Messages in this thread | | | Subject | Re: [PATCH] bpf: do not restore dst_reg when cur_state is freed | From | Yu Xu <> | Date | Thu, 21 Mar 2019 17:28:41 +0800 |
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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 >
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