From: David Disseldorp Date: Fri, 13 Mar 2015 13:20:29 +0000 (+0100) Subject: cifs: fix use-after-free bug in find_writable_file X-Git-Tag: omap-for-v4.1/fixes-rc1~235^2~9 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e1e9bda22d7ddf88515e8fe401887e313922823e;p=pandora-kernel.git 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 --- Reading git-diff-tree failed