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* [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs
@ 2025-01-30 21:35 Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 1/5] fs/xattr: bpf: Introduce security.bpf. xattr name prefix Song Liu
                   ` (4 more replies)
  0 siblings, 5 replies; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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 v11 => v12:
1. Drop btf_kfunc_id_set.remap and changes for bpf_dynptr_from_skb.
   (Alexei)
2. Minor refactoring in patch 1. (Matt Bobrowski)

v11: https://lore.kernel.org/bpf/20250129205957.2457655-1-song@kernel.org/

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 (5):
  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: 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                            | 225 +++++++++++++++++-
 include/linux/bpf_lsm.h                       |  18 ++
 include/uapi/linux/xattr.h                    |   4 +
 kernel/bpf/bpf_lsm.c                          |   2 +
 kernel/bpf/verifier.c                         |  21 ++
 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 +++++++++++
 9 files changed, 573 insertions(+), 25 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_set_remove_xattr.c

--
2.43.5

^ permalink raw reply	[flat|nested] 8+ messages in thread
* [PATCH v12 bpf-next 1/5] fs/xattr: bpf: Introduce security.bpf. xattr name prefix
  2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
@ 2025-01-30 21:35 ` Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 2/5] selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names Song Liu
                   ` (3 subsequent siblings)
  4 siblings, 0 replies; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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>
Reviewed-by: Matt Bobrowski <mattbobrowski@google.com>
---
 fs/bpf_fs_kfuncs.c         | 36 +++++++++++++++++++++++++-----------
 include/uapi/linux/xattr.h |  4 ++++
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 3fe9f59ef867..db5c8e855517 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -93,6 +93,24 @@ __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);
+}
+
+static int bpf_xattr_read_permission(const char *name, struct inode *inode)
+{
+	if (WARN_ON(!inode))
+		return -EINVAL;
+
+	/* Allow reading xattr with user. and security.bpf. prefix */
+	if (strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
+	    !match_security_bpf_prefix(name))
+		return -EPERM;
+
+	return inode_permission(&nop_mnt_idmap, inode, MAY_READ);
+}
+
 /**
  * bpf_get_dentry_xattr - get xattr of a dentry
  * @dentry: dentry to get xattr from
@@ -101,9 +119,10 @@ __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 prefixes "user." or
+ * "security.bpf." are 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)
@@ -114,18 +133,12 @@ __bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__st
 	void *value;
 	int ret;
 
-	if (WARN_ON(!inode))
-		return -EINVAL;
-
-	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
-		return -EPERM;
-
 	value_len = __bpf_dynptr_size(value_ptr);
 	value = __bpf_dynptr_data_rw(value_ptr, value_len);
 	if (!value)
 		return -EINVAL;
 
-	ret = inode_permission(&nop_mnt_idmap, inode, MAY_READ);
+	ret = bpf_xattr_read_permission(name__str, inode);
 	if (ret)
 		return ret;
 	return __vfs_getxattr(dentry, inode, name__str, value, value_len);
@@ -139,9 +152,10 @@ __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 prefixes "user." or
+ * "security.bpf." are 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


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* [PATCH v12 bpf-next 2/5] selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names
  2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 1/5] fs/xattr: bpf: Introduce security.bpf. xattr name prefix Song Liu
@ 2025-01-30 21:35 ` Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks Song Liu
                   ` (2 subsequent siblings)
  4 siblings, 0 replies; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks
  2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 1/5] fs/xattr: bpf: Introduce security.bpf. xattr name prefix Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 2/5] selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names Song Liu
@ 2025-01-30 21:35 ` Song Liu
  2025-01-31  8:40   ` Matt Bobrowski
  2025-01-30 21:35 ` [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs Song Liu
  2025-01-30 21:35 ` [PATCH v12 bpf-next 5/5] selftests/bpf: Test kfuncs that set and remove xattr from BPF programs Song Liu
  4 siblings, 1 reply; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs
  2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
                   ` (2 preceding siblings ...)
  2025-01-30 21:35 ` [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks Song Liu
@ 2025-01-30 21:35 ` Song Liu
  2025-01-31  9:10   ` Matt Bobrowski
  2025-01-30 21:35 ` [PATCH v12 bpf-next 5/5] selftests/bpf: Test kfuncs that set and remove xattr from BPF programs Song Liu
  4 siblings, 1 reply; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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      | 189 ++++++++++++++++++++++++++++++++++++++++
 include/linux/bpf_lsm.h |  18 ++++
 kernel/bpf/verifier.c   |  21 +++++
 3 files changed, 228 insertions(+)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index db5c8e855517..08412532db1b 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>
@@ -168,6 +170,160 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
 
 __bpf_kfunc_end_defs();
 
+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.
+ */
+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_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.
+ */
+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_kfunc_start_defs();
+
+/**
+ * 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 - 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)
 BTF_ID_FLAGS(func, bpf_get_task_exe_file,
 	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
@@ -175,6 +331,8 @@ 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)
 
 static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
@@ -185,6 +343,37 @@ static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
 	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)
+
+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);
+}
+
 static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
 	.owner = THIS_MODULE,
 	.set = &bpf_fs_kfunc_set_ids,
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index aefcd6564251..643809cc78c3 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -48,6 +48,11 @@ 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);
+int bpf_set_dentry_xattr_locked(struct dentry *dentry, const char *name__str,
+				const struct bpf_dynptr *value_p, int flags);
+int bpf_remove_dentry_xattr_locked(struct dentry *dentry, const char *name__str);
+bool bpf_lsm_has_d_inode_locked(const struct bpf_prog *prog);
+
 #else /* !CONFIG_BPF_LSM */
 
 static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
@@ -86,6 +91,19 @@ static inline int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
 {
 	return -EOPNOTSUPP;
 }
+static inline int bpf_set_dentry_xattr_locked(struct dentry *dentry, const char *name__str,
+					      const struct bpf_dynptr *value_p, int flags)
+{
+	return -EOPNOTSUPP;
+}
+static inline int bpf_remove_dentry_xattr_locked(struct dentry *dentry, const char *name__str)
+{
+	return -EOPNOTSUPP;
+}
+static inline bool bpf_lsm_has_d_inode_locked(const struct bpf_prog *prog)
+{
+	return false;
+}
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03adfd5..04d1d75d9ff9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11766,6 +11766,8 @@ enum special_kfunc_type {
 	KF_bpf_iter_num_new,
 	KF_bpf_iter_num_next,
 	KF_bpf_iter_num_destroy,
+	KF_bpf_set_dentry_xattr,
+	KF_bpf_remove_dentry_xattr,
 };
 
 BTF_SET_START(special_kfunc_set)
@@ -11795,6 +11797,10 @@ BTF_ID(func, bpf_wq_set_callback_impl)
 #ifdef CONFIG_CGROUPS
 BTF_ID(func, bpf_iter_css_task_new)
 #endif
+#ifdef CONFIG_BPF_LSM
+BTF_ID(func, bpf_set_dentry_xattr)
+BTF_ID(func, bpf_remove_dentry_xattr)
+#endif
 BTF_SET_END(special_kfunc_set)
 
 BTF_ID_LIST(special_kfunc_list)
@@ -11844,6 +11850,13 @@ BTF_ID(func, bpf_local_irq_restore)
 BTF_ID(func, bpf_iter_num_new)
 BTF_ID(func, bpf_iter_num_next)
 BTF_ID(func, bpf_iter_num_destroy)
+#ifdef CONFIG_BPF_LSM
+BTF_ID(func, bpf_set_dentry_xattr)
+BTF_ID(func, bpf_remove_dentry_xattr)
+#else
+BTF_ID_UNUSED
+BTF_ID_UNUSED
+#endif
 
 static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
 {
@@ -20924,6 +20937,14 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
 		 */
 		env->seen_direct_write = seen_direct_write;
 	}
+
+	if (func_id == special_kfunc_list[KF_bpf_set_dentry_xattr] &&
+	    bpf_lsm_has_d_inode_locked(prog))
+		*addr = (unsigned long)bpf_set_dentry_xattr_locked;
+
+	if (func_id == special_kfunc_list[KF_bpf_remove_dentry_xattr] &&
+	    bpf_lsm_has_d_inode_locked(prog))
+		*addr = (unsigned long)bpf_remove_dentry_xattr_locked;
 }
 
 static void __fixup_collection_insert_kfunc(struct bpf_insn_aux_data *insn_aux,
-- 
2.43.5


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* [PATCH v12 bpf-next 5/5] selftests/bpf: Test kfuncs that set and remove xattr from BPF programs
  2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
                   ` (3 preceding siblings ...)
  2025-01-30 21:35 ` [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs Song Liu
@ 2025-01-30 21:35 ` Song Liu
  4 siblings, 0 replies; 8+ messages in thread
From: Song Liu @ 2025-01-30 21:35 UTC (permalink / raw)
  To: bpf, linux-fsdevel, linux-kernel, linux-security-module
  Cc: kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, mattbobrowski, liamwisehart, shankaran,
	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


^ permalink raw reply related	[flat|nested] 8+ messages in thread
* Re: [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks
  2025-01-30 21:35 ` [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks Song Liu
@ 2025-01-31  8:40   ` Matt Bobrowski
  0 siblings, 0 replies; 8+ messages in thread
From: Matt Bobrowski @ 2025-01-31  8:40 UTC (permalink / raw)
  To: Song Liu
  Cc: bpf, linux-fsdevel, linux-kernel, linux-security-module,
	kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, liamwisehart, shankaran

On Thu, Jan 30, 2025 at 01:35:47PM -0800, Song Liu wrote:
> 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.

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

> 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
> 

^ permalink raw reply	[flat|nested] 8+ messages in thread
* Re: [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs
  2025-01-30 21:35 ` [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs Song Liu
@ 2025-01-31  9:10   ` Matt Bobrowski
  0 siblings, 0 replies; 8+ messages in thread
From: Matt Bobrowski @ 2025-01-31  9:10 UTC (permalink / raw)
  To: Song Liu
  Cc: bpf, linux-fsdevel, linux-kernel, linux-security-module,
	kernel-team, andrii, eddyz87, ast, daniel, martin.lau, viro,
	brauner, jack, kpsingh, liamwisehart, shankaran

On Thu, Jan 30, 2025 at 01:35:48PM -0800, Song Liu wrote:
> 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.

Looks good to me, thank you for working on this!

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

> Signed-off-by: Song Liu <song@kernel.org>
> Acked-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/bpf_fs_kfuncs.c      | 189 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/bpf_lsm.h |  18 ++++
>  kernel/bpf/verifier.c   |  21 +++++
>  3 files changed, 228 insertions(+)
> 
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index db5c8e855517..08412532db1b 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>
> @@ -168,6 +170,160 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
>  
>  __bpf_kfunc_end_defs();
>  
> +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.
> + */

Should we also make a remark about what `flags` corresponds to
i.e. `flags` which are passed into the *setxattr(2) set of system
calls?

> +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_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.
> + */
> +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_kfunc_start_defs();
> +
> +/**
> + * 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 - 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)
>  BTF_ID_FLAGS(func, bpf_get_task_exe_file,
>  	     KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
> @@ -175,6 +331,8 @@ 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)
>  
>  static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
> @@ -185,6 +343,37 @@ static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
>  	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)
> +
> +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);
> +}
> +
>  static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
>  	.owner = THIS_MODULE,
>  	.set = &bpf_fs_kfunc_set_ids,
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index aefcd6564251..643809cc78c3 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -48,6 +48,11 @@ 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);
> +int bpf_set_dentry_xattr_locked(struct dentry *dentry, const char *name__str,
> +				const struct bpf_dynptr *value_p, int flags);
> +int bpf_remove_dentry_xattr_locked(struct dentry *dentry, const char *name__str);
> +bool bpf_lsm_has_d_inode_locked(const struct bpf_prog *prog);
> +
>  #else /* !CONFIG_BPF_LSM */
>  
>  static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
> @@ -86,6 +91,19 @@ static inline int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
>  {
>  	return -EOPNOTSUPP;
>  }
> +static inline int bpf_set_dentry_xattr_locked(struct dentry *dentry, const char *name__str,
> +					      const struct bpf_dynptr *value_p, int flags)
> +{
> +	return -EOPNOTSUPP;
> +}
> +static inline int bpf_remove_dentry_xattr_locked(struct dentry *dentry, const char *name__str)
> +{
> +	return -EOPNOTSUPP;
> +}
> +static inline bool bpf_lsm_has_d_inode_locked(const struct bpf_prog *prog)
> +{
> +	return false;
> +}
>  #endif /* CONFIG_BPF_LSM */
>  
>  #endif /* _LINUX_BPF_LSM_H */
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9971c03adfd5..04d1d75d9ff9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -11766,6 +11766,8 @@ enum special_kfunc_type {
>  	KF_bpf_iter_num_new,
>  	KF_bpf_iter_num_next,
>  	KF_bpf_iter_num_destroy,
> +	KF_bpf_set_dentry_xattr,
> +	KF_bpf_remove_dentry_xattr,
>  };
>  
>  BTF_SET_START(special_kfunc_set)
> @@ -11795,6 +11797,10 @@ BTF_ID(func, bpf_wq_set_callback_impl)
>  #ifdef CONFIG_CGROUPS
>  BTF_ID(func, bpf_iter_css_task_new)
>  #endif
> +#ifdef CONFIG_BPF_LSM
> +BTF_ID(func, bpf_set_dentry_xattr)
> +BTF_ID(func, bpf_remove_dentry_xattr)
> +#endif
>  BTF_SET_END(special_kfunc_set)
>  
>  BTF_ID_LIST(special_kfunc_list)
> @@ -11844,6 +11850,13 @@ BTF_ID(func, bpf_local_irq_restore)
>  BTF_ID(func, bpf_iter_num_new)
>  BTF_ID(func, bpf_iter_num_next)
>  BTF_ID(func, bpf_iter_num_destroy)
> +#ifdef CONFIG_BPF_LSM
> +BTF_ID(func, bpf_set_dentry_xattr)
> +BTF_ID(func, bpf_remove_dentry_xattr)
> +#else
> +BTF_ID_UNUSED
> +BTF_ID_UNUSED
> +#endif
>  
>  static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
>  {
> @@ -20924,6 +20937,14 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
>  		 */
>  		env->seen_direct_write = seen_direct_write;
>  	}
> +
> +	if (func_id == special_kfunc_list[KF_bpf_set_dentry_xattr] &&
> +	    bpf_lsm_has_d_inode_locked(prog))
> +		*addr = (unsigned long)bpf_set_dentry_xattr_locked;
> +
> +	if (func_id == special_kfunc_list[KF_bpf_remove_dentry_xattr] &&
> +	    bpf_lsm_has_d_inode_locked(prog))
> +		*addr = (unsigned long)bpf_remove_dentry_xattr_locked;
>  }
>  
>  static void __fixup_collection_insert_kfunc(struct bpf_insn_aux_data *insn_aux,
> -- 
> 2.43.5
> 

^ permalink raw reply	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2025-01-31  9:10 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-01-30 21:35 [PATCH v12 bpf-next 0/5] Enable writing xattr from BPF programs Song Liu
2025-01-30 21:35 ` [PATCH v12 bpf-next 1/5] fs/xattr: bpf: Introduce security.bpf. xattr name prefix Song Liu
2025-01-30 21:35 ` [PATCH v12 bpf-next 2/5] selftests/bpf: Extend test fs_kfuncs to cover security.bpf. xattr names Song Liu
2025-01-30 21:35 ` [PATCH v12 bpf-next 3/5] bpf: lsm: Add two more sleepable hooks Song Liu
2025-01-31  8:40   ` Matt Bobrowski
2025-01-30 21:35 ` [PATCH v12 bpf-next 4/5] bpf: fs/xattr: Add BPF kfuncs to set and remove xattrs Song Liu
2025-01-31  9:10   ` Matt Bobrowski
2025-01-30 21:35 ` [PATCH v12 bpf-next 5/5] selftests/bpf: Test kfuncs that set and remove xattr from BPF programs Song Liu

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