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inotify: inotify_destroy_mark_entry could get called twice

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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]  [<ffffffff811a82b7>] idr_remove+0x115/0x18f
[   20.361737]  [<ffffffff8134259d>] ? _spin_lock+0x6d/0x75
[   20.367061]  [<ffffffff8111640a>] ? inotify_destroy_mark_entry+0xa3/0xcf
[   20.373771]  [<ffffffff8111641e>] inotify_destroy_mark_entry+0xb7/0xcf
[   20.380306]  [<ffffffff81115913>] inotify_freeing_mark+0xe/0x10
[   20.386238]  [<ffffffff8111410d>] fsnotify_destroy_mark_by_entry+0x143/0x170
[   20.393293]  [<ffffffff811163a3>] inotify_destroy_mark_entry+0x3c/0xcf
[   20.399829]  [<ffffffff811164d1>] sys_inotify_rm_watch+0x9b/0xc6
[   20.405850]  [<ffffffff8100bcdb>] system_call_fastpath+0x16/0x1b

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Eric Paris <eparis@redhat.com>
Tested-by: Peter Ziljlstra <peterz@infradead.org>
This commit is contained in:
Eric Paris 2009-06-12 16:04:26 -04:00
parent 0732f87761
commit 528da3e9e2
3 changed files with 8 additions and 29 deletions
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3
fs/notify/inotify/inotify.h
View File

@ -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;

2
fs/notify/inotify/inotify_fsnotify.c
View File

@ -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)

32
fs/notify/inotify/inotify_user.c
View File

@ -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: