[PATCH bpf-next 1/2] fs/xattr: bpf: Introduce security.bpf xattr name prefix

Song Liu
2024-10-02T21:47:08Z

Introduct new xattr name prefix security.bpf, and enable reading these
xattrs from bpf kfuncs bpf_get_[file|dentry]_xattr(). Note that
"security.bpf" could be the name of the xattr or the prefix of the
name. For example, both "security.bpf" and "security.bpf.xxx" are
valid xattr name; while "security.bpfxxx" is not valid.

Signed-off-by: Song Liu <song@kernel.org>
---
fs/bpf_fs_kfuncs.c | 19 ++++++++++++++++++-
include/uapi/linux/xattr.h | 4 ++++
2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
index 3fe9f59ef867..339c4fef8f6e 100644
--- a/fs/bpf_fs_kfuncs.c
+++ b/fs/bpf_fs_kfuncs.c
@@ -93,6 +93,23 @@ __bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
return len;
}

+static bool bpf_xattr_name_allowed(const char *name__str)
+{
+ /* Allow xattr names with user. prefix */
+ if (!strncmp(name__str, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
+ return true;
+
+ /* Allow security.bpf. prefix or just security.bpf */
+ if (!strncmp(name__str, XATTR_NAME_BPF_LSM, XATTR_NAME_BPF_LSM_LEN) &&
+ (name__str[XATTR_NAME_BPF_LSM_LEN] == '\0' ||
+ name__str[XATTR_NAME_BPF_LSM_LEN] == '.')) {
+ return true;
+ }
+
+ /* Disallow anything else */
+ return false;
+}
+
/**
* bpf_get_dentry_xattr - get xattr of a dentry
* @dentry: dentry to get xattr from
@@ -117,7 +134,7 @@ __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))
+ if (!bpf_xattr_name_allowed(name__str))
return -EPERM;

value_len = __bpf_dynptr_size(value_ptr);
diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
index 9463db2dfa9d..166ef2f1f1b3 100644
--- a/include/uapi/linux/xattr.h
+++ b/include/uapi/linux/xattr.h
@@ -76,6 +76,10 @@
#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