cifs: when renaming don't try to unlink negative dentry

When attempting to rename a file on a read-only share, the kernel can
call cifs_unlink on a negative dentry, which causes an oops. Only try
to unlink the file if it's a positive dentry.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Shirish Pargaonkar <shirishp@us.ibm.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index 09082ac85185..f36b4e40e443 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -1453,7 +1453,8 @@ int cifs_rename(struct inode *source_dir, struct dentry *source_dentry,
                      checking the UniqueId via FILE_INTERNAL_INFO */
 
 unlink_target:
-        if ((rc == -EACCES) || (rc == -EEXIST)) {
+        /* Try unlinking the target dentry if it's not negative */
+        if (target_dentry->d_inode && (rc == -EACCES || rc == -EEXIST)) {
                 tmprc = cifs_unlink(target_dir, target_dentry);
                 if (tmprc)
                         goto cifs_rename_exit;