Messages in this thread | | | Subject | Re: [bpf-next 3/3] bpf: Fix a use after free in bpf_check() | From | He Fengqing <> | Date | Fri, 9 Jul 2021 19:11:25 +0800 |
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在 2021/7/8 11:09, Alexei Starovoitov 写道: > On Wed, Jul 7, 2021 at 8:00 PM He Fengqing <hefengqing@huawei.com> wrote: >> >> Ok, I will change this in next version. > > before you spam the list with the next version > please explain why any of these changes are needed? > I don't see an explanation in the patches and I don't see a bug in the code. > Did you check what is the prog clone ? > When is it constructed? Why verifier has anything to do with it? > . >
I'm sorry, I didn't describe these errors clearly.
bpf_check(bpf_verifier_env) | |->do_misc_fixups(env) | | | |->bpf_patch_insn_data(env) | | | | | |->bpf_patch_insn_single(env->prog) | | | | | | | |->bpf_prog_realloc(env->prog) | | | | | | | | | |->construct new_prog | | | | | free old_prog(env->prog) | | | | | | | | | |->return new_prog; | | | | | | | |->return new_prog; | | | | | |->adjust_insn_aux_data | | | | | | | |->return ENOMEM; | | | | | |->return NULL; | | | |->return ENOMEM;
bpf_verifier_env->prog had been freed in bpf_prog_realloc function.
There are two errors here, the first is memleak in the bpf_patch_insn_data function, and the second is use after free in the bpf_check function.
memleak in bpf_patch_insn_data:
Look at the call chain above, if adjust_insn_aux_data function return ENOMEM, bpf_patch_insn_data will return NULL, but we do not free the new_prog.
So in the patch 2, before bpf_patch_insn_data return NULL, we free the new_prog.
use after free in bpf_check:
If bpf_patch_insn_data function return NULL, we will not assign new_prog to the bpf_verifier_env->prog, but bpf_verifier_env->prog has been freed in the bpf_prog_realloc function. Then in bpf_check function, we will use bpf_verifier_env->prog after do_misc_fixups function.
In the patch 3, I added a free_old parameter to bpf_prog_realloc, in this scenario we don't free old_prog. Instead, we free it in the do_misc_fixups function when bpf_patch_insn_data return a valid new_prog.
Thanks for your reviews.
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