[PATCH v10 bpf-next 1/7] fs/xattr: bpf: Introduce security.bpf. xattr name prefix

Song Liu
2025-01-24T20:29:34Z

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