cifs: Replace wrtPending with a real reference count

Currently, cifs_close() tries to wait until all I/O is complete and then
frees the file private data.  If I/O does not completely in a reasonable
amount of time it frees the structure anyway, leaving a potential use-
after-free situation.

This patch changes the wrtPending counter to a complete reference count and
lets the last user free the structure.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index f100399ee05e..6cfc81a32703 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -351,11 +351,24 @@ struct cifsFileInfo {
         bool closePend:1;       /* file is marked to close */
         bool invalidHandle:1;   /* file closed via session abend */
         bool messageMode:1;     /* for pipes: message vs byte mode */
-        atomic_t wrtPending;   /* handle in use - defer close */
+        atomic_t count;         /* reference count */
         struct mutex fh_mutex; /* prevents reopen race after dead ses*/
         struct cifs_search_info srch_inf;
 };
 
+/* Take a reference on the file private data */
+static inline void cifsFileInfo_get(struct cifsFileInfo *cifs_file)
+{
+        atomic_inc(&cifs_file->count);
+}
+
+/* Release a reference on the file private data */
+static inline void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
+{
+        if (atomic_dec_and_test(&cifs_file->count))
+                kfree(cifs_file);
+}
+
 /*
  * One of these for each file inode
  */