bpf: do not restore dst_reg when cur_state is freed
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Message ID eec7905a71d207f7612e9d86e1bf59c43efc65a4.1553156792.git.xuyu@linux.alibaba.com
State Changes Requested
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Series
  • bpf: do not restore dst_reg when cur_state is freed
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Commit Message

Yu Xu March 21, 2019, 8:31 a.m. UTC
Syzkaller hit 'KASAN: use-after-free Write in sanitize_ptr_alu' bug.
Call trace:
  dump_stack+0xbf/0x12e
  print_address_description+0x6a/0x280
  kasan_report+0x237/0x360
  sanitize_ptr_alu+0x85a/0x8d0
  adjust_ptr_min_max_vals+0x8f2/0x1ca0
  adjust_reg_min_max_vals+0x8ed/0x22e0
  do_check+0x1ca6/0x5d00
  bpf_check+0x9ca/0x2570
  bpf_prog_load+0xc91/0x1030
  __se_sys_bpf+0x61e/0x1f00
  do_syscall_64+0xc8/0x550
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
Fault injection trace:
  kfree+0xea/0x290
  free_func_state+0x4a/0x60
  free_verifier_state+0x61/0xe0
  push_stack+0x216/0x2f0	          <- inject failslab
  sanitize_ptr_alu+0x2b1/0x8d0
  adjust_ptr_min_max_vals+0x8f2/0x1ca0
  adjust_reg_min_max_vals+0x8ed/0x22e0
  do_check+0x1ca6/0x5d00
  bpf_check+0x9ca/0x2570
  bpf_prog_load+0xc91/0x1030
  __se_sys_bpf+0x61e/0x1f00
  do_syscall_64+0xc8/0x550
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

When kzalloc() fails in push_stack(), free_verifier_state() will free
current verifier state. As push_stack() returns, dst_reg was restored
if ptr_is_dst_reg is false. However, as member of the cur_state, dst_reg
is also freed, and error occurs when dereferencing dst_reg.

Simply fix it by checking whether cur_state is NULL before retoring
dst_reg.

Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Daniel Borkmann March 21, 2019, 8:50 a.m. UTC | #1
On 03/21/2019 09:31 AM, Xu Yu wrote:
> Syzkaller hit 'KASAN: use-after-free Write in sanitize_ptr_alu' bug.
> Call trace:
>   dump_stack+0xbf/0x12e
>   print_address_description+0x6a/0x280
>   kasan_report+0x237/0x360
>   sanitize_ptr_alu+0x85a/0x8d0
>   adjust_ptr_min_max_vals+0x8f2/0x1ca0
>   adjust_reg_min_max_vals+0x8ed/0x22e0
>   do_check+0x1ca6/0x5d00
>   bpf_check+0x9ca/0x2570
>   bpf_prog_load+0xc91/0x1030
>   __se_sys_bpf+0x61e/0x1f00
>   do_syscall_64+0xc8/0x550
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> Fault injection trace:
>   kfree+0xea/0x290
>   free_func_state+0x4a/0x60
>   free_verifier_state+0x61/0xe0
>   push_stack+0x216/0x2f0	          <- inject failslab
>   sanitize_ptr_alu+0x2b1/0x8d0
>   adjust_ptr_min_max_vals+0x8f2/0x1ca0
>   adjust_reg_min_max_vals+0x8ed/0x22e0
>   do_check+0x1ca6/0x5d00
>   bpf_check+0x9ca/0x2570
>   bpf_prog_load+0xc91/0x1030
>   __se_sys_bpf+0x61e/0x1f00
>   do_syscall_64+0xc8/0x550
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> When kzalloc() fails in push_stack(), free_verifier_state() will free
> current verifier state. As push_stack() returns, dst_reg was restored
> if ptr_is_dst_reg is false. However, as member of the cur_state, dst_reg
> is also freed, and error occurs when dereferencing dst_reg.
> 
> Simply fix it by checking whether cur_state is NULL before retoring
> dst_reg.
> 
> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
> ---
>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index ce166a0..018ce4f 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3368,7 +3368,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
>  		*dst_reg = *ptr_reg;
>  	}
>  	ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true);
> -	if (!ptr_is_dst_reg)
> +	if (!ptr_is_dst_reg && env->cur_state)
>  		*dst_reg = tmp;

Good catch, test should be more obvious rewritten as:

  if (!ptr_is_dst_reg && ret)

Could you resubmit with that?

>  	return !ret ? -EFAULT : 0;
>  }
> 

Thanks,
Daniel
Yu Xu March 21, 2019, 9:28 a.m. UTC | #2
On 3/21/19 4:50 PM, Daniel Borkmann wrote:
> On 03/21/2019 09:31 AM, Xu Yu wrote:
>> Syzkaller hit 'KASAN: use-after-free Write in sanitize_ptr_alu' bug.
>> Call trace:
>>    dump_stack+0xbf/0x12e
>>    print_address_description+0x6a/0x280
>>    kasan_report+0x237/0x360
>>    sanitize_ptr_alu+0x85a/0x8d0
>>    adjust_ptr_min_max_vals+0x8f2/0x1ca0
>>    adjust_reg_min_max_vals+0x8ed/0x22e0
>>    do_check+0x1ca6/0x5d00
>>    bpf_check+0x9ca/0x2570
>>    bpf_prog_load+0xc91/0x1030
>>    __se_sys_bpf+0x61e/0x1f00
>>    do_syscall_64+0xc8/0x550
>>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> Fault injection trace:
>>    kfree+0xea/0x290
>>    free_func_state+0x4a/0x60
>>    free_verifier_state+0x61/0xe0
>>    push_stack+0x216/0x2f0	          <- inject failslab
>>    sanitize_ptr_alu+0x2b1/0x8d0
>>    adjust_ptr_min_max_vals+0x8f2/0x1ca0
>>    adjust_reg_min_max_vals+0x8ed/0x22e0
>>    do_check+0x1ca6/0x5d00
>>    bpf_check+0x9ca/0x2570
>>    bpf_prog_load+0xc91/0x1030
>>    __se_sys_bpf+0x61e/0x1f00
>>    do_syscall_64+0xc8/0x550
>>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> When kzalloc() fails in push_stack(), free_verifier_state() will free
>> current verifier state. As push_stack() returns, dst_reg was restored
>> if ptr_is_dst_reg is false. However, as member of the cur_state, dst_reg
>> is also freed, and error occurs when dereferencing dst_reg.
>>
>> Simply fix it by checking whether cur_state is NULL before retoring
>> dst_reg.
>>
>> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
>> ---
>>   kernel/bpf/verifier.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index ce166a0..018ce4f 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -3368,7 +3368,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
>>   		*dst_reg = *ptr_reg;
>>   	}
>>   	ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true);
>> -	if (!ptr_is_dst_reg)
>> +	if (!ptr_is_dst_reg && env->cur_state)
>>   		*dst_reg = tmp;
> 
> Good catch, test should be more obvious rewritten as:
> 
>    if (!ptr_is_dst_reg && ret)
> 
> Could you resubmit with that?

sure, will send patch v2 later.

thanks,
Yu

> 
>>   	return !ret ? -EFAULT : 0;
>>   }
>>
> 
> Thanks,
> Daniel
>

Patch
diff mbox series

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ce166a0..018ce4f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3368,7 +3368,7 @@  static int sanitize_ptr_alu(struct bpf_verifier_env *env,
 		*dst_reg = *ptr_reg;
 	}
 	ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true);
-	if (!ptr_is_dst_reg)
+	if (!ptr_is_dst_reg && env->cur_state)
 		*dst_reg = tmp;
 	return !ret ? -EFAULT : 0;
 }