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

[Florent Revest]

Acked-by: Florent Revest <revest at chromium.org>

On Tue, Oct 29, 2024 at 7:18 AM Yonghong Song <yonghong.song at linux.dev> wrote:
>
>
> On 10/28/24 12:53 PM, 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>
>
> Acked-by: Yonghong Song <yonghong.song at linux.dev>
>