[PATCH v2 bpf-next 0/2] Add bpf_get_dentry_xattr

[PATCH v2 bpf-next 0/2] Add bpf_get_dentry_xattr

[Song Liu]

Add a kfunc to read xattr from dentry. Also add selftest for the new
kfunc.


Changes v1 => v2:
1. Remove 3 kfuncs that are ready yet.

v1: https://lore.kernel.org/linux-fsdevel/20240725234706.655613-1-song@kernel.org/T/#u

Song Liu (2):
  bpf: Add kfunc bpf_get_dentry_xattr() to read xattr from dentry
  selftests/bpf: Add tests for bpf_get_dentry_xattr

 kernel/trace/bpf_trace.c                      | 46 ++++++++++++++-----
 .../selftests/bpf/prog_tests/fs_kfuncs.c      |  9 +++-
 .../selftests/bpf/progs/test_get_xattr.c      | 37 +++++++++++++--
 3 files changed, 75 insertions(+), 17 deletions(-)

--
2.43.0

[PATCH v2 bpf-next 1/2] bpf: Add kfunc bpf_get_dentry_xattr() to read xattr from dentry

[Song Liu]

This kfunc can be used in LSM hooks with dentry, such as:

  security_inode_listxattr
  security_inode_permission

and many more.

Signed-off-by: Song Liu <song@kernel.org>
---
 kernel/trace/bpf_trace.c | 46 ++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index cd098846e251..c62a00975f92 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1443,26 +1443,29 @@ late_initcall(bpf_key_sig_kfuncs_init);
 __bpf_kfunc_start_defs();
 
 /**
- * bpf_get_file_xattr - get xattr of a file
- * @file: file to get xattr from
+ * bpf_get_dentry_xattr - get xattr of a dentry
+ * @dentry: dentry to get xattr from
  * @name__str: name of the xattr
  * @value_p: output buffer of the xattr value
  *
- * Get xattr *name__str* of *file* and store the output in *value_ptr*.
+ * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
  *
  * For security reasons, only *name__str* with prefix "user." is allowed.
  *
  * Return: 0 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)
+__bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
+				     struct bpf_dynptr *value_p)
 {
 	struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
-	struct dentry *dentry;
+	struct inode *inode = d_inode(dentry);
 	u32 value_len;
 	void *value;
 	int ret;
 
+	if (WARN_ON(!inode))
+		return -EINVAL;
+
 	if (strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
 		return -EPERM;
 
@@ -1471,20 +1474,41 @@ __bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
 	if (!value)
 		return -EINVAL;
 
-	dentry = file_dentry(file);
-	ret = inode_permission(&nop_mnt_idmap, dentry->d_inode, MAY_READ);
+	ret = inode_permission(&nop_mnt_idmap, inode, MAY_READ);
 	if (ret)
 		return ret;
-	return __vfs_getxattr(dentry, dentry->d_inode, name__str, value, value_len);
+	return __vfs_getxattr(dentry, inode, name__str, value, value_len);
+}
+
+/**
+ * bpf_get_file_xattr - get xattr of a file
+ * @file: file to get xattr from
+ * @name__str: name of the xattr
+ * @value_p: output buffer of the xattr value
+ *
+ * Get xattr *name__str* of *file* and store the output in *value_ptr*.
+ *
+ * For security reasons, only *name__str* with prefix "user." is allowed.
+ *
+ * Return: 0 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)
+{
+	struct dentry *dentry;
+
+	dentry = file_dentry(file);
+	return bpf_get_dentry_xattr(dentry, name__str, value_p);
 }
 
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(fs_kfunc_set_ids)
+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_KFUNCS_END(fs_kfunc_set_ids)
 
-static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id)
+static int fs_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id)
 {
 	if (!btf_id_set8_contains(&fs_kfunc_set_ids, kfunc_id))
 		return 0;
@@ -1496,7 +1520,7 @@ static int bpf_get_file_xattr_filter(const struct bpf_prog *prog, u32 kfunc_id)
 static const struct btf_kfunc_id_set bpf_fs_kfunc_set = {
 	.owner = THIS_MODULE,
 	.set = &fs_kfunc_set_ids,
-	.filter = bpf_get_file_xattr_filter,
+	.filter = fs_kfunc_filter,
 };
 
 static int __init bpf_fs_kfuncs_init(void)
-- 
2.43.0

[PATCH v2 bpf-next 2/2] selftests/bpf: Add tests for bpf_get_dentry_xattr

[Song Liu]

Add test for bpf_get_dentry_xattr on hook security_inode_getxattr.
Verify that the kfunc can read the xattr. Also test failing getxattr
from user space by returning non-zero from the LSM bpf program.

Signed-off-by: Song Liu <song@kernel.org>
---
 .../selftests/bpf/prog_tests/fs_kfuncs.c      |  9 ++++-
 .../selftests/bpf/progs/test_get_xattr.c      | 37 ++++++++++++++++---
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 37056ba73847..5a0b51157451 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -16,6 +16,7 @@ static void test_xattr(void)
 {
 	struct test_get_xattr *skel = NULL;
 	int fd = -1, err;
+	int v[32];
 
 	fd = open(testfile, O_CREAT | O_RDONLY, 0644);
 	if (!ASSERT_GE(fd, 0, "create_file"))
@@ -50,7 +51,13 @@ static void test_xattr(void)
 	if (!ASSERT_GE(fd, 0, "open_file"))
 		goto out;
 
-	ASSERT_EQ(skel->bss->found_xattr, 1, "found_xattr");
+	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");
 
 out:
 	close(fd);
diff --git a/tools/testing/selftests/bpf/progs/test_get_xattr.c b/tools/testing/selftests/bpf/progs/test_get_xattr.c
index 7eb2a4e5a3e5..66e737720f7c 100644
--- a/tools/testing/selftests/bpf/progs/test_get_xattr.c
+++ b/tools/testing/selftests/bpf/progs/test_get_xattr.c
@@ -2,6 +2,7 @@
 /* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
 
 #include "vmlinux.h"
+#include <errno.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 #include "bpf_kfuncs.h"
@@ -9,10 +10,12 @@
 char _license[] SEC("license") = "GPL";
 
 __u32 monitored_pid;
-__u32 found_xattr;
+__u32 found_xattr_from_file;
+__u32 found_xattr_from_dentry;
 
 static const char expected_value[] = "hello";
-char value[32];
+char value1[32];
+char value2[32];
 
 SEC("lsm.s/file_open")
 int BPF_PROG(test_file_open, struct file *f)
@@ -25,13 +28,37 @@ int BPF_PROG(test_file_open, struct file *f)
 	if (pid != monitored_pid)
 		return 0;
 
-	bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
+	bpf_dynptr_from_mem(value1, sizeof(value1), 0, &value_ptr);
 
 	ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
 	if (ret != sizeof(expected_value))
 		return 0;
-	if (bpf_strncmp(value, ret, expected_value))
+	if (bpf_strncmp(value1, ret, expected_value))
 		return 0;
-	found_xattr = 1;
+	found_xattr_from_file = 1;
 	return 0;
 }
+
+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;
+
+	bpf_dynptr_from_mem(value2, sizeof(value2), 0, &value_ptr);
+
+	ret = bpf_get_dentry_xattr(dentry, "user.kfuncs", &value_ptr);
+	if (ret != sizeof(expected_value))
+		return 0;
+	if (bpf_strncmp(value2, ret, expected_value))
+		return 0;
+	found_xattr_from_dentry = 1;
+
+	/* return non-zero to fail getxattr from user space */
+	return -EINVAL;
+}
-- 
2.43.0

Re: [PATCH v2 bpf-next 0/2] Add bpf_get_dentry_xattr

[Christian Brauner]

On Tue, Jul 30, 2024 at 04:08:03PM GMT, Song Liu wrote:
> Add a kfunc to read xattr from dentry. Also add selftest for the new
> kfunc.

Looks ok to me now,
Acked-by: Christian Brauner <brauner@kernel.org>

Re: [PATCH v2 bpf-next 2/2] selftests/bpf: Add tests for bpf_get_dentry_xattr

[Alexei Starovoitov]

On Tue, Jul 30, 2024 at 4:08 PM Song Liu <song@kernel.org> wrote:
>
> Add test for bpf_get_dentry_xattr on hook security_inode_getxattr.
> Verify that the kfunc can read the xattr. Also test failing getxattr
> from user space by returning non-zero from the LSM bpf program.
>
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  .../selftests/bpf/prog_tests/fs_kfuncs.c      |  9 ++++-
>  .../selftests/bpf/progs/test_get_xattr.c      | 37 ++++++++++++++++---
>  2 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
> index 37056ba73847..5a0b51157451 100644
> --- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
> +++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
> @@ -16,6 +16,7 @@ static void test_xattr(void)
>  {
>         struct test_get_xattr *skel = NULL;
>         int fd = -1, err;
> +       int v[32];
>
>         fd = open(testfile, O_CREAT | O_RDONLY, 0644);
>         if (!ASSERT_GE(fd, 0, "create_file"))
> @@ -50,7 +51,13 @@ static void test_xattr(void)
>         if (!ASSERT_GE(fd, 0, "open_file"))
>                 goto out;
>
> -       ASSERT_EQ(skel->bss->found_xattr, 1, "found_xattr");
> +       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");
>
>  out:
>         close(fd);
> diff --git a/tools/testing/selftests/bpf/progs/test_get_xattr.c b/tools/testing/selftests/bpf/progs/test_get_xattr.c
> index 7eb2a4e5a3e5..66e737720f7c 100644
> --- a/tools/testing/selftests/bpf/progs/test_get_xattr.c
> +++ b/tools/testing/selftests/bpf/progs/test_get_xattr.c
> @@ -2,6 +2,7 @@
>  /* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
>
>  #include "vmlinux.h"
> +#include <errno.h>
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
>  #include "bpf_kfuncs.h"
> @@ -9,10 +10,12 @@
>  char _license[] SEC("license") = "GPL";
>
>  __u32 monitored_pid;
> -__u32 found_xattr;
> +__u32 found_xattr_from_file;
> +__u32 found_xattr_from_dentry;
>
>  static const char expected_value[] = "hello";
> -char value[32];
> +char value1[32];
> +char value2[32];
>
>  SEC("lsm.s/file_open")
>  int BPF_PROG(test_file_open, struct file *f)
> @@ -25,13 +28,37 @@ int BPF_PROG(test_file_open, struct file *f)
>         if (pid != monitored_pid)
>                 return 0;
>
> -       bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
> +       bpf_dynptr_from_mem(value1, sizeof(value1), 0, &value_ptr);
>
>         ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
>         if (ret != sizeof(expected_value))
>                 return 0;
> -       if (bpf_strncmp(value, ret, expected_value))
> +       if (bpf_strncmp(value1, ret, expected_value))
>                 return 0;
> -       found_xattr = 1;
> +       found_xattr_from_file = 1;
>         return 0;
>  }
> +
> +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;
> +
> +       bpf_dynptr_from_mem(value2, sizeof(value2), 0, &value_ptr);
> +
> +       ret = bpf_get_dentry_xattr(dentry, "user.kfuncs", &value_ptr);

Song,

See CI failure on s390.
I think you need to update bpf_kfuncs.h, since s390 doesn't emit
kfuncs into vmlinux.h

Also pls add a patch to move these kfuncs to fs/bpf_fs_kfuncs.c

pw-bot: cr