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

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Date:   Thu, 27 Oct 2022 13:34:47 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Wang Yufen <wangyufen@...wei.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

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?

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

>
> 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(-)
>

[...]