netdev - Re: [PATCH net] bpf: Fix memory leaks in __check_func

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Date:   Fri, 28 Oct 2022 09:36:19 +0800
From:   wangyufen <wangyufen@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, <john.fastabend@...il.com>,
        <andrii@...nel.org>, <martin.lau@...ux.dev>, <yhs@...com>,
        <joe@...d.net.nz>
Subject: Re: [PATCH net] bpf: Fix memory leaks in __check_func_call


在 2022/10/28 4:34, Andrii Nakryiko 写道:
> On Thu, Oct 27, 2022 at 3:03 AM Wang Yufen <wangyufen@...wei.com> wrote:
>> kmemleak reports this issue:
>>
>> unreferenced object 0xffff88817139d000 (size 2048):
>>    comm "test_progs", pid 33246, jiffies 4307381979 (age 45851.820s)
>>    hex dump (first 32 bytes):
>>      01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>    backtrace:
>>      [<0000000045f075f0>] kmalloc_trace+0x27/0xa0
>>      [<0000000098b7c90a>] __check_func_call+0x316/0x1230
>>      [<00000000b4c3c403>] check_helper_call+0x172e/0x4700
>>      [<00000000aa3875b7>] do_check+0x21d8/0x45e0
>>      [<000000001147357b>] do_check_common+0x767/0xaf0
>>      [<00000000b5a595b4>] bpf_check+0x43e3/0x5bc0
>>      [<0000000011e391b1>] bpf_prog_load+0xf26/0x1940
>>      [<0000000007f765c0>] __sys_bpf+0xd2c/0x3650
>>      [<00000000839815d6>] __x64_sys_bpf+0x75/0xc0
>>      [<00000000946ee250>] do_syscall_64+0x3b/0x90
>>      [<0000000000506b7f>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> The root case here is: In function prepare_func_exit(), the callee is
>> not released in the abnormal scenario after "state->curframe--;".
>>
>> In addition, function __check_func_call() has a similar problem. In
>> the abnormal scenario before "state->curframe++;", the callee is alse
>> not released.
> For prepare_func_exit, wouldn't it be correct and cleaner to just move
> state->curframe--; to the very bottom of the function, right when we
> free callee and reset frame[] pointer to NULL?

Yes, that't better. will change and test in v2.

> For __check_func_call, please use err_out label name to disambiguate
> it from the "err" variable.

I got it. will change in v2.

>
>> Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
>> Fixes: fd978bf7fd31 ("bpf: Add reference tracking to verifier")
>> Signed-off-by: Wang Yufen <wangyufen@...wei.com>
>> ---
>>   kernel/bpf/verifier.c | 25 ++++++++++++++++---------
>>   1 file changed, 16 insertions(+), 9 deletions(-)
>>
> [...]