[PATCH net] bpf: fix verifier memory corruption

[PATCH net] bpf: fix verifier memory corruption

[Alexei Starovoitov]

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);
-- 
1.7.9.5

Re: [PATCH net] bpf: fix verifier memory corruption

[Hannes Frederic Sowa]

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?

Thanks,
Hannes

Re: [PATCH net] bpf: fix verifier memory corruption

[Alexei Starovoitov]

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 :)

Re: [PATCH net] bpf: fix verifier memory corruption

[Hannes Frederic Sowa]

On Wed, Apr 15, 2015, at 18:07, Alexei Starovoitov wrote:
> 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 :)

Sorry, yes. That check was too obvious to me. ;)

Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

Bye,
Hannes

Re: [PATCH net] bpf: fix verifier memory corruption

[Daniel Borkmann]

On 04/15/2015 12:57 AM, 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>

As far as I can tell, looks good to me. Any other access to a next
instruction elsewhere would be blocked from push_insn() with an error.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Re: [PATCH net] bpf: fix verifier memory corruption

[David Miller]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Tue, 14 Apr 2015 15:57:13 -0700

> 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>

Applied and queued up for -stable, thanks.