cifs: fix dentry refcount leak when opening a FIFO on lookup

The cifs code will attempt to open files on lookup under certain
circumstances. What happens though if we find that the file we opened
was actually a FIFO or other special file?

Currently, the open filehandle just ends up being leaked leading to
a dentry refcount mismatch and oops on umount. Fix this by having the
code close the filehandle on the server if it turns out not to be a
regular file. While we're at it, change this spaghetti if statement
into a switch too.

Cc: stable@vger.kernel.org
Reported-by: CAI Qian <caiqian@redhat.com>
Tested-by: CAI Qian <caiqian@redhat.com>
Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 18 insertions, 2 deletions

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index 63a196b97d50..bc7e24420ac0 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -584,10 +584,26 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
                          * If either that or op not supported returned, follow
                          * the normal lookup.
                          */
-                        if ((rc == 0) || (rc == -ENOENT))
+                        switch (rc) {
+                        case 0:
+                                /*
+                                 * The server may allow us to open things like
+                                 * FIFOs, but the client isn't set up to deal
+                                 * with that. If it's not a regular file, just
+                                 * close it and proceed as if it were a normal
+                                 * lookup.
+                                 */
+                                if (newInode && !S_ISREG(newInode->i_mode)) {
+                                        CIFSSMBClose(xid, pTcon, fileHandle);
+                                        break;
+                                }
+                        case -ENOENT:
                                 posix_open = true;
-                        else if ((rc == -EINVAL) || (rc != -EOPNOTSUPP))
+                        case -EOPNOTSUPP:
+                                break;
+                        default:
                                 pTcon->broken_posix_open = true;
+                        }
                 }
                 if (!posix_open)
                         rc = cifs_get_inode_info_unix(&newInode, full_path,