在 2021/7/8 11:09, Alexei Starovoitov 写道:
On Wed, Jul 7, 2021 at 8:00 PM He Fengqing <hefengqing@xxxxxxxxxx> 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.
