Messages in this thread | | | Date | Wed, 16 Sep 2020 16:38:19 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCHv2] perf: Fix race in perf_mmap_close function |
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On Wed, Sep 16, 2020 at 03:54:02PM +0200, peterz@infradead.org wrote: > On Wed, Sep 16, 2020 at 01:53:11PM +0200, Jiri Olsa wrote: > > There's a possible race in perf_mmap_close when checking ring buffer's > > mmap_count refcount value. The problem is that the mmap_count check is > > not atomic because we call atomic_dec and atomic_read separately. > > > > perf_mmap_close: > > ... > > atomic_dec(&rb->mmap_count); > > ... > > if (atomic_read(&rb->mmap_count)) > > goto out_put; > > > > <ring buffer detach> > > free_uid > > > > out_put: > > ring_buffer_put(rb); /* could be last */ > > > > The race can happen when we have two (or more) events sharing same ring > > buffer and they go through atomic_dec and then they both see 0 as refcount > > value later in atomic_read. Then both will go on and execute code which > > is meant to be run just once. > > > > The code that detaches ring buffer is probably fine to be executed more > > than once, but the problem is in calling free_uid, which will later on > > demonstrate in related crashes and refcount warnings, like: > > > > refcount_t: addition on 0; use-after-free. > > ... > > RIP: 0010:refcount_warn_saturate+0x6d/0xf > > ... > > Call Trace: > > prepare_creds+0x190/0x1e0 > > copy_creds+0x35/0x172 > > copy_process+0x471/0x1a80 > > _do_fork+0x83/0x3a0 > > __do_sys_wait4+0x83/0x90 > > __do_sys_clone+0x85/0xa0 > > do_syscall_64+0x5b/0x1e0 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > Using atomic decrease and check instead of separated calls. > > This fixes CVE-2020-14351. > > I'm tempted to remove that line; I can never seem to find anything > useful in a CVE.
I was asked by security guys to add this, Wade?
> > Fixes: ?
right, sry..
Fixes: 9bb5d40cd93c ("perf: Fix mmap() accounting hole");
thanks, jirka
> > > Acked-by: Namhyung Kim <namhyung@kernel.org> > > Tested-by: Michael Petlan <mpetlan@redhat.com> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> >
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