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SubjectRe: [PATCH v2] bpf: do not restore dst_reg when cur_state is freed
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On 03/21/2019 11:00 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 testing ret of push_stack() before retoring dst_reg.
>
> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>

Applied, thanks!

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