======== ========
inv_file = NULL
refind = 0
spin_lock(&cifs_file_list_lock)
// invalidHandle found on openFileList
inv_file = open_file
// inv_file->count currently 1
cifsFileInfo_get(inv_file)
// inv_file->count = 2
spin_unlock(&cifs_file_list_lock);
cifs_reopen_file() cifs_close()
// fails (rc != 0) ->cifsFileInfo_put()
spin_lock(&cifs_file_list_lock)
// inv_file->count = 1
spin_unlock(&cifs_file_list_lock)
spin_lock(&cifs_file_list_lock);
list_move_tail(&inv_file->flist,
&cifs_inode->openFileList);
spin_unlock(&cifs_file_list_lock);
cifsFileInfo_put(inv_file);
->spin_lock(&cifs_file_list_lock)
// inv_file->count = 0
list_del(&cifs_file->flist);
// cleanup!!
kfree(cifs_file);
spin_unlock(&cifs_file_list_lock);
spin_lock(&cifs_file_list_lock);
++refind;
// refind = 1
goto refind_writable;
At this point we loop back through with an invalid inv_file pointer
and a refind value of 1. On second pass, inv_file is not overwritten on
openFileList traversal, and is subsequently dereferenced.
Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Jeff Layton <jlayton@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/cifs/file.c | 1 +
1 file changed, 1 insertion(+)
@@ -1821,6 +1821,7 @@ refind_writable:
cifsFileInfo_put(inv_file);
spin_lock(&cifs_file_list_lock);
++refind;
+ inv_file = NULL;
goto refind_writable;
}
}
3.13.11-ckt20 -stable review patch. If anyone has any objections, please let me know. ------------------ From: David Disseldorp <ddiss@suse.de> commit e1e9bda22d7ddf88515e8fe401887e313922823e upstream. Under intermittent network outages, find_writable_file() is susceptible to the following race condition, which results in a user-after-free in the cifs_writepages code-path: Thread 1 Thread 2