lkml.org 
[lkml]   [2019]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] bpf: do not restore dst_reg when cur_state is freed
From
Date
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

\
 
 \ /
  Last update: 2019-03-21 09:50    [W:0.057 / U:0.016 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site