From e1e9bda22d7ddf88515e8fe401887e313922823e Mon Sep 17 00:00:00 2001 From: David Disseldorp Date: Fri, 13 Mar 2015 14:20:29 +0100 Subject: [PATCH] cifs: fix use-after-free bug in find_writable_file 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 ======== ======== 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 Reviewed-by: Jeff Layton CC: Signed-off-by: Steve French --- fs/cifs/file.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/cifs/file.c b/fs/cifs/file.c index a94b3e673182..ca30c391a894 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -1823,6 +1823,7 @@ refind_writable: cifsFileInfo_put(inv_file); spin_lock(&cifs_file_list_lock); ++refind; + inv_file = NULL; goto refind_writable; } } -- 2.20.1