[PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout

From: Mark Salyzyn
Date: Tue Aug 28 2018 - 12:53:26 EST

Assumption never checked, should fail if the mounter creds are not

Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
Cc: linux-unionfs@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx

- dependency of "overlayfs: override_creds=off option bypass creator_cred"
fs/overlayfs/overlayfs.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 7538b9b56237..bf3a80157d42 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,

static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
- int err = vfs_whiteout(dir, dentry);
+ int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
pr_debug("whiteout(%pd2) = %i\n", dentry, err);
return err;