[lvc-project] [PATCH bpf v2 1/2] bpf: fix %p% runtime check in bpf_bprintf_prepare

[Fedor Pchelkin]

On Mon, 28. Oct 19:53, Ilya Shchipletsov wrote:
> Fuzzing reports a warning in format_decode()
> 
> Please remove unsupported %� in format string
> WARNING: CPU: 0 PID: 5091 at lib/vsprintf.c:2680 format_decode+0x1193/0x1bb0 lib/vsprintf.c:2680
> Modules linked in:
> CPU: 0 PID: 5091 Comm: syz-executor879 Not tainted 6.10.0-rc1-syzkaller-00021-ge0cce98fe279 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
> RIP: 0010:format_decode+0x1193/0x1bb0 lib/vsprintf.c:2680
> Call Trace:
>  <TASK>
>  bstr_printf+0x137/0x1210 lib/vsprintf.c:3253
>  ____bpf_trace_printk kernel/trace/bpf_trace.c:390 [inline]
>  bpf_trace_printk+0x1a1/0x230 kernel/trace/bpf_trace.c:375
>  bpf_prog_21da1b68f62e1237+0x36/0x41
>  bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
>  __bpf_prog_run include/linux/filter.h:691 [inline]
>  bpf_prog_run include/linux/filter.h:698 [inline]
>  bpf_test_run+0x40b/0x910 net/bpf/test_run.c:425
>  bpf_prog_test_run_skb+0xafa/0x13a0 net/bpf/test_run.c:1066
>  bpf_prog_test_run+0x33c/0x3b0 kernel/bpf/syscall.c:4291
>  __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5705
>  __do_sys_bpf kernel/bpf/syscall.c:5794 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5792 [inline]
>  __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5792
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> The problem occurs when trying to pass %p% at the end of format string,
> which would result in skipping last % and passing invalid format string
> down to format_decode() that would cause warning because of invalid
> character after %.
> 
> Fix issue by advancing pointer only if next char is format modifier.
> If next char is null/space/punct, then just accept formatting as is,
> without advancing the pointer.
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Reported-by: syzbot+e2c932aec5c8a6e1d31c at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=e2c932aec5c8a6e1d31c
> Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
> Co-developed-by: Nikita Marushkin <hfggklm at gmail.com>
> Signed-off-by: Nikita Marushkin <hfggklm at gmail.com>
> Signed-off-by: Ilya Shchipletsov <rabbelkin at mail.ru>

Вот сюда после Вашего Signed-off-by и перед --- без пустых строк можете добавить:
Acked-by: Yonghong Song <yonghong.song at linux.dev>
Acked-by: Florent Revest <revest at chromium.org>

Ко второму патчу серии - то же самое.

> ---
>  kernel/bpf/helpers.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 1a43d06eab28..3efa8b04999a 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -889,10 +889,8 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
>  				goto fmt_str;
>  			}
>  
> -			if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) ||
> -			    ispunct(fmt[i + 1]) || fmt[i + 1] == 'K' ||
> -			    fmt[i + 1] == 'x' || fmt[i + 1] == 's' ||
> -			    fmt[i + 1] == 'S') {
> +			if (fmt[i + 1] == 'K' || fmt[i + 1] == 'x' ||
> +			    fmt[i + 1] == 's' || fmt[i + 1] == 'S') {
>  				/* just kernel pointers */
>  				if (tmp_buf)
>  					cur_arg = raw_args[num_spec];
> @@ -900,6 +898,13 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
>  				goto nocopy_fmt;
>  			}
>  
> +			if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) ||
> +			    ispunct(fmt[i + 1])) {
> +				if (tmp_buf)
> +					cur_arg = raw_args[num_spec];
> +				goto nocopy_fmt;
> +			}
> +
>  			if (fmt[i + 1] == 'B') {
>  				if (tmp_buf)  {
>  					err = snprintf(tmp_buf,
> -- 
> 2.43.0
> 
> 
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