From: Eric Paris Date: Tue, 11 May 2010 21:17:40 +0000 (-0400) Subject: inotify: race use after free/double free in inotify inode marks X-Git-Tag: v2.6.34~13^2~1 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=e08733446e72b983fed850fc5d8bd21b386feb29 inotify: race use after free/double free in inotify inode marks There is a race in the inotify add/rm watch code. A task can find and remove a mark which doesn't have all of it's references. This can result in a use after free/double free situation. Task A Task B ------------ ----------- inotify_new_watch() allocate a mark (refcnt == 1) add it to the idr inotify_rm_watch() inotify_remove_from_idr() fsnotify_put_mark() refcnt hits 0, free take reference because we are on idr [at this point it is a use after free] [time goes on] refcnt may hit 0 again, double free The fix is to take the reference BEFORE the object can be found in the idr. Signed-off-by: Eric Paris Cc: --- diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c index 40da732eb73c..e46ca685b9be 100644 --- a/fs/notify/inotify/inotify_user.c +++ b/fs/notify/inotify/inotify_user.c @@ -546,21 +546,24 @@ retry: if (unlikely(!idr_pre_get(&group->inotify_data.idr, GFP_KERNEL))) goto out_err; + /* we are putting the mark on the idr, take a reference */ + fsnotify_get_mark(&tmp_ientry->fsn_entry); + spin_lock(&group->inotify_data.idr_lock); ret = idr_get_new_above(&group->inotify_data.idr, &tmp_ientry->fsn_entry, group->inotify_data.last_wd+1, &tmp_ientry->wd); spin_unlock(&group->inotify_data.idr_lock); if (ret) { + /* we didn't get on the idr, drop the idr reference */ + fsnotify_put_mark(&tmp_ientry->fsn_entry); + /* idr was out of memory allocate and try again */ if (ret == -EAGAIN) goto retry; goto out_err; } - /* we put the mark on the idr, take a reference */ - fsnotify_get_mark(&tmp_ientry->fsn_entry); - /* we are on the idr, now get on the inode */ ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode); if (ret) {