From: Daniel Borkmann <daniel@iogearbox.net>
To: Xu Yu <xuyu@linux.alibaba.com>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] bpf: do not restore dst_reg when cur_state is freed
Date: Thu, 21 Mar 2019 09:50:03 +0100 [thread overview]
Message-ID: <fe7367c5-b172-709f-1ba2-61136a74081e@iogearbox.net> (raw)
In-Reply-To: <eec7905a71d207f7612e9d86e1bf59c43efc65a4.1553156792.git.xuyu@linux.alibaba.com>
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
next prev parent reply other threads:[~2019-03-21 8:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 8:31 [PATCH] bpf: do not restore dst_reg when cur_state is freed Xu Yu
2019-03-21 8:50 ` Daniel Borkmann [this message]
2019-03-21 9:28 ` Yu Xu
2019-03-21 10:00 ` [PATCH v2] " Xu Yu
2019-03-21 11:21 ` Daniel Borkmann
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