From 528da3e9e237059a84a2625e942811cf824a6efd Mon Sep 17 00:00:00 2001 From: Eric Paris Date: Fri, 12 Jun 2009 16:04:26 -0400 Subject: [PATCH] inotify: inotify_destroy_mark_entry could get called twice inotify_destroy_mark_entry could get called twice for the same mark since it is called directly in inotify_rm_watch and when the mark is being destroyed for another reason. As an example assume that the file being watched was just deleted so inotify_destroy_mark_entry would get called from the path fsnotify_inoderemove() -> fsnotify_destroy_marks_by_inode() -> fsnotify_destroy_mark_entry() -> inotify_destroy_mark_entry(). If this happened at the same time as userspace tried to remove a watch via inotify_rm_watch we could attempt to remove the mark from the idr twice and could thus double dec the ref cnt and potentially could be in a use after free/double free situation. The fix is to have inotify_rm_watch use the generic recursive safe fsnotify_destroy_mark_by_entry() so we are sure the inotify_destroy_mark_entry() function can only be called one. This patch also renames the function to inotify_ingored_remove_idr() so it is clear what is actually going on in the function. Hopefully this fixes: [ 20.342058] idr_remove called for id=20 which is not allocated. [ 20.348000] Pid: 1860, comm: udevd Not tainted 2.6.30-tip #1077 [ 20.353933] Call Trace: [ 20.356410] [] idr_remove+0x115/0x18f [ 20.361737] [] ? _spin_lock+0x6d/0x75 [ 20.367061] [] ? inotify_destroy_mark_entry+0xa3/0xcf [ 20.373771] [] inotify_destroy_mark_entry+0xb7/0xcf [ 20.380306] [] inotify_freeing_mark+0xe/0x10 [ 20.386238] [] fsnotify_destroy_mark_by_entry+0x143/0x170 [ 20.393293] [] inotify_destroy_mark_entry+0x3c/0xcf [ 20.399829] [] sys_inotify_rm_watch+0x9b/0xc6 [ 20.405850] [] system_call_fastpath+0x16/0x1b Reported-by: Peter Zijlstra Signed-off-by: Eric Paris Tested-by: Peter Ziljlstra --- fs/notify/inotify/inotify.h | 3 ++- fs/notify/inotify/inotify_fsnotify.c | 2 +- fs/notify/inotify/inotify_user.c | 32 +++++--------------------------- 3 files changed, 8 insertions(+), 29 deletions(-) diff --git a/fs/notify/inotify/inotify.h b/fs/notify/inotify/inotify.h index ea2605a58b8a..f234f3a4c8ca 100644 --- a/fs/notify/inotify/inotify.h +++ b/fs/notify/inotify/inotify.h @@ -15,7 +15,8 @@ struct inotify_inode_mark_entry { int wd; }; -extern void inotify_destroy_mark_entry(struct fsnotify_mark_entry *entry, struct fsnotify_group *group); +extern void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry, + struct fsnotify_group *group); extern void inotify_free_event_priv(struct fsnotify_event_private_data *event_priv); extern const struct fsnotify_ops inotify_fsnotify_ops; diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c index 7ef75b83247e..47cd258fd24d 100644 --- a/fs/notify/inotify/inotify_fsnotify.c +++ b/fs/notify/inotify/inotify_fsnotify.c @@ -81,7 +81,7 @@ static int inotify_handle_event(struct fsnotify_group *group, struct fsnotify_ev static void inotify_freeing_mark(struct fsnotify_mark_entry *entry, struct fsnotify_group *group) { - inotify_destroy_mark_entry(entry, group); + inotify_ignored_and_remove_idr(entry, group); } static bool inotify_should_send_event(struct fsnotify_group *group, struct inode *inode, __u32 mask) diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c index 982a412ac5bc..ff231ad23895 100644 --- a/fs/notify/inotify/inotify_user.c +++ b/fs/notify/inotify/inotify_user.c @@ -363,39 +363,17 @@ static int inotify_find_inode(const char __user *dirname, struct path *path, uns } /* - * When, for whatever reason, inotify is done with a mark (or what used to be a - * watch) we need to remove that watch from the idr and we need to send IN_IGNORED - * for the given wd. - * - * There is a bit of recursion here. The loop looks like: - * inotify_destroy_mark_entry -> fsnotify_destroy_mark_by_entry -> - * inotify_freeing_mark -> inotify_destory_mark_entry -> restart - * But the loop is broken in 2 places. fsnotify_destroy_mark_by_entry sets - * entry->group = NULL before the call to inotify_freeing_mark, so the if (egroup) - * test below will not call back to fsnotify again. But even if that test wasn't - * there this would still be safe since fsnotify_destroy_mark_by_entry() is - * safe from recursion. + * Send IN_IGNORED for this wd, remove this wd from the idr, and drop the + * internal reference help on the mark because it is in the idr. */ -void inotify_destroy_mark_entry(struct fsnotify_mark_entry *entry, struct fsnotify_group *group) +void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry, + struct fsnotify_group *group) { struct inotify_inode_mark_entry *ientry; struct inotify_event_private_data *event_priv; struct fsnotify_event_private_data *fsn_event_priv; - struct fsnotify_group *egroup; struct idr *idr; - spin_lock(&entry->lock); - egroup = entry->group; - - /* if egroup we aren't really done and something might still send events - * for this inode, on the callback we'll send the IN_IGNORED */ - if (egroup) { - spin_unlock(&entry->lock); - fsnotify_destroy_mark_by_entry(entry); - return; - } - spin_unlock(&entry->lock); - ientry = container_of(entry, struct inotify_inode_mark_entry, fsn_entry); event_priv = kmem_cache_alloc(event_priv_cachep, GFP_KERNEL); @@ -699,7 +677,7 @@ SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd) fsnotify_get_mark(entry); spin_unlock(&group->inotify_data.idr_lock); - inotify_destroy_mark_entry(entry, group); + fsnotify_destroy_mark_by_entry(entry); fsnotify_put_mark(entry); out: -- 2.11.0