From: Alexei Starovoitov <ast@plumgrid•com>
To: Hannes Frederic Sowa <hannes@stressinduktion•org>
Cc: "David S. Miller" <davem@davemloft•net>,
Daniel Borkmann <daniel@iogearbox•net>,
netdev@vger•kernel.org
Subject: Re: [PATCH net] bpf: fix verifier memory corruption
Date: Wed, 15 Apr 2015 09:07:36 -0700 [thread overview]
Message-ID: <552E8CC8.9070403@plumgrid.com> (raw)
In-Reply-To: <1429113575.12070.19.camel@stressinduktion.org>
On 4/15/15 8:59 AM, Hannes Frederic Sowa wrote:
> On Di, 2015-04-14 at 15:57 -0700, Alexei Starovoitov wrote:
>> Due to missing bounds check the DAG pass of the BPF verifier can corrupt
>> the memory which can cause random crashes during program loading:
>>
>> [8.449451] BUG: unable to handle kernel paging request at ffffffffffffffff
>> [8.451293] IP: [<ffffffff811de33d>] kmem_cache_alloc_trace+0x8d/0x2f0
>> [8.452329] Oops: 0000 [#1] SMP
>> [8.452329] Call Trace:
>> [8.452329] [<ffffffff8116cc82>] bpf_check+0x852/0x2000
>> [8.452329] [<ffffffff8116b7e4>] bpf_prog_load+0x1e4/0x310
>> [8.452329] [<ffffffff811b190f>] ? might_fault+0x5f/0xb0
>> [8.452329] [<ffffffff8116c206>] SyS_bpf+0x806/0xa30
>>
>> Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
>> Signed-off-by: Alexei Starovoitov <ast@plumgrid•com>
>> ---
>> Many things need to align for this crash to be seen, yet I managed to hit it.
>> In my case JA was last insn, 't' was 255 and explored_states array
>> had 256 elements. I've double checked other similar paths and all seems clean.
>>
>> kernel/bpf/verifier.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index a28e09c7825d..36508e69e92a 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -1380,7 +1380,8 @@ peek_stack:
>> /* tell verifier to check for equivalent states
>> * after every call and jump
>> */
>> - env->explored_states[t + 1] = STATE_LIST_MARK;
>> + if (t + 1 < insn_cnt)
>> + env->explored_states[t + 1] = STATE_LIST_MARK;
>> } else {
>> /* conditional jump with two edges */
>> ret = push_insn(t, t + 1, FALLTHROUGH, env);
>
> Quick review:
>
> We have env->explored_states[t+1] access in the
>
> } else {
> /* conditional jump with two edges */
> ret = push_insn(t, t + 1, FALLTHROUGH, env);
> if (ret == 1)
> goto peek_stack;
> else if (ret < 0)
> goto err_free;
>
>>>> ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
> if (ret == 1)
> goto peek_stack;
> else if (ret < 0)
> goto err_free;
> }
> } else {
>
>
> push_insn call. At this point insn[t].off could be 0, no?
insn[t].off can be anything, but the first thing that push_insn()
checks is:
if (w < 0 || w >= env->prog->len)
only then it does:
env->explored_states[w] = STATE_LIST_MARK;
so we're good there.
Though thanks for triple checking :)
next prev parent reply other threads:[~2015-04-15 16:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-14 22:57 [PATCH net] bpf: fix verifier memory corruption Alexei Starovoitov
2015-04-15 15:59 ` Hannes Frederic Sowa
2015-04-15 16:07 ` Alexei Starovoitov [this message]
2015-04-15 16:12 ` Hannes Frederic Sowa
2015-04-15 17:05 ` Daniel Borkmann
2015-04-16 16:07 ` David Miller
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