CIFS: Fix use after free of file info structures

Currently the code assumes that if a file info entry belongs
to lists of open file handles of an inode and a tcon then
it has non-zero reference. The recent changes broke that
assumption when putting the last reference of the file info.
There may be a situation when a file is being deleted but
nothing prevents another thread to reference it again
and start using it. This happens because we do not hold
the inode list lock while checking the number of references
of the file info structure. Fix this by doing the proper
locking when doing the check.

Fixes: 487317c99477d ("cifs: add spinlock for the openFileList to cifsInodeInfo")
Fixes: cb248819d209d ("cifs: use cifsInodeInfo->open_file_lock while iterating to avoid a panic")
Cc: Stable <stable@vger.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 5ad15de2bb4f950cf88d72f3d15b3b3132e72bcd..64827938ecf75825f5e61a3fc663d887dd40c1ef 100644 (file)
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -405,10 +405,11 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
        bool oplock_break_cancelled;
 
        spin_lock(&tcon->open_file_lock);
-
+       spin_lock(&cifsi->open_file_lock);
        spin_lock(&cifs_file->file_info_lock);
        if (--cifs_file->count > 0) {
                spin_unlock(&cifs_file->file_info_lock);
+               spin_unlock(&cifsi->open_file_lock);
                spin_unlock(&tcon->open_file_lock);
                return;
        }
@@ -421,9 +422,7 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
        cifs_add_pending_open_locked(&fid, cifs_file->tlink, &open);
 
        /* remove it from the lists */
-       spin_lock(&cifsi->open_file_lock);
        list_del(&cifs_file->flist);
-       spin_unlock(&cifsi->open_file_lock);
        list_del(&cifs_file->tlist);
        atomic_dec(&tcon->num_local_opens);
 
@@ -440,6 +439,7 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
                cifs_set_oplock_level(cifsi, 0);
        }
 
+       spin_unlock(&cifsi->open_file_lock);
        spin_unlock(&tcon->open_file_lock);
 
        oplock_break_cancelled = wait_oplock_handler ?