/uapi/linux/xattr.h                    |   4 +
 kernel/bpf/bpf_lsm.c                          |   2 +
 kernel/bpf/btf.c                              | 117 +++++++--
 kernel/bpf/verifier.c                         |  31 +--
 net/core/filter.c                             |  49 +++-
 tools/testing/selftests/bpf/bpf_kfuncs.h      |   5 +
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 162 +++++++++++-
 .../selftests/bpf/progs/test_get_xattr.c      |  28 ++-
 .../bpf/progs/test_set_remove_xattr.c         | 133 ++++++++++
 13 files changed, 732 insertions(+), 63 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_set_remove_xattr.c

--
2.43.5

[PATCH v11 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

[Song Liu]

Introduct new xattr name prefix security.bpf., and enable reading these
xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr().

As we are on it, correct the comments for return value of
bpf_get_[file|dentry]_xattr(), i.e. return length the xattr value on
success.

Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/bpf_fs_kfuncs.c         | 19 ++++++++++++++-----
 include/uapi/linux/xattr.h |  4 ++++
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 3fe9f59ef867..8a65184c8c2c 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -93,6 +93,11 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
 	return len;
 }
 
+static bool match_security_bpf_prefix(const char *name__str)
+{
+	return !strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN);
+}
+
 /**
  * bpf_get_dentry_xattr - get xattr of a dentry
  * @dentry: dentry to get xattr from
@@ -101,9 +106,10 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
  *
  * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
  *
- * For security reasons, only *name__str* with prefix "user." is allowed.
+ * For security reasons, only *name__str* with prefix "user." or
+ * "security.bpf." is allowed.
  *
- * Return: 0 on success, a negative value on error.
+ * Return: length of the xattr value on success, a negative value on error.
  */
 __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
 				     struct bpf_dynptr *value_p)
@@ -117,7 +123,9 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
 	if (WARN_ON(!inode))
 		return -EINVAL;
 
-	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
+	/* Allow reading xattr with user. and security.bpf. prefix */
+	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
+	    !match_security_bpf_prefix(name__str))
 		return -EPERM;
 
 	value_len = __bpf_dynptr_size(value_ptr);
@@ -139,9 +147,10 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
  *
  * Get xattr *name__str* of *file* and store the output in *value_ptr*.
  *
- * For security reasons, only *name__str* with prefix "user." is allowed.
+ * For security reasons, only *name__str* with prefix "user." or
+ * "security.bpf." is allowed.
  *
- * Return: 0 on success, a negative value on error.
+ * Return: length of the xattr value on success, a negative value on error.
  */
 __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
 				   struct bpf_dynptr *value_p)
diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
index 9854f9cff3c6..c7c85bb504ba 100644
--- a/include/uapi/linux/xattr.h
+++ b/include/uapi/linux/xattr.h
@@ -83,6 +83,10 @@ struct xattr_args {
 #define XATTR_CAPS_SUFFIX "capability"
 #define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX
 
+#define XATTR_BPF_LSM_SUFFIX "bpf."
+#define XATTR_NAME_BPF_LSM (XATTR_SECURITY_PREFIX XATTR_BPF_LSM_SUFFIX)
+#define XATTR_NAME_BPF_LSM_LEN (sizeof(XATTR_NAME_BPF_LSM) - 1)
+
 #define XATTR_POSIX_ACL_ACCESS  "posix_acl_access"
 #define XATTR_NAME_POSIX_ACL_ACCESS XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_ACCESS
 #define XATTR_POSIX_ACL_DEFAULT  "posix_acl_default"
-- 
2.43.5

[PATCH v11 bpf-next 2/7] selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names

[Song Liu]

Extend test_progs fs_kfuncs to cover different xattr names. Specifically:
xattr name "user.kfuncs" and "security.bpf.xxx" can be read from BPF
program with kfuncs bpf_get_[file|dentry]_xattr(); while "security.bpf"
and "security.selinux" cannot be read.

Signed-off-by: Song Liu <song@kernel.org>
---
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 37 ++++++++++++++-----
 .../selftests/bpf/progs/test_get_xattr.c      | 28 ++++++++++++--
 2 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 5a0b51157451..419f45b56472 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -12,7 +12,7 @@
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
 
-static void test_xattr(void)
+static void test_get_xattr(const char *name, const char *value, bool allow_access)
 {
 	struct test_get_xattr *skel = NULL;
 	int fd = -1, err;
@@ -25,7 +25,7 @@ static void test_xattr(void)
 	close(fd);
 	fd = -1;
 
-	err = setxattr(testfile, "user.kfuncs", "hello", sizeof("hello"), 0);
+	err = setxattr(testfile, name, value, strlen(value) + 1, 0);
 	if (err && errno == EOPNOTSUPP) {
 		printf("%s:SKIP:local fs doesn't support xattr (%d)\n"
 		       "To run this test, make sure /tmp filesystem supports xattr.\n",
@@ -48,16 +48,23 @@ static void test_xattr(void)
 		goto out;
 
 	fd = open(testfile, O_RDONLY, 0644);
+
 	if (!ASSERT_GE(fd, 0, "open_file"))
 		goto out;
 
-	ASSERT_EQ(skel->bss->found_xattr_from_file, 1, "found_xattr_from_file");
-
 	/* Trigger security_inode_getxattr */
-	err = getxattr(testfile, "user.kfuncs", v, sizeof(v));
-	ASSERT_EQ(err, -1, "getxattr_return");
-	ASSERT_EQ(errno, EINVAL, "getxattr_errno");
-	ASSERT_EQ(skel->bss->found_xattr_from_dentry, 1, "found_xattr_from_dentry");
+	err = getxattr(testfile, name, v, sizeof(v));
+
+	if (allow_access) {
+		ASSERT_EQ(err, -1, "getxattr_return");
+		ASSERT_EQ(errno, EINVAL, "getxattr_errno");
+		ASSERT_EQ(skel->bss->found_xattr_from_file, 1, "found_xattr_from_file");
+		ASSERT_EQ(skel->bss->found_xattr_from_dentry, 1, "found_xattr_from_dentry");
+	} else {
+		ASSERT_EQ(err, strlen(value) + 1, "getxattr_return");
+		ASSERT_EQ(skel->bss->found_xattr_from_file, 0, "found_xattr_from_file");
+		ASSERT_EQ(skel->bss->found_xattr_from_dentry, 0, "found_xattr_from_dentry");
+	}
 
 out:
 	close(fd);
@@ -141,8 +148,18 @@ static void test_fsverity(void)
 
 void test_fs_kfuncs(void)
 {
-	if (test__start_subtest("xattr"))
-		test_xattr();
+	/* Matches xattr_names in progs/test_get_xattr.c */
+	if (test__start_subtest("user_xattr"))
+		test_get_xattr("user.kfuncs", "hello", true);
+
+	if (test__start_subtest("security_bpf_xattr"))
+		test_get_xattr("security.bpf.xxx", "hello", true);
+
+	if (test__start_subtest("security_bpf_xattr_error"))
+		test_get_xattr("security.bpf", "hello", false);
+
+	if (test__start_subtest("security_selinux_xattr_error"))
+		test_get_xattr("security.selinux", "hello", false);
 
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
diff --git a/tools/testing/selftests/bpf/progs/test_get_xattr.c b/tools/testing/selftests/bpf/progs/test_get_xattr.c
index 66e737720f7c..54305f4c9f2d 100644
--- a/tools/testing/selftests/bpf/progs/test_get_xattr.c
+++ b/tools/testing/selftests/bpf/progs/test_get_xattr.c
@@ -6,6 +6,7 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include "bpf_kfuncs.h"
+#include "bpf_misc.h"
 
 char _license[] SEC("license") = "GPL";
 
@@ -17,12 +18,23 @@ static const char expected_value[] = "hello";
 char value1[32];
 char value2[32];
 
+/* Matches caller of test_get_xattr() in prog_tests/fs_kfuncs.c */
+static const char xattr_names[][64] = {
+	/* The following work. */
+	"user.kfuncs",
+	"security.bpf.xxx",
+
+	/* The following do not work. */
+	"security.bpf",
+	"security.selinux"
+};
+
 SEC("lsm.s/file_open")
 int BPF_PROG(test_file_open, struct file *f)
 {
 	struct bpf_dynptr value_ptr;
 	__u32 pid;
-	int ret;
+	int ret, i;
 
 	pid = bpf_get_current_pid_tgid() >> 32;
 	if (pid != monitored_pid)
@@ -30,7 +42,11 @@ int BPF_PROG(test_file_open, struct file *f)
 
 	bpf_dynptr_from_mem(value1, sizeof(value1), 0, &value_ptr);
 
-	ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
+	for (i = 0; i < ARRAY_SIZE(xattr_names); i++) {
+		ret = bpf_get_file_xattr(f, xattr_names[i], &value_ptr);
+		if (ret == sizeof(expected_value))
+			break;
+	}
 	if (ret != sizeof(expected_value))
 		return 0;
 	if (bpf_strncmp(value1, ret, expected_value))
@@ -44,7 +60,7 @@ int BPF_PROG(test_inode_getxattr, struct dentry *dentry, char *name)
 {
 	struct bpf_dynptr value_ptr;
 	__u32 pid;
-	int ret;
+	int ret, i;
 
 	pid = bpf_get_current_pid_tgid() >> 32;
 	if (pid != monitored_pid)
@@ -52,7 +68,11 @@ int BPF_PROG(test_inode_getxattr, struct dentry *dentry, char *name)
 
 	bpf_dynptr_from_mem(value2, sizeof(value2), 0, &value_ptr);
 
-	ret = bpf_get_dentry_xattr(dentry, "user.kfuncs", &value_ptr);
+	for (i = 0; i < ARRAY_SIZE(xattr_names); i++) {
+		ret = bpf_get_dentry_xattr(dentry, xattr_names[i], &value_ptr);
+		if (ret == sizeof(expected_value))
+			break;
+	}
 	if (ret != sizeof(expected_value))
 		return 0;
 	if (bpf_strncmp(value2, ret, expected_value))
-- 
2.43.5

[PATCH v11 bpf-next 3/7] bpf: lsm: Add two more sleepable hooks

[Song Liu]

Add bpf_lsm_inode_removexattr and bpf_lsm_inode_post_removexattr to list
sleepable_lsm_hooks. These two hooks are always called from sleepable
context.

Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/bpf/bpf_lsm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 967492b65185..0a59df1c550a 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -316,7 +316,9 @@ BTF_ID(func, bpf_lsm_inode_getxattr)
 BTF_ID(func, bpf_lsm_inode_mknod)
 BTF_ID(func, bpf_lsm_inode_need_killpriv)
 BTF_ID(func, bpf_lsm_inode_post_setxattr)
+BTF_ID(func, bpf_lsm_inode_post_removexattr)
 BTF_ID(func, bpf_lsm_inode_readlink)
+BTF_ID(func, bpf_lsm_inode_removexattr)
 BTF_ID(func, bpf_lsm_inode_rename)
 BTF_ID(func, bpf_lsm_inode_rmdir)
 BTF_ID(func, bpf_lsm_inode_setattr)
-- 
2.43.5

[PATCH v11 bpf-next 4/7] bpf: Extend btf_kfunc_id_set to handle kfunc polymorphism

[Song Liu]

Polymorphism exists in kernel functions, BPF helpers, as well as kfuncs.
When called from different contexts, it is necessary to pick the right
version of a kfunc. One of such example is bpf_dynptr_from_skb vs.
bpf_dynptr_from_skb_rdonly.

To avoid the burden on the users, the verifier can inspect the calling
context and select the right version of kfunc. However, with more kfuncs
being added to the kernel, it is not scalable to push all these logic
to the verifiler.

Extend btf_kfunc_id_set to handle kfunc polymorphism. Specifically,
a list of kfuncs, "hidden_set", and a new method "remap" is added to
btf_kfunc_id_set. kfuncs in hidden_set do not have BTF_SET8_KFUNCS flag,
and are not exposed in vmlinux.h. The remap method is used to inspect
the calling context, and when necessary, remap the user visible kfuncs
(for example, bpf_dynptr_from_skb), to its hidden version (for example,
bpf_dynptr_from_skb_rdonly).

The verifier calls in these remap logic via the new btf_kfunc_id_remap()
API, and picks the right kfuncs for the context.

Signed-off-by: Song Liu <song@kernel.org>
---
 include/linux/btf.h     |  20 +++++++
 include/linux/btf_ids.h |   4 ++
 kernel/bpf/btf.c        | 117 ++++++++++++++++++++++++++++++++++------
 kernel/bpf/verifier.c   |   6 ++-
 4 files changed, 128 insertions(+), 19 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index 2a08a2b55592..065c374c4372 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -114,11 +114,23 @@ struct btf_id_set;
 struct bpf_prog;
 
 typedef int (*btf_kfunc_filter_t)(const struct bpf_prog *prog, u32 kfunc_id);
+typedef u32 (*btf_kfunc_remap_t)(const struct bpf_prog *prog, u32 kfunc_id);
 
 struct btf_kfunc_id_set {
 	struct module *owner;
 	struct btf_id_set8 *set;
+
+	/* *hidden_set* contains kfuncs that are not exposed as kfunc in
+	 * vmlinux.h. These kfuncs are usually a variation of a kfunc
+	 * in *set*.
+	 */
+	struct btf_id_set8 *hidden_set;
 	btf_kfunc_filter_t filter;
+
+	/* *remap* method remaps kfuncs in *set* to proper version in
+	 * *hidden_set*.
+	 */
+	btf_kfunc_remap_t remap;
 };
 
 struct btf_id_dtor_kfunc {
@@ -575,6 +587,8 @@ u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id,
 int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
 			      const struct btf_kfunc_id_set *s);
 int register_btf_fmodret_id_set(const struct btf_kfunc_id_set *kset);
+u32 btf_kfunc_id_remap(const struct btf *btf, u32 kfunc_btf_id,
+		       const struct bpf_prog *prog);
 s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id);
 int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_cnt,
 				struct module *owner);
@@ -637,6 +651,12 @@ static inline u32 *btf_kfunc_id_set_contains(const struct btf *btf,
 {
 	return NULL;
 }
+static inline u32 btf_kfunc_id_remap(const struct btf *btf, u32 kfunc_btf_id,
+				     const struct bpf_prog *prog)
+{
+	return kfunc_btf_id;
+}
+
 static inline int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
 					    const struct btf_kfunc_id_set *s)
 {
diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 139bdececdcf..0744b84e64a9 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h
@@ -212,6 +212,9 @@ extern struct btf_id_set8 name;
 #define BTF_KFUNCS_START(name)				\
 __BTF_SET8_START(name, local, BTF_SET8_KFUNCS)
 
+#define BTF_HIDDEN_KFUNCS_START(name)			\
+__BTF_SET8_START(name, local, 0)
+
 #define BTF_KFUNCS_END(name)				\
 BTF_SET8_END(name)
 
@@ -230,6 +233,7 @@ BTF_SET8_END(name)
 #define BTF_SET8_START(name) static struct btf_id_set8 __maybe_unused name = { 0 };
 #define BTF_SET8_END(name)
 #define BTF_KFUNCS_START(name) static struct btf_id_set8 __maybe_unused name = { .flags = BTF_SET8_KFUNCS };
+#define BTF_HIDDEN_KFUNCS_START(name) static struct btf_id_set8 __maybe_unused name = { .flags = BTF_SET8_KFUNCS };
 #define BTF_KFUNCS_END(name)
 
 #endif /* CONFIG_DEBUG_INFO_BTF */
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 8396ce1d0fba..0ffe99205e9c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -226,6 +226,7 @@ enum {
 	BTF_KFUNC_SET_MAX_CNT = 256,
 	BTF_DTOR_KFUNC_MAX_CNT = 256,
 	BTF_KFUNC_FILTER_MAX_CNT = 16,
+	BTF_KFUNC_REMAP_MAX_CNT = 16,
 };
 
 struct btf_kfunc_hook_filter {
@@ -233,9 +234,15 @@ struct btf_kfunc_hook_filter {
 	u32 nr_filters;
 };
 
+struct btf_kfunc_hook_remap {
+	btf_kfunc_remap_t remaps[BTF_KFUNC_REMAP_MAX_CNT];
+	u32 nr_remaps;
+};
+
 struct btf_kfunc_set_tab {
 	struct btf_id_set8 *sets[BTF_KFUNC_HOOK_MAX];
 	struct btf_kfunc_hook_filter hook_filters[BTF_KFUNC_HOOK_MAX];
+	struct btf_kfunc_hook_remap hook_remaps[BTF_KFUNC_HOOK_MAX];
 };
 
 struct btf_id_dtor_kfunc_tab {
@@ -8372,16 +8379,35 @@ static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags)
 
 /* Kernel Function (kfunc) BTF ID set registration API */
 
+static void btf_add_kfunc_to_set(struct btf *btf, struct btf_id_set8 *set,
+				 struct btf_id_set8 *add_set)
+{
+	u32 i;
+
+	if (!add_set)
+		return;
+	/* Concatenate the two sets */
+	memcpy(set->pairs + set->cnt, add_set->pairs, add_set->cnt * sizeof(set->pairs[0]));
+	/* Now that the set is copied, update with relocated BTF ids */
+	for (i = set->cnt; i < set->cnt + add_set->cnt; i++)
+		set->pairs[i].id = btf_relocate_id(btf, set->pairs[i].id);
+
+	set->cnt += add_set->cnt;
+
+	sort(set->pairs, set->cnt, sizeof(set->pairs[0]), btf_id_cmp_func, NULL);
+}
+
 static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 				  const struct btf_kfunc_id_set *kset)
 {
 	struct btf_kfunc_hook_filter *hook_filter;
-	struct btf_id_set8 *add_set = kset->set;
+	struct btf_kfunc_hook_remap *hook_remap;
 	bool vmlinux_set = !btf_is_module(btf);
 	bool add_filter = !!kset->filter;
+	bool add_remap = !!kset->remap;
 	struct btf_kfunc_set_tab *tab;
 	struct btf_id_set8 *set;
-	u32 set_cnt, i;
+	u32 set_cnt, add_cnt, i;
 	int ret;
 
 	if (hook >= BTF_KFUNC_HOOK_MAX) {
@@ -8389,14 +8415,16 @@ static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 		goto end;
 	}
 
-	if (!add_set->cnt)
+	add_cnt = kset->set->cnt;
+	if (kset->hidden_set)
+		add_cnt += kset->hidden_set->cnt;
+
+	if (!add_cnt)
 		return 0;
 
 	tab = btf->kfunc_set_tab;
 
 	if (tab && add_filter) {
-		u32 i;
-
 		hook_filter = &tab->hook_filters[hook];
 		for (i = 0; i < hook_filter->nr_filters; i++) {
 			if (hook_filter->filters[i] == kset->filter) {
@@ -8411,6 +8439,21 @@ static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 		}
 	}
 
+	if (tab && add_remap) {
+		hook_remap = &tab->hook_remaps[hook];
+		for (i = 0; i < hook_remap->nr_remaps; i++) {
+			if (hook_remap->remaps[i] == kset->remap) {
+				add_remap = false;
+				break;
+			}
+		}
+
+		if (add_remap && hook_remap->nr_remaps == BTF_KFUNC_REMAP_MAX_CNT) {
+			ret = -E2BIG;
+			goto end;
+		}
+	}
+
 	if (!tab) {
 		tab = kzalloc(sizeof(*tab), GFP_KERNEL | __GFP_NOWARN);
 		if (!tab)
@@ -8439,19 +8482,19 @@ static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 	 */
 	set_cnt = set ? set->cnt : 0;
 
-	if (set_cnt > U32_MAX - add_set->cnt) {
+	if (set_cnt > U32_MAX - add_cnt) {
 		ret = -EOVERFLOW;
 		goto end;
 	}
 
-	if (set_cnt + add_set->cnt > BTF_KFUNC_SET_MAX_CNT) {
+	if (set_cnt + add_cnt > BTF_KFUNC_SET_MAX_CNT) {
 		ret = -E2BIG;
 		goto end;
 	}
 
 	/* Grow set */
 	set = krealloc(tab->sets[hook],
-		       offsetof(struct btf_id_set8, pairs[set_cnt + add_set->cnt]),
+		       offsetof(struct btf_id_set8, pairs[set_cnt + add_cnt]),
 		       GFP_KERNEL | __GFP_NOWARN);
 	if (!set) {
 		ret = -ENOMEM;
@@ -8463,20 +8506,18 @@ static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 		set->cnt = 0;
 	tab->sets[hook] = set;
 
-	/* Concatenate the two sets */
-	memcpy(set->pairs + set->cnt, add_set->pairs, add_set->cnt * sizeof(set->pairs[0]));
-	/* Now that the set is copied, update with relocated BTF ids */
-	for (i = set->cnt; i < set->cnt + add_set->cnt; i++)
-		set->pairs[i].id = btf_relocate_id(btf, set->pairs[i].id);
-
-	set->cnt += add_set->cnt;
-
-	sort(set->pairs, set->cnt, sizeof(set->pairs[0]), btf_id_cmp_func, NULL);
+	btf_add_kfunc_to_set(btf, set, kset->set);
+	btf_add_kfunc_to_set(btf, set, kset->hidden_set);
 
 	if (add_filter) {
 		hook_filter = &tab->hook_filters[hook];
 		hook_filter->filters[hook_filter->nr_filters++] = kset->filter;
 	}
+
+	if (add_remap) {
+		hook_remap = &tab->hook_remaps[hook];
+		hook_remap->remaps[hook_remap->nr_remaps++] = kset->remap;
+	}
 	return 0;
 end:
 	btf_free_kfunc_set_tab(btf);
@@ -8511,6 +8552,28 @@ static u32 *__btf_kfunc_id_set_contains(const struct btf *btf,
 	return id + 1;
 }
 
+static u32 __btf_kfunc_id_remap(const struct btf *btf,
+				enum btf_kfunc_hook hook,
+				u32 kfunc_btf_id,
+				const struct bpf_prog *prog)
+{
+	struct btf_kfunc_hook_remap *hook_remap;
+	u32 i, remap_id = 0;
+
+	if (hook >= BTF_KFUNC_HOOK_MAX)
+		return 0;
+	if (!btf->kfunc_set_tab)
+		return 0;
+	hook_remap = &btf->kfunc_set_tab->hook_remaps[hook];
+
+	for (i = 0; i < hook_remap->nr_remaps; i++) {
+		remap_id = hook_remap->remaps[i](prog, kfunc_btf_id);
+		if (remap_id)
+			break;
+	}
+	return remap_id;
+}
+
 static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
 {
 	switch (prog_type) {
@@ -8579,6 +8642,26 @@ u32 *btf_kfunc_id_set_contains(const struct btf *btf,
 	return __btf_kfunc_id_set_contains(btf, hook, kfunc_btf_id, prog);
 }
 
+/* Reference to the module (obtained using btf_try_get_module)
+ * corresponding to the struct btf *MUST* be held when calling this
+ * function from the verifier
+ */
+u32 btf_kfunc_id_remap(const struct btf *btf, u32 kfunc_btf_id,
+		       const struct bpf_prog *prog)
+{
+	enum bpf_prog_type prog_type = resolve_prog_type(prog);
+	enum btf_kfunc_hook hook;
+	u32 remap_id;
+
+	remap_id = __btf_kfunc_id_remap(btf, BTF_KFUNC_HOOK_COMMON, kfunc_btf_id, prog);
+	if (remap_id)
+		return remap_id;
+
+	hook = bpf_prog_type_to_kfunc_hook(prog_type);
+	remap_id = __btf_kfunc_id_remap(btf, hook, kfunc_btf_id, prog);
+	return remap_id ?: kfunc_btf_id;
+}
+
 u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id,
 				const struct bpf_prog *prog)
 {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03adfd5..2188b6674266 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3030,13 +3030,14 @@ static struct btf *find_kfunc_desc_btf(struct bpf_verifier_env *env, s16 offset)
 	return btf_vmlinux ?: ERR_PTR(-ENOENT);
 }
 
-static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
+static int add_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, s16 offset)
 {
 	const struct btf_type *func, *func_proto;
 	struct bpf_kfunc_btf_tab *btf_tab;
 	struct bpf_kfunc_desc_tab *tab;
 	struct bpf_prog_aux *prog_aux;
 	struct bpf_kfunc_desc *desc;
+	u32 func_id = insn->imm;
 	const char *func_name;
 	struct btf *desc_btf;
 	unsigned long call_imm;
@@ -3095,6 +3096,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 		return PTR_ERR(desc_btf);
 	}
 
+	func_id = insn->imm = btf_kfunc_id_remap(desc_btf, insn->imm, env->prog);
 	if (find_kfunc_desc(env->prog, func_id, offset))
 		return 0;
 
@@ -3228,7 +3230,7 @@ static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
 		if (bpf_pseudo_func(insn) || bpf_pseudo_call(insn))
 			ret = add_subprog(env, i + insn->imm + 1);
 		else
-			ret = add_kfunc_call(env, insn->imm, insn->off);
+			ret = add_kfunc_call(env, insn, insn->off);
 
 		if (ret < 0)
 			return ret;
-- 
2.43.5

[PATCH v11 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Song Liu]

btf_kfunc_id_set.remap can pick proper version of a kfunc for the calling
context. Use this logic to select bpf_dynptr_from_skb or
bpf_dynptr_from_skb_rdonly. This will make the verifier simpler.

Unfortunately, btf_kfunc_id_set.remap cannot cover the DYNPTR_TYPE_SKB
logic in check_kfunc_args(). This can be addressed later.

Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/bpf/verifier.c | 25 ++++++----------------
 net/core/filter.c     | 49 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 51 insertions(+), 23 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2188b6674266..55e710e318e5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11750,6 +11750,7 @@ enum special_kfunc_type {
 	KF_bpf_rbtree_add_impl,
 	KF_bpf_rbtree_first,
 	KF_bpf_dynptr_from_skb,
+	KF_bpf_dynptr_from_skb_rdonly,
 	KF_bpf_dynptr_from_xdp,
 	KF_bpf_dynptr_slice,
 	KF_bpf_dynptr_slice_rdwr,
@@ -11785,6 +11786,7 @@ BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
 #ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
 BTF_ID(func, bpf_dynptr_from_xdp)
 #endif
 BTF_ID(func, bpf_dynptr_slice)
@@ -11816,10 +11818,12 @@ BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
 #ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
 BTF_ID(func, bpf_dynptr_from_xdp)
 #else
 BTF_ID_UNUSED
 BTF_ID_UNUSED
+BTF_ID_UNUSED
 #endif
 BTF_ID(func, bpf_dynptr_slice)
 BTF_ID(func, bpf_dynptr_slice_rdwr)
@@ -12741,7 +12745,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 			if (is_kfunc_arg_uninit(btf, &args[i]))
 				dynptr_arg_type |= MEM_UNINIT;
 
-			if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
+			if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb] ||
+			    meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb_rdonly]) {
 				dynptr_arg_type |= DYNPTR_TYPE_SKB;
 			} else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_xdp]) {
 				dynptr_arg_type |= DYNPTR_TYPE_XDP;
@@ -20898,9 +20903,7 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
 			     u32 func_id, u16 offset, unsigned long *addr)
 {
 	struct bpf_prog *prog = env->prog;
-	bool seen_direct_write;
 	void *xdp_kfunc;
-	bool is_rdonly;
 
 	if (bpf_dev_bound_kfunc_id(func_id)) {
 		xdp_kfunc = bpf_dev_bound_resolve_kfunc(prog, func_id);
@@ -20910,22 +20913,6 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
 		}
 		/* fallback to default kfunc when not supported by netdev */
 	}
-
-	if (offset)
-		return;
-
-	if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
-		seen_direct_write = env->seen_direct_write;
-		is_rdonly = !may_access_direct_pkt_data(env, NULL, BPF_WRITE);
-
-		if (is_rdonly)
-			*addr = (unsigned long)bpf_dynptr_from_skb_rdonly;
-
-		/* restore env->seen_direct_write to its original value, since
-		 * may_access_direct_pkt_data mutates it
-		 */
-		env->seen_direct_write = seen_direct_write;
-	}
 }
 
 static void __fixup_collection_insert_kfunc(struct bpf_insn_aux_data *insn_aux,
diff --git a/net/core/filter.c b/net/core/filter.c
index 2ec162dd83c4..6416689e3976 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12062,10 +12062,8 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
 #endif
 }
 
-__bpf_kfunc_end_defs();
-
-int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
-			       struct bpf_dynptr *ptr__uninit)
+__bpf_kfunc int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
+					   struct bpf_dynptr *ptr__uninit)
 {
 	struct bpf_dynptr_kern *ptr = (struct bpf_dynptr_kern *)ptr__uninit;
 	int err;
@@ -12079,10 +12077,16 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
 	return 0;
 }
 
+__bpf_kfunc_end_defs();
+
 BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
 BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_skb)
 
+BTF_HIDDEN_KFUNCS_START(bpf_kfunc_check_hidden_set_skb)
+BTF_ID_FLAGS(func, bpf_dynptr_from_skb_rdonly, KF_TRUSTED_ARGS)
+BTF_KFUNCS_END(bpf_kfunc_check_hidden_set_skb)
+
 BTF_KFUNCS_START(bpf_kfunc_check_set_xdp)
 BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
 BTF_KFUNCS_END(bpf_kfunc_check_set_xdp)
@@ -12095,9 +12099,46 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_tcp_reqsk)
 BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_tcp_reqsk)
 
+BTF_ID_LIST(bpf_dynptr_from_skb_list)
+BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
+
+static u32 bpf_kfunc_set_skb_remap(const struct bpf_prog *prog, u32 kfunc_id)
+{
+	if (kfunc_id != bpf_dynptr_from_skb_list[0])
+		return 0;
+
+	switch (resolve_prog_type(prog)) {
+	/* Program types only with direct read access go here! */
+	case BPF_PROG_TYPE_LWT_IN:
+	case BPF_PROG_TYPE_LWT_OUT:
+	case BPF_PROG_TYPE_LWT_SEG6LOCAL:
+	case BPF_PROG_TYPE_SK_REUSEPORT:
+	case BPF_PROG_TYPE_FLOW_DISSECTOR:
+	case BPF_PROG_TYPE_CGROUP_SKB:
+		return bpf_dynptr_from_skb_list[1];
+
+	/* Program types with direct read + write access go here! */
+	case BPF_PROG_TYPE_SCHED_CLS:
+	case BPF_PROG_TYPE_SCHED_ACT:
+	case BPF_PROG_TYPE_XDP:
+	case BPF_PROG_TYPE_LWT_XMIT:
+	case BPF_PROG_TYPE_SK_SKB:
+	case BPF_PROG_TYPE_SK_MSG:
+	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
+		return kfunc_id;
+
+	default:
+		break;
+	}
+	return bpf_dynptr_from_skb_list[1];
+}
+
 static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
 	.owner = THIS_MODULE,
 	.set = &bpf_kfunc_check_set_skb,
+	.hidden_set = &bpf_kfunc_check_hidden_set_skb,
+	.remap = &bpf_kfunc_set_skb_remap,
 };
 
 static const struct btf_kfunc_id_set bpf_kfunc_set_xdp = {
-- 
2.43.5

[PATCH v11 bpf-next 6/7] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs

[Song Liu]

Add the following kfuncs to set and remove xattrs from BPF programs:

  bpf_set_dentry_xattr
  bpf_remove_dentry_xattr
  bpf_set_dentry_xattr_locked
  bpf_remove_dentry_xattr_locked

The _locked version of these kfuncs are called from hooks where
dentry->d_inode is already locked. Instead of requiring the user
to know which version of the kfuncs to use, the verifier will pick
the proper kfunc based on the calling hook.

Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
---
 fs/bpf_fs_kfuncs.c      | 219 +++++++++++++++++++++++++++++++++++++++-
 include/linux/bpf_lsm.h |   2 +
 2 files changed, 219 insertions(+), 2 deletions(-)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 8a65184c8c2c..28a0ec5516af 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -2,10 +2,12 @@
 /* Copyright (c) 2024 Google LLC. */
 
 #include <linux/bpf.h>
+#include <linux/bpf_lsm.h>
 #include <linux/btf.h>
 #include <linux/btf_ids.h>
 #include <linux/dcache.h>
 #include <linux/fs.h>
+#include <linux/fsnotify.h>
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/xattr.h>
@@ -161,6 +163,156 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
 	return bpf_get_dentry_xattr(dentry, name__str, value_p);
 }
 
+static int bpf_xattr_write_permission(const char *name, struct inode *inode)
+{
+	if (WARN_ON(!inode))
+		return -EINVAL;
+
+	/* Only allow setting and removing security.bpf. xattrs */
+	if (!match_security_bpf_prefix(name))
+		return -EPERM;
+
+	return inode_permission(&nop_mnt_idmap, inode, MAY_WRITE);
+}
+
+/**
+ * bpf_set_dentry_xattr_locked - set a xattr of a dentry
+ * @dentry: dentry to get xattr from
+ * @name__str: name of the xattr
+ * @value_p: xattr value
+ * @flags: flags to pass into filesystem operations
+ *
+ * Set xattr *name__str* of *dentry* to the value in *value_ptr*.
+ *
+ * For security reasons, only *name__str* with prefix "security.bpf."
+ * is allowed.
+ *
+ * The caller already locked dentry->d_inode.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_set_dentry_xattr_locked(struct dentry *dentry, const char *name__str,
+					    const struct bpf_dynptr *value_p, int flags)
+{
+
+	struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
+	struct inode *inode = d_inode(dentry);
+	const void *value;
+	u32 value_len;
+	int ret;
+
+	value_len = __bpf_dynptr_size(value_ptr);
+	value = __bpf_dynptr_data(value_ptr, value_len);
+	if (!value)
+		return -EINVAL;
+
+	ret = bpf_xattr_write_permission(name__str, inode);
+	if (ret)
+		return ret;
+
+	ret = __vfs_setxattr(&nop_mnt_idmap, dentry, inode, name__str,
+			     value, value_len, flags);
+	if (!ret) {
+		fsnotify_xattr(dentry);
+
+		/* This xattr is set by BPF LSM, so we do not call
+		 * security_inode_post_setxattr. Otherwise, we would
+		 * risk deadlocks by calling back to the same kfunc.
+		 *
+		 * This is the same as security_inode_setsecurity().
+		 */
+	}
+	return ret;
+}
+
+/**
+ * bpf_set_dentry_xattr - set a xattr of a dentry
+ * @dentry: dentry to get xattr from
+ * @name__str: name of the xattr
+ * @value_p: xattr value
+ * @flags: flags to pass into filesystem operations
+ *
+ * Set xattr *name__str* of *dentry* to the value in *value_ptr*.
+ *
+ * For security reasons, only *name__str* with prefix "security.bpf."
+ * is allowed.
+ *
+ * The caller has not locked dentry->d_inode.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_set_dentry_xattr(struct dentry *dentry, const char *name__str,
+				     const struct bpf_dynptr *value_p, int flags)
+{
+	struct inode *inode = d_inode(dentry);
+	int ret;
+
+	inode_lock(inode);
+	ret = bpf_set_dentry_xattr_locked(dentry, name__str, value_p, flags);
+	inode_unlock(inode);
+	return ret;
+}
+
+/**
+ * bpf_remove_dentry_xattr_locked - remove a xattr of a dentry
+ * @dentry: dentry to get xattr from
+ * @name__str: name of the xattr
+ *
+ * Rmove xattr *name__str* of *dentry*.
+ *
+ * For security reasons, only *name__str* with prefix "security.bpf."
+ * is allowed.
+ *
+ * The caller already locked dentry->d_inode.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_remove_dentry_xattr_locked(struct dentry *dentry, const char *name__str)
+{
+	struct inode *inode = d_inode(dentry);
+	int ret;
+
+	ret = bpf_xattr_write_permission(name__str, inode);
+	if (ret)
+		return ret;
+
+	ret = __vfs_removexattr(&nop_mnt_idmap, dentry, name__str);
+	if (!ret) {
+		fsnotify_xattr(dentry);
+
+		/* This xattr is removed by BPF LSM, so we do not call
+		 * security_inode_post_removexattr. Otherwise, we would
+		 * risk deadlocks by calling back to the same kfunc.
+		 */
+	}
+	return ret;
+}
+
+/**
+ * bpf_remove_dentry_xattr - remove a xattr of a dentry
+ * @dentry: dentry to get xattr from
+ * @name__str: name of the xattr
+ *
+ * Rmove xattr *name__str* of *dentry*.
+ *
+ * For security reasons, only *name__str* with prefix "security.bpf."
+ * is allowed.
+ *
+ * The caller has not locked dentry->d_inode.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name__str)
+{
+	struct inode *inode = d_inode(dentry);
+	int ret;
+
+	inode_lock(inode);
+	ret = bpf_remove_dentry_xattr_locked(dentry, name__str);
+	inode_unlock(inode);
+	return ret;
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)
@@ -170,20 +322,83 @@ BTF_ID_FLAGS(func, bpf_put_file, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_path_d_path, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_get_dentry_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE | KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)
 
+BTF_HIDDEN_KFUNCS_START(bpf_fs_kfunc_hidden_set_ids)
+BTF_ID_FLAGS(func, bpf_set_dentry_xattr_locked, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_remove_dentry_xattr_locked, KF_SLEEPABLE | KF_TRUSTED_ARGS)
+BTF_KFUNCS_END(bpf_fs_kfunc_hidden_set_ids)
+
 static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
 {
-	if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) ||
-	    prog->type == BPF_PROG_TYPE_LSM)
+	if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) &&
+	    !btf_id_set8_contains(&bpf_fs_kfunc_hidden_set_ids, kfunc_id))
+		return 0;
+	if (prog->type == BPF_PROG_TYPE_LSM)
 		return 0;
 	return -EACCES;
 }
 
+/* bpf_[set|remove]_dentry_xattr.* hooks have KF_TRUSTED_ARGS and
+ * KF_SLEEPABLE, so they are only available to sleepable hooks with
+ * dentry arguments.
+ *
+ * Setting and removing xattr requires exclusive lock on dentry->d_inode.
+ * Some hooks already locked d_inode, while some hooks have not locked
+ * d_inode. Therefore, we need different kfuncs for different hooks.
+ * Specifically, hooks in the following list (d_inode_locked_hooks)
+ * should call bpf_[set|remove]_dentry_xattr_locked; while other hooks
+ * should call bpf_[set|remove]_dentry_xattr.
+ */
+BTF_SET_START(d_inode_locked_hooks)
+BTF_ID(func, bpf_lsm_inode_post_removexattr)
+BTF_ID(func, bpf_lsm_inode_post_setattr)
+BTF_ID(func, bpf_lsm_inode_post_setxattr)
+BTF_ID(func, bpf_lsm_inode_removexattr)
+BTF_ID(func, bpf_lsm_inode_rmdir)
+BTF_ID(func, bpf_lsm_inode_setattr)
+BTF_ID(func, bpf_lsm_inode_setxattr)
+BTF_ID(func, bpf_lsm_inode_unlink)
+#ifdef CONFIG_SECURITY_PATH
+BTF_ID(func, bpf_lsm_path_unlink)
+BTF_ID(func, bpf_lsm_path_rmdir)
+#endif /* CONFIG_SECURITY_PATH */
+BTF_SET_END(d_inode_locked_hooks)
+
+static bool bpf_lsm_has_d_inode_locked(const struct bpf_prog *prog)
+{
+	return btf_id_set_contains(&d_inode_locked_hooks, prog->aux->attach_btf_id);
+}
+
+BTF_ID_LIST(not_locked_fs_kfuncs)
+BTF_ID(func, bpf_set_dentry_xattr)
+BTF_ID(func, bpf_remove_dentry_xattr)
+
+BTF_ID_LIST(locked_fs_kfuncs)
+BTF_ID(func, bpf_set_dentry_xattr_locked)
+BTF_ID(func, bpf_remove_dentry_xattr_locked)
+
+static u32 bpf_fs_kfunc_remap(const struct bpf_prog *prog, u32 kfunc_id)
+{
+	if (!bpf_lsm_has_d_inode_locked(prog))
+		return 0;
+
+	if (kfunc_id == not_locked_fs_kfuncs[0])
+		return locked_fs_kfuncs[0];
+	if (kfunc_id == not_locked_fs_kfuncs[1])
+		return locked_fs_kfuncs[1];
+
+	return 0;
+}
+
 static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
 	.owner = THIS_MODULE,
 	.set = &bpf_fs_kfunc_set_ids,
+	.hidden_set = &bpf_fs_kfunc_hidden_set_ids,
 	.filter = bpf_fs_kfuncs_filter,
+	.remap = bpf_fs_kfunc_remap,
 };
 
 static int __init bpf_fs_kfuncs_init(void)
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index aefcd6564251..f4ab0dc1df69 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -48,6 +48,7 @@ void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func)
 
 int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
 			     struct bpf_retval_range *range);
+
 #else /* !CONFIG_BPF_LSM */
 
 static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
@@ -86,6 +87,7 @@ static inline int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
 {
 	return -EOPNOTSUPP;
 }
+
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */
-- 
2.43.5

[PATCH v11 bpf-next 7/7] selftests/bpf: Test kfuncs that set and remove xattr from BPF programs

[Song Liu]

Two sets of tests are added to exercise the not _locked and _locked
version of the kfuncs. For both tests, user space accesses xattr
security.bpf.foo on a testfile. The BPF program is triggered by user
space access (on LSM hook inode_[set|get]_xattr) and sets or removes
xattr security.bpf.bar. Then user space then validates that xattr
security.bpf.bar is set or removed as expected.

Note that, in both tests, the BPF programs use the not _locked kfuncs.
The verifier picks the proper kfuncs based on the calling context.

Signed-off-by: Song Liu <song@kernel.org>
---
 tools/testing/selftests/bpf/bpf_kfuncs.h      |   5 +
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 125 ++++++++++++++++
 .../bpf/progs/test_set_remove_xattr.c         | 133 ++++++++++++++++++
 3 files changed, 263 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_set_remove_xattr.c

diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index 2eb3483f2fb0..8215c9b3115e 100644
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -87,4 +87,9 @@ struct dentry;
  */
 extern int bpf_get_dentry_xattr(struct dentry *dentry, const char *name,
 			      struct bpf_dynptr *value_ptr) __ksym __weak;
+
+extern int bpf_set_dentry_xattr(struct dentry *dentry, const char *name__str,
+				const struct bpf_dynptr *value_p, int flags) __ksym __weak;
+extern int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name__str) __ksym __weak;
+
 #endif
diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 419f45b56472..43a26ec69a8e 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include <test_progs.h>
 #include "test_get_xattr.skel.h"
+#include "test_set_remove_xattr.skel.h"
 #include "test_fsverity.skel.h"
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
@@ -72,6 +73,127 @@ static void test_get_xattr(const char *name, const char *value, bool allow_acces
 	remove(testfile);
 }
 
+/* xattr value we will set to security.bpf.foo */
+static const char value_foo[] = "hello";
+
+static void read_and_validate_foo(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_foo, value_out, sizeof(value_out));
+	ASSERT_EQ(err, sizeof(value_foo), "getxattr size foo");
+	ASSERT_EQ(strncmp(value_out, value_foo, sizeof(value_foo)), 0, "strncmp value_foo");
+}
+
+static void set_foo(struct test_set_remove_xattr *skel)
+{
+	ASSERT_OK(setxattr(testfile, skel->rodata->xattr_foo, value_foo, strlen(value_foo) + 1, 0),
+		  "setxattr foo");
+}
+
+static void validate_bar_match(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_bar, value_out, sizeof(value_out));
+	ASSERT_EQ(err, sizeof(skel->data->value_bar), "getxattr size bar");
+	ASSERT_EQ(strncmp(value_out, skel->data->value_bar, sizeof(skel->data->value_bar)), 0,
+		  "strncmp value_bar");
+}
+
+static void validate_bar_removed(struct test_set_remove_xattr *skel)
+{
+	char value_out[32];
+	int err;
+
+	err = getxattr(testfile, skel->rodata->xattr_bar, value_out, sizeof(value_out));
+	ASSERT_LT(err, 0, "getxattr size bar should fail");
+}
+
+static void test_set_remove_xattr(void)
+{
+	struct test_set_remove_xattr *skel = NULL;
+	int fd = -1, err;
+
+	fd = open(testfile, O_CREAT | O_RDONLY, 0644);
+	if (!ASSERT_GE(fd, 0, "create_file"))
+		return;
+
+	close(fd);
+	fd = -1;
+
+	skel = test_set_remove_xattr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_set_remove_xattr__open_and_load"))
+		return;
+
+	/* Set security.bpf.foo to "hello" */
+	err = setxattr(testfile, skel->rodata->xattr_foo, value_foo, strlen(value_foo) + 1, 0);
+	if (err && errno == EOPNOTSUPP) {
+		printf("%s:SKIP:local fs doesn't support xattr (%d)\n"
+		       "To run this test, make sure /tmp filesystem supports xattr.\n",
+		       __func__, errno);
+		test__skip();
+		goto out;
+	}
+
+	if (!ASSERT_OK(err, "setxattr"))
+		goto out;
+
+	skel->bss->monitored_pid = getpid();
+	err = test_set_remove_xattr__attach(skel);
+	if (!ASSERT_OK(err, "test_set_remove_xattr__attach"))
+		goto out;
+
+	/* First, test not _locked version of the kfuncs with getxattr. */
+
+	/* Read security.bpf.foo and trigger test_inode_getxattr. This
+	 * bpf program will set security.bpf.bar to "world".
+	 */
+	read_and_validate_foo(skel);
+	validate_bar_match(skel);
+
+	/* Read security.bpf.foo and trigger test_inode_getxattr again.
+	 * This will remove xattr security.bpf.bar.
+	 */
+	read_and_validate_foo(skel);
+	validate_bar_removed(skel);
+
+	ASSERT_TRUE(skel->bss->set_security_bpf_bar_success, "set_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->remove_security_bpf_bar_success, "remove_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->set_security_selinux_fail, "set_security_selinux_fail");
+	ASSERT_TRUE(skel->bss->remove_security_selinux_fail, "remove_security_selinux_fail");
+
+	/* Second, test _locked version of the kfuncs, with setxattr */
+
+	/* Set security.bpf.foo and trigger test_inode_setxattr. This
+	 * bpf program will set security.bpf.bar to "world".
+	 */
+	set_foo(skel);
+	validate_bar_match(skel);
+
+	/* Set security.bpf.foo and trigger test_inode_setxattr again.
+	 * This will remove xattr security.bpf.bar.
+	 */
+	set_foo(skel);
+	validate_bar_removed(skel);
+
+	ASSERT_TRUE(skel->bss->locked_set_security_bpf_bar_success,
+		    "locked_set_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->locked_remove_security_bpf_bar_success,
+		    "locked_remove_security_bpf_bar_success");
+	ASSERT_TRUE(skel->bss->locked_set_security_selinux_fail,
+		    "locked_set_security_selinux_fail");
+	ASSERT_TRUE(skel->bss->locked_remove_security_selinux_fail,
+		    "locked_remove_security_selinux_fail");
+
+out:
+	close(fd);
+	test_set_remove_xattr__destroy(skel);
+	remove(testfile);
+}
+
 #ifndef SHA256_DIGEST_SIZE
 #define SHA256_DIGEST_SIZE      32
 #endif
@@ -161,6 +283,9 @@ void test_fs_kfuncs(void)
 	if (test__start_subtest("security_selinux_xattr_error"))
 		test_get_xattr("security.selinux", "hello", false);
 
+	if (test__start_subtest("set_remove_xattr"))
+		test_set_remove_xattr();
+
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
 }
diff --git a/tools/testing/selftests/bpf/progs/test_set_remove_xattr.c b/tools/testing/selftests/bpf/progs/test_set_remove_xattr.c
new file mode 100644
index 000000000000..6a612cf168d3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_set_remove_xattr.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_kfuncs.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+__u32 monitored_pid;
+
+const char xattr_foo[] = "security.bpf.foo";
+const char xattr_bar[] = "security.bpf.bar";
+static const char xattr_selinux[] = "security.selinux";
+char value_bar[] = "world";
+char read_value[32];
+
+bool set_security_bpf_bar_success;
+bool remove_security_bpf_bar_success;
+bool set_security_selinux_fail;
+bool remove_security_selinux_fail;
+
+char name_buf[32];
+
+static inline bool name_match_foo(const char *name)
+{
+	bpf_probe_read_kernel(name_buf, sizeof(name_buf), name);
+
+	return !bpf_strncmp(name_buf, sizeof(xattr_foo), xattr_foo);
+}
+
+/* Test bpf_set_dentry_xattr and bpf_remove_dentry_xattr */
+SEC("lsm.s/inode_getxattr")
+int BPF_PROG(test_inode_getxattr, struct dentry *dentry, char *name)
+{
+	struct bpf_dynptr value_ptr;
+	__u32 pid;
+	int ret;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	/* Only do the following for security.bpf.foo */
+	if (!name_match_foo(name))
+		return 0;
+
+	bpf_dynptr_from_mem(read_value, sizeof(read_value), 0, &value_ptr);
+
+	/* read security.bpf.bar */
+	ret = bpf_get_dentry_xattr(dentry, xattr_bar, &value_ptr);
+
+	if (ret < 0) {
+		/* If security.bpf.bar doesn't exist, set it */
+		bpf_dynptr_from_mem(value_bar, sizeof(value_bar), 0, &value_ptr);
+
+		ret = bpf_set_dentry_xattr(dentry, xattr_bar, &value_ptr, 0);
+		if (!ret)
+			set_security_bpf_bar_success = true;
+		ret = bpf_set_dentry_xattr(dentry, xattr_selinux, &value_ptr, 0);
+		if (ret)
+			set_security_selinux_fail = true;
+	} else {
+		/* If security.bpf.bar exists, remove it */
+		ret = bpf_remove_dentry_xattr(dentry, xattr_bar);
+		if (!ret)
+			remove_security_bpf_bar_success = true;
+
+		ret = bpf_remove_dentry_xattr(dentry, xattr_selinux);
+		if (ret)
+			remove_security_selinux_fail = true;
+	}
+
+	return 0;
+}
+
+bool locked_set_security_bpf_bar_success;
+bool locked_remove_security_bpf_bar_success;
+bool locked_set_security_selinux_fail;
+bool locked_remove_security_selinux_fail;
+
+/* Test bpf_set_dentry_xattr_locked and bpf_remove_dentry_xattr_locked.
+ * It not necessary to differentiate the _locked version and the
+ * not-_locked version in the BPF program. The verifier will fix them up
+ * properly.
+ */
+SEC("lsm.s/inode_setxattr")
+int BPF_PROG(test_inode_setxattr, struct mnt_idmap *idmap,
+	     struct dentry *dentry, const char *name,
+	     const void *value, size_t size, int flags)
+{
+	struct bpf_dynptr value_ptr;
+	__u32 pid;
+	int ret;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	/* Only do the following for security.bpf.foo */
+	if (!name_match_foo(name))
+		return 0;
+
+	bpf_dynptr_from_mem(read_value, sizeof(read_value), 0, &value_ptr);
+
+	/* read security.bpf.bar */
+	ret = bpf_get_dentry_xattr(dentry, xattr_bar, &value_ptr);
+
+	if (ret < 0) {
+		/* If security.bpf.bar doesn't exist, set it */
+		bpf_dynptr_from_mem(value_bar, sizeof(value_bar), 0, &value_ptr);
+
+		ret = bpf_set_dentry_xattr(dentry, xattr_bar, &value_ptr, 0);
+		if (!ret)
+			locked_set_security_bpf_bar_success = true;
+		ret = bpf_set_dentry_xattr(dentry, xattr_selinux, &value_ptr, 0);
+		if (ret)
+			locked_set_security_selinux_fail = true;
+	} else {
+		/* If security.bpf.bar exists, remove it */
+		ret = bpf_remove_dentry_xattr(dentry, xattr_bar);
+		if (!ret)
+			locked_remove_security_bpf_bar_success = true;
+
+		ret = bpf_remove_dentry_xattr(dentry, xattr_selinux);
+		if (ret)
+			locked_remove_security_selinux_fail = true;
+	}
+
+	return 0;
+}
-- 
2.43.5

Re: [PATCH v11 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Alexei Starovoitov]

On Wed, Jan 29, 2025 at 1:00 PM Song Liu <song@kernel.org> wrote:
>
> btf_kfunc_id_set.remap can pick proper version of a kfunc for the calling
> context. Use this logic to select bpf_dynptr_from_skb or
> bpf_dynptr_from_skb_rdonly. This will make the verifier simpler.
>
> Unfortunately, btf_kfunc_id_set.remap cannot cover the DYNPTR_TYPE_SKB
> logic in check_kfunc_args(). This can be addressed later.
>
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  kernel/bpf/verifier.c | 25 ++++++----------------
>  net/core/filter.c     | 49 +++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 51 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2188b6674266..55e710e318e5 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -11750,6 +11750,7 @@ enum special_kfunc_type {
>         KF_bpf_rbtree_add_impl,
>         KF_bpf_rbtree_first,
>         KF_bpf_dynptr_from_skb,
> +       KF_bpf_dynptr_from_skb_rdonly,
>         KF_bpf_dynptr_from_xdp,
>         KF_bpf_dynptr_slice,
>         KF_bpf_dynptr_slice_rdwr,
> @@ -11785,6 +11786,7 @@ BTF_ID(func, bpf_rbtree_add_impl)
>  BTF_ID(func, bpf_rbtree_first)
>  #ifdef CONFIG_NET
>  BTF_ID(func, bpf_dynptr_from_skb)
> +BTF_ID(func, bpf_dynptr_from_skb_rdonly)
>  BTF_ID(func, bpf_dynptr_from_xdp)
>  #endif
>  BTF_ID(func, bpf_dynptr_slice)
> @@ -11816,10 +11818,12 @@ BTF_ID(func, bpf_rbtree_add_impl)
>  BTF_ID(func, bpf_rbtree_first)
>  #ifdef CONFIG_NET
>  BTF_ID(func, bpf_dynptr_from_skb)
> +BTF_ID(func, bpf_dynptr_from_skb_rdonly)
>  BTF_ID(func, bpf_dynptr_from_xdp)
>  #else
>  BTF_ID_UNUSED
>  BTF_ID_UNUSED
> +BTF_ID_UNUSED
>  #endif
>  BTF_ID(func, bpf_dynptr_slice)
>  BTF_ID(func, bpf_dynptr_slice_rdwr)
> @@ -12741,7 +12745,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
>                         if (is_kfunc_arg_uninit(btf, &args[i]))
>                                 dynptr_arg_type |= MEM_UNINIT;
>
> -                       if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
> +                       if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb] ||
> +                           meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb_rdonly]) {
>                                 dynptr_arg_type |= DYNPTR_TYPE_SKB;
>                         } else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_xdp]) {
>                                 dynptr_arg_type |= DYNPTR_TYPE_XDP;
> @@ -20898,9 +20903,7 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
>                              u32 func_id, u16 offset, unsigned long *addr)
>  {
>         struct bpf_prog *prog = env->prog;
> -       bool seen_direct_write;
>         void *xdp_kfunc;
> -       bool is_rdonly;
>
>         if (bpf_dev_bound_kfunc_id(func_id)) {
>                 xdp_kfunc = bpf_dev_bound_resolve_kfunc(prog, func_id);
> @@ -20910,22 +20913,6 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
>                 }
>                 /* fallback to default kfunc when not supported by netdev */
>         }
> -
> -       if (offset)
> -               return;
> -
> -       if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
> -               seen_direct_write = env->seen_direct_write;
> -               is_rdonly = !may_access_direct_pkt_data(env, NULL, BPF_WRITE);
> -
> -               if (is_rdonly)
> -                       *addr = (unsigned long)bpf_dynptr_from_skb_rdonly;
> -
> -               /* restore env->seen_direct_write to its original value, since
> -                * may_access_direct_pkt_data mutates it
> -                */
> -               env->seen_direct_write = seen_direct_write;
> -       }
>  }
>
>  static void __fixup_collection_insert_kfunc(struct bpf_insn_aux_data *insn_aux,
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2ec162dd83c4..6416689e3976 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -12062,10 +12062,8 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
>  #endif
>  }
>
> -__bpf_kfunc_end_defs();
> -
> -int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
> -                              struct bpf_dynptr *ptr__uninit)
> +__bpf_kfunc int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
> +                                          struct bpf_dynptr *ptr__uninit)
>  {
>         struct bpf_dynptr_kern *ptr = (struct bpf_dynptr_kern *)ptr__uninit;
>         int err;
> @@ -12079,10 +12077,16 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
>         return 0;
>  }
>
> +__bpf_kfunc_end_defs();
> +
>  BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
>  BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
>  BTF_KFUNCS_END(bpf_kfunc_check_set_skb)
>
> +BTF_HIDDEN_KFUNCS_START(bpf_kfunc_check_hidden_set_skb)
> +BTF_ID_FLAGS(func, bpf_dynptr_from_skb_rdonly, KF_TRUSTED_ARGS)
> +BTF_KFUNCS_END(bpf_kfunc_check_hidden_set_skb)
> +
>  BTF_KFUNCS_START(bpf_kfunc_check_set_xdp)
>  BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
>  BTF_KFUNCS_END(bpf_kfunc_check_set_xdp)
> @@ -12095,9 +12099,46 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_tcp_reqsk)
>  BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS)
>  BTF_KFUNCS_END(bpf_kfunc_check_set_tcp_reqsk)
>
> +BTF_ID_LIST(bpf_dynptr_from_skb_list)
> +BTF_ID(func, bpf_dynptr_from_skb)
> +BTF_ID(func, bpf_dynptr_from_skb_rdonly)
> +
> +static u32 bpf_kfunc_set_skb_remap(const struct bpf_prog *prog, u32 kfunc_id)
> +{
> +       if (kfunc_id != bpf_dynptr_from_skb_list[0])
> +               return 0;
> +
> +       switch (resolve_prog_type(prog)) {
> +       /* Program types only with direct read access go here! */
> +       case BPF_PROG_TYPE_LWT_IN:
> +       case BPF_PROG_TYPE_LWT_OUT:
> +       case BPF_PROG_TYPE_LWT_SEG6LOCAL:
> +       case BPF_PROG_TYPE_SK_REUSEPORT:
> +       case BPF_PROG_TYPE_FLOW_DISSECTOR:
> +       case BPF_PROG_TYPE_CGROUP_SKB:

This copy pastes the logic from may_access_direct_pkt_data(),
so any future change to that helper would need to update
this one as well.

> +               return bpf_dynptr_from_skb_list[1];

The [0] and [1] stuff is quite error prone.

> +
> +       /* Program types with direct read + write access go here! */
> +       case BPF_PROG_TYPE_SCHED_CLS:
> +       case BPF_PROG_TYPE_SCHED_ACT:
> +       case BPF_PROG_TYPE_XDP:
> +       case BPF_PROG_TYPE_LWT_XMIT:
> +       case BPF_PROG_TYPE_SK_SKB:
> +       case BPF_PROG_TYPE_SK_MSG:
> +       case BPF_PROG_TYPE_CGROUP_SOCKOPT:
> +               return kfunc_id;
> +
> +       default:
> +               break;
> +       }
> +       return bpf_dynptr_from_skb_list[1];
> +}
> +
>  static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
>         .owner = THIS_MODULE,
>         .set = &bpf_kfunc_check_set_skb,
> +       .hidden_set = &bpf_kfunc_check_hidden_set_skb,

If I'm reading it correctly the hidden_set serves no additional purpose.
It splits the set into two, but patch 4 just adds them together.

> +       .remap = &bpf_kfunc_set_skb_remap,

I'm not a fan of callbacks in general.
The makes everything harder to follow.

For all these reasons I don't like this approach.
This "generality" doesn't make it cleaner or easier to extend.
For the patch 6... just repeat what specialize_kfunc()
currently does for dynptr ?


pw-bot: cr

Re: [PATCH v11 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

[Matt Bobrowski]

On Wed, Jan 29, 2025 at 12:59:51PM -0800, Song Liu wrote:
> Introduct new xattr name prefix security.bpf., and enable reading these
> xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr().
> 
> As we are on it, correct the comments for return value of
> bpf_get_[file|dentry]_xattr(), i.e. return length the xattr value on
> success.

Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>

> Signed-off-by: Song Liu <song@kernel.org>
> Acked-by: Christian Brauner <brauner@kernel.org>
> Reviewed-by: Jan Kara <jack@suse.cz>
> ---
>  fs/bpf_fs_kfuncs.c         | 19 ++++++++++++++-----
>  include/uapi/linux/xattr.h |  4 ++++
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 3fe9f59ef867..8a65184c8c2c 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -93,6 +93,11 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
>  	return len;
>  }
>  
> +static bool match_security_bpf_prefix(const char *name__str)
> +{
> +	return !strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN);
> +}

I think this can also just be match_xattr_prefix(const char
*name__str, const char *prefix, size_t len) such that we can do the
same checks for aribitrary xattr prefixes i.e. XATTR_USER_PREFIX,
XATTR_NAME_BPF_LSM.

>  /**
>   * bpf_get_dentry_xattr - get xattr of a dentry
>   * @dentry: dentry to get xattr from
> @@ -101,9 +106,10 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
>   *
>   * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
>   *
> - * For security reasons, only *name__str* with prefix "user." is allowed.
> + * For security reasons, only *name__str* with prefix "user." or
      	  	   	    	 	     	  ^ prefixes
						  
> + * "security.bpf." is allowed.
                      ^ are

Out of curiosity, what is the security reasoning here? This isn't
obvious to me, and I'd like to understand this better. Is it simply
frowned upon to read arbitrary xattr values from the context of a BPF
LSM program, or has it got something to do with the backing xattr
handler that ends up being called once we step into __vfs_getxattr()
and such?  Also, just so that it's clear, I don't have anything
against this allow listing approach either, I just genuinely don't
understand the security implications.

> - * Return: 0 on success, a negative value on error.
> + * Return: length of the xattr value on success, a negative value on error.
>   */
>  __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
>  				     struct bpf_dynptr *value_p)
> @@ -117,7 +123,9 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
>  	if (WARN_ON(!inode))
>  		return -EINVAL;
>  
> -	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
> +	/* Allow reading xattr with user. and security.bpf. prefix */
> +	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
> +	    !match_security_bpf_prefix(name__str))

I think it would be cleaner to have single function
i.e. is_allowed_xattr_prefix(const char *name__str) which simply
checks all the allowed xattr prefixes that can be read by this BPF
kfunc.

>  		return -EPERM;
>  
>  	value_len = __bpf_dynptr_size(value_ptr);
> @@ -139,9 +147,10 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
>   *
>   * Get xattr *name__str* of *file* and store the output in *value_ptr*.
>   *
> - * For security reasons, only *name__str* with prefix "user." is allowed.
> + * For security reasons, only *name__str* with prefix "user." or
      	  	   	    	 	     	  ^ prefixes

> + * "security.bpf." is allowed.
      		      ^ are

> - * Return: 0 on success, a negative value on error.
> + * Return: length of the xattr value on success, a negative value on error.
>   */
>  __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
>  				   struct bpf_dynptr *value_p)
> diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
> index 9854f9cff3c6..c7c85bb504ba 100644
> --- a/include/uapi/linux/xattr.h
> +++ b/include/uapi/linux/xattr.h
> @@ -83,6 +83,10 @@ struct xattr_args {
>  #define XATTR_CAPS_SUFFIX "capability"
>  #define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX
>  
> +#define XATTR_BPF_LSM_SUFFIX "bpf."
> +#define XATTR_NAME_BPF_LSM (XATTR_SECURITY_PREFIX XATTR_BPF_LSM_SUFFIX)
> +#define XATTR_NAME_BPF_LSM_LEN (sizeof(XATTR_NAME_BPF_LSM) - 1)
> +
>  #define XATTR_POSIX_ACL_ACCESS  "posix_acl_access"
>  #define XATTR_NAME_POSIX_ACL_ACCESS XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_ACCESS
>  #define XATTR_POSIX_ACL_DEFAULT  "posix_acl_default"
> -- 
> 2.43.5
> 

Re: [PATCH v11 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

[Christian Brauner]

On Thu, Jan 30, 2025 at 10:57:35AM +0000, Matt Bobrowski wrote:
> On Wed, Jan 29, 2025 at 12:59:51PM -0800, Song Liu wrote:
> > Introduct new xattr name prefix security.bpf., and enable reading these
> > xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr().
> > 
> > As we are on it, correct the comments for return value of
> > bpf_get_[file|dentry]_xattr(), i.e. return length the xattr value on
> > success.
> 
> Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>
> 
> > Signed-off-by: Song Liu <song@kernel.org>
> > Acked-by: Christian Brauner <brauner@kernel.org>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/bpf_fs_kfuncs.c         | 19 ++++++++++++++-----
> >  include/uapi/linux/xattr.h |  4 ++++
> >  2 files changed, 18 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> > index 3fe9f59ef867..8a65184c8c2c 100644
> > --- a/fs/bpf_fs_kfuncs.c
> > +++ b/fs/bpf_fs_kfuncs.c
> > @@ -93,6 +93,11 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
> >  	return len;
> >  }
> >  
> > +static bool match_security_bpf_prefix(const char *name__str)
> > +{
> > +	return !strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN);
> > +}
> 
> I think this can also just be match_xattr_prefix(const char
> *name__str, const char *prefix, size_t len) such that we can do the
> same checks for aribitrary xattr prefixes i.e. XATTR_USER_PREFIX,
> XATTR_NAME_BPF_LSM.
> 
> >  /**
> >   * bpf_get_dentry_xattr - get xattr of a dentry
> >   * @dentry: dentry to get xattr from
> > @@ -101,9 +106,10 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
> >   *
> >   * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
> >   *
> > - * For security reasons, only *name__str* with prefix "user." is allowed.
> > + * For security reasons, only *name__str* with prefix "user." or
>       	  	   	    	 	     	  ^ prefixes
> 						  
> > + * "security.bpf." is allowed.
>                       ^ are
> 
> Out of curiosity, what is the security reasoning here? This isn't
> obvious to me, and I'd like to understand this better. Is it simply
> frowned upon to read arbitrary xattr values from the context of a BPF
> LSM program, or has it got something to do with the backing xattr
> handler that ends up being called once we step into __vfs_getxattr()
> and such?  Also, just so that it's clear, I don't have anything
> against this allow listing approach either, I just genuinely don't
> understand the security implications.

I've explained this at lenghts in multiple threads. The gist is various
xattrs require you to have access to properties that are carried by
objects you don't have access to (e.g., the mount) or can't guarantee
that you're in the correct context and interpreting those xattrs without
this information is either meaningless or actively wrong.

Re: [PATCH v11 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Song Liu]

Hi Alexei, 

Thanks for the review!

> On Jan 29, 2025, at 6:32 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

[...]

>> 
>> +BTF_ID_LIST(bpf_dynptr_from_skb_list)
>> +BTF_ID(func, bpf_dynptr_from_skb)
>> +BTF_ID(func, bpf_dynptr_from_skb_rdonly)
>> +
>> +static u32 bpf_kfunc_set_skb_remap(const struct bpf_prog *prog, u32 kfunc_id)
>> +{
>> +       if (kfunc_id != bpf_dynptr_from_skb_list[0])
>> +               return 0;
>> +
>> +       switch (resolve_prog_type(prog)) {
>> +       /* Program types only with direct read access go here! */
>> +       case BPF_PROG_TYPE_LWT_IN:
>> +       case BPF_PROG_TYPE_LWT_OUT:
>> +       case BPF_PROG_TYPE_LWT_SEG6LOCAL:
>> +       case BPF_PROG_TYPE_SK_REUSEPORT:
>> +       case BPF_PROG_TYPE_FLOW_DISSECTOR:
>> +       case BPF_PROG_TYPE_CGROUP_SKB:
> 
> This copy pastes the logic from may_access_direct_pkt_data(),
> so any future change to that helper would need to update
> this one as well.

We can probably improve this with some helpers/macros. 

> 
>> +               return bpf_dynptr_from_skb_list[1];
> 
> The [0] and [1] stuff is quite error prone.
> 
>> +
>> +       /* Program types with direct read + write access go here! */
>> +       case BPF_PROG_TYPE_SCHED_CLS:
>> +       case BPF_PROG_TYPE_SCHED_ACT:
>> +       case BPF_PROG_TYPE_XDP:
>> +       case BPF_PROG_TYPE_LWT_XMIT:
>> +       case BPF_PROG_TYPE_SK_SKB:
>> +       case BPF_PROG_TYPE_SK_MSG:
>> +       case BPF_PROG_TYPE_CGROUP_SOCKOPT:
>> +               return kfunc_id;
>> +
>> +       default:
>> +               break;
>> +       }
>> +       return bpf_dynptr_from_skb_list[1];
>> +}
>> +
>> static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
>>        .owner = THIS_MODULE,
>>        .set = &bpf_kfunc_check_set_skb,
>> +       .hidden_set = &bpf_kfunc_check_hidden_set_skb,
> 
> If I'm reading it correctly the hidden_set serves no additional purpose.
> It splits the set into two, but patch 4 just adds them together.

hidden_set does not have BTF_SET8_KFUNCS, so pahole will not export 
these kfuncs to vmlinux.h. 

> 
>> +       .remap = &bpf_kfunc_set_skb_remap,
> 
> I'm not a fan of callbacks in general.
> The makes everything harder to follow.

This motivation here is to move polymorphism logic from verifier
core to kfuncs owners. I guess we will need some callback to 
achieve this goal. Of course, we don't have to do it in this set. 
 

> For all these reasons I don't like this approach.
> This "generality" doesn't make it cleaner or easier to extend.
> For the patch 6... just repeat what specialize_kfunc()
> currently does for dynptr ?

Yes, specialize_kfunc() can handle this. But we will need to use
d_inode_locked_hooks from 6/7 in specialize_kfunc(). It works, 
but it is not clean (to me). 

I will revise this set so that the polymorphism logic in handled
in specialize_kfunc(). For longer term, maybe we should discuss 
"move some logic from verifier core to kfuncs" in the upcoming 
LSF/MM/BPF? 

Thanks,
Song

Re: [PATCH v11 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

[Song Liu]

Hi Matt,

> On Jan 30, 2025, at 2:57 AM, Matt Bobrowski <mattbobrowski@google.com> wrote:
> 
> On Wed, Jan 29, 2025 at 12:59:51PM -0800, Song Liu wrote:
>> Introduct new xattr name prefix security.bpf., and enable reading these
>> xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr().
>> 
>> As we are on it, correct the comments for return value of
>> bpf_get_[file|dentry]_xattr(), i.e. return length the xattr value on
>> success.
> 
> Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>

Thanks for the review!

[...]
> 
>> - * Return: 0 on success, a negative value on error.
>> + * Return: length of the xattr value on success, a negative value on error.
>>  */
>> __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
>>     struct bpf_dynptr *value_p)
>> @@ -117,7 +123,9 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
>> if (WARN_ON(!inode))
>> return -EINVAL;
>> 
>> - if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
>> + /* Allow reading xattr with user. and security.bpf. prefix */
>> + if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
>> +    !match_security_bpf_prefix(name__str))
> 
> I think it would be cleaner to have single function
> i.e. is_allowed_xattr_prefix(const char *name__str) which simply
> checks all the allowed xattr prefixes that can be read by this BPF
> kfunc.

Sure, we can add bpf_xattr_read_permission() which pairs with 
bpf_xattr_write_permission(). 

Thanks,
Song

> 
>> return -EPERM;
>> 
>> value_len = __bpf_dynptr_size(value_ptr);
>> @@ -139,9 +147,10 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
>>  *
>>  * Get xattr *name__str* of *file* and store the output in *value_ptr*.
>>  *
>> - * For security reasons, only *name__str* with prefix "user." is allowed.
>> + * For security reasons, only *name__str* with prefix "user." or
>                      ^ prefixes
> 
>> + * "security.bpf." is allowed.
>            ^ are
> 
>> - * Return: 0 on success, a negative value on error.
>> + * Return: length of the xattr value on success, a negative value on error.
>>  */
>> __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
>>   struct bpf_dynptr *value_p)
>> diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
>> index 9854f9cff3c6..c7c85bb504ba 100644
>> --- a/include/uapi/linux/xattr.h
>> +++ b/include/uapi/linux/xattr.h
>> @@ -83,6 +83,10 @@ struct xattr_args {
>> #define XATTR_CAPS_SUFFIX "capability"
>> #define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX
>> 
>> +#define XATTR_BPF_LSM_SUFFIX "bpf."
>> +#define XATTR_NAME_BPF_LSM (XATTR_SECURITY_PREFIX XATTR_BPF_LSM_SUFFIX)
>> +#define XATTR_NAME_BPF_LSM_LEN (sizeof(XATTR_NAME_BPF_LSM) - 1)
>> +
>> #define XATTR_POSIX_ACL_ACCESS  "posix_acl_access"
>> #define XATTR_NAME_POSIX_ACL_ACCESS XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_ACCESS
>> #define XATTR_POSIX_ACL_DEFAULT  "posix_acl_default"
>> -- 
>> 2.43.5
>> 

Re: [PATCH v11 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Alexei Starovoitov]

On Thu, Jan 30, 2025 at 9:49 AM Song Liu <songliubraving@meta.com> wrote:
>
> Hi Alexei,
>
> Thanks for the review!
>
> > On Jan 29, 2025, at 6:32 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>
> [...]
>
> >>
> >> +BTF_ID_LIST(bpf_dynptr_from_skb_list)
> >> +BTF_ID(func, bpf_dynptr_from_skb)
> >> +BTF_ID(func, bpf_dynptr_from_skb_rdonly)
> >> +
> >> +static u32 bpf_kfunc_set_skb_remap(const struct bpf_prog *prog, u32 kfunc_id)
> >> +{
> >> +       if (kfunc_id != bpf_dynptr_from_skb_list[0])
> >> +               return 0;
> >> +
> >> +       switch (resolve_prog_type(prog)) {
> >> +       /* Program types only with direct read access go here! */
> >> +       case BPF_PROG_TYPE_LWT_IN:
> >> +       case BPF_PROG_TYPE_LWT_OUT:
> >> +       case BPF_PROG_TYPE_LWT_SEG6LOCAL:
> >> +       case BPF_PROG_TYPE_SK_REUSEPORT:
> >> +       case BPF_PROG_TYPE_FLOW_DISSECTOR:
> >> +       case BPF_PROG_TYPE_CGROUP_SKB:
> >
> > This copy pastes the logic from may_access_direct_pkt_data(),
> > so any future change to that helper would need to update
> > this one as well.
>
> We can probably improve this with some helpers/macros.
>
> >
> >> +               return bpf_dynptr_from_skb_list[1];
> >
> > The [0] and [1] stuff is quite error prone.
> >
> >> +
> >> +       /* Program types with direct read + write access go here! */
> >> +       case BPF_PROG_TYPE_SCHED_CLS:
> >> +       case BPF_PROG_TYPE_SCHED_ACT:
> >> +       case BPF_PROG_TYPE_XDP:
> >> +       case BPF_PROG_TYPE_LWT_XMIT:
> >> +       case BPF_PROG_TYPE_SK_SKB:
> >> +       case BPF_PROG_TYPE_SK_MSG:
> >> +       case BPF_PROG_TYPE_CGROUP_SOCKOPT:
> >> +               return kfunc_id;
> >> +
> >> +       default:
> >> +               break;
> >> +       }
> >> +       return bpf_dynptr_from_skb_list[1];
> >> +}
> >> +
> >> static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
> >>        .owner = THIS_MODULE,
> >>        .set = &bpf_kfunc_check_set_skb,
> >> +       .hidden_set = &bpf_kfunc_check_hidden_set_skb,
> >
> > If I'm reading it correctly the hidden_set serves no additional purpose.
> > It splits the set into two, but patch 4 just adds them together.
>
> hidden_set does not have BTF_SET8_KFUNCS, so pahole will not export
> these kfuncs to vmlinux.h.
>
> >
> >> +       .remap = &bpf_kfunc_set_skb_remap,
> >
> > I'm not a fan of callbacks in general.
> > The makes everything harder to follow.
>
> This motivation here is to move polymorphism logic from verifier
> core to kfuncs owners. I guess we will need some callback to
> achieve this goal. Of course, we don't have to do it in this set.
>
>
> > For all these reasons I don't like this approach.
> > This "generality" doesn't make it cleaner or easier to extend.
> > For the patch 6... just repeat what specialize_kfunc()
> > currently does for dynptr ?
>
> Yes, specialize_kfunc() can handle this. But we will need to use
> d_inode_locked_hooks from 6/7 in specialize_kfunc(). It works,
> but it is not clean (to me).

I'm missing why that would be necessary to cross the layers
so much. I guess the code will tell.
Pls send an rfc to illustrate the unclean part.

> I will revise this set so that the polymorphism logic in handled
> in specialize_kfunc(). For longer term, maybe we should discuss
> "move some logic from verifier core to kfuncs" in the upcoming
> LSF/MM/BPF?

imo such topic is too narrow and detail oriented.
There is not much to gain from discussing it at lsfmm.
email works well for such discussions.

Re: [PATCH v11 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Song Liu]

> On Jan 30, 2025, at 12:23 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

[...]

>>> For all these reasons I don't like this approach.
>>> This "generality" doesn't make it cleaner or easier to extend.
>>> For the patch 6... just repeat what specialize_kfunc()
>>> currently does for dynptr ?
>> 
>> Yes, specialize_kfunc() can handle this. But we will need to use
>> d_inode_locked_hooks from 6/7 in specialize_kfunc(). It works,
>> but it is not clean (to me).
> 
> I'm missing why that would be necessary to cross the layers
> so much. I guess the code will tell.
> Pls send an rfc to illustrate the unclean part.

The actual code is actually a lot cleaner than I thought. We just
need to use the bpf_lsm_has_d_inode_locked() helper in verifier.c. 

Thanks,
Song

> 
>> I will revise this set so that the polymorphism logic in handled
>> in specialize_kfunc(). For longer term, maybe we should discuss
>> "move some logic from verifier core to kfuncs" in the upcoming
>> LSF/MM/BPF?
> 
> imo such topic is too narrow and detail oriented.
> There is not much to gain from discussing it at lsfmm.
> email works well for such discussions.

Re: [PATCH v11 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

[Matt Bobrowski]

On Thu, Jan 30, 2025 at 04:20:04PM +0100, Christian Brauner wrote:
> On Thu, Jan 30, 2025 at 10:57:35AM +0000, Matt Bobrowski wrote:
> > On Wed, Jan 29, 2025 at 12:59:51PM -0800, Song Liu wrote:
> > > Introduct new xattr name prefix security.bpf., and enable reading these
> > > xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr().
> > > 
> > > As we are on it, correct the comments for return value of
> > > bpf_get_[file|dentry]_xattr(), i.e. return length the xattr value on
> > > success.
> > 
> > Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>
> > 
> > > Signed-off-by: Song Liu <song@kernel.org>
> > > Acked-by: Christian Brauner <brauner@kernel.org>
> > > Reviewed-by: Jan Kara <jack@suse.cz>
> > > ---
> > >  fs/bpf_fs_kfuncs.c         | 19 ++++++++++++++-----
> > >  include/uapi/linux/xattr.h |  4 ++++
> > >  2 files changed, 18 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> > > index 3fe9f59ef867..8a65184c8c2c 100644
> > > --- a/fs/bpf_fs_kfuncs.c
> > > +++ b/fs/bpf_fs_kfuncs.c
> > > @@ -93,6 +93,11 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
> > >  	return len;
> > >  }
> > >  
> > > +static bool match_security_bpf_prefix(const char *name__str)
> > > +{
> > > +	return !strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN);
> > > +}
> > 
> > I think this can also just be match_xattr_prefix(const char
> > *name__str, const char *prefix, size_t len) such that we can do the
> > same checks for aribitrary xattr prefixes i.e. XATTR_USER_PREFIX,
> > XATTR_NAME_BPF_LSM.
> > 
> > >  /**
> > >   * bpf_get_dentry_xattr - get xattr of a dentry
> > >   * @dentry: dentry to get xattr from
> > > @@ -101,9 +106,10 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
> > >   *
> > >   * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
> > >   *
> > > - * For security reasons, only *name__str* with prefix "user." is allowed.
> > > + * For security reasons, only *name__str* with prefix "user." or
> >       	  	   	    	 	     	  ^ prefixes
> > 						  
> > > + * "security.bpf." is allowed.
> >                       ^ are
> > 
> > Out of curiosity, what is the security reasoning here? This isn't
> > obvious to me, and I'd like to understand this better. Is it simply
> > frowned upon to read arbitrary xattr values from the context of a BPF
> > LSM program, or has it got something to do with the backing xattr
> > handler that ends up being called once we step into __vfs_getxattr()
> > and such?  Also, just so that it's clear, I don't have anything
> > against this allow listing approach either, I just genuinely don't
> > understand the security implications.
> 
> I've explained this at lenghts in multiple threads. The gist is various
> xattrs require you to have access to properties that are carried by
> objects you don't have access to (e.g., the mount) or can't guarantee
> that you're in the correct context and interpreting those xattrs without
> this information is either meaningless or actively wrong.

Oh, right, I see. Thank you Christian!