[PATCH] overlayfs: filter of trusted xattr results in audit.

From: Mark Salyzyn
Date: Thu Aug 29 2019 - 14:30:34 EST

When filtering xattr list for reading, presence of trusted xattr
results in a security audit log. However, if there is other content
no errno will be set, and if there isn't, the errno will be -ENODATA
and not -EPERM as is usually associated with a lack of capability.
The check does not block the request to list the xattrs present.

Switch to ns_capable_noaudit to reflect a more appropriate check.

Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxxx
Cc: linux-security-module@xxxxxxxxxxxxxxx
Cc: kernel-team@xxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # 4.4, 4.9, 4.14 & 4.19
fs/overlayfs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 7663aeb85fa3..bc14781886bf 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -383,7 +383,8 @@ static bool ovl_can_list(const char *s)
return true;

/* Never list trusted.overlay, list other trusted for superuser only */
- return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
+ return !ovl_is_private_xattr(s) &&
+ ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);

ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)