cifs: fix potential use-after-free in cifs_oplock_break_put

cfile may very well be freed after the cifsFileInfo_put. Make sure we
have a valid pointer to the superblock for cifs_sb_deactive.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 06c3e83fa387..b857ce5db775 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2271,8 +2271,10 @@ void cifs_oplock_break_get(struct cifsFileInfo *cfile)
 
 void cifs_oplock_break_put(struct cifsFileInfo *cfile)
 {
+        struct super_block *sb = cfile->dentry->d_sb;
+
         cifsFileInfo_put(cfile);
-        cifs_sb_deactive(cfile->dentry->d_sb);
+        cifs_sb_deactive(sb);
 }
 
 const struct address_space_operations cifs_addr_ops = {