* [PATCH] bpf: fix check of allowed specifiers in bpf_trace_printk
@ 2018-11-22 16:00 Martynas Pumputis
2018-11-22 21:31 ` Daniel Borkmann
0 siblings, 1 reply; 2+ messages in thread
From: Martynas Pumputis @ 2018-11-22 16:00 UTC (permalink / raw)
To: netdev; +Cc: ast, daniel, m
A format string consisting of "%p" or "%s" followed by an invalid
specifier (e.g. "%p%\n" or "%s%") could pass the check which
would make format_decode (lib/vsprintf.c) to warn.
Reported-by: syzbot+1ec5c5ec949c4adaa0c4@syzkaller.appspotmail.com
Signed-off-by: Martynas Pumputis <m@lambda.lt>
---
kernel/trace/bpf_trace.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 08fcfe440c63..9ab05736e1a1 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -225,6 +225,8 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
(void *) (long) unsafe_addr,
sizeof(buf));
}
+ if (fmt[i] == '%')
+ i--;
continue;
}
--
2.19.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] bpf: fix check of allowed specifiers in bpf_trace_printk
2018-11-22 16:00 [PATCH] bpf: fix check of allowed specifiers in bpf_trace_printk Martynas Pumputis
@ 2018-11-22 21:31 ` Daniel Borkmann
0 siblings, 0 replies; 2+ messages in thread
From: Daniel Borkmann @ 2018-11-22 21:31 UTC (permalink / raw)
To: Martynas Pumputis, netdev; +Cc: ast
Hi Martynas,
On 11/22/2018 05:00 PM, Martynas Pumputis wrote:
> A format string consisting of "%p" or "%s" followed by an invalid
> specifier (e.g. "%p%\n" or "%s%") could pass the check which
> would make format_decode (lib/vsprintf.c) to warn.
>
> Reported-by: syzbot+1ec5c5ec949c4adaa0c4@syzkaller.appspotmail.com
> Signed-off-by: Martynas Pumputis <m@lambda.lt>
> ---
> kernel/trace/bpf_trace.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 08fcfe440c63..9ab05736e1a1 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -225,6 +225,8 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
> (void *) (long) unsafe_addr,
> sizeof(buf));
> }
> + if (fmt[i] == '%')
> + i--;
> continue;
> }
Thanks for the fix! Could we simplify the logic a bit to avoid having to
navigate i back and forth which got us in trouble in the first place? Like
below (untested) perhaps?
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 08fcfe4..ff83b8c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -196,11 +196,13 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
i++;
} else if (fmt[i] == 'p' || fmt[i] == 's') {
mod[fmt_cnt]++;
- i++;
- if (!isspace(fmt[i]) && !ispunct(fmt[i]) && fmt[i] != 0)
+ /* Disallow any further format extensions. */
+ if (fmt[i + 1] != 0 &&
+ !isspace(fmt[i + 1]) &&
+ !ispunct(fmt[i + 1]))
return -EINVAL;
fmt_cnt++;
- if (fmt[i - 1] == 's') {
+ if (fmt[i] == 's') {
if (str_seen)
/* allow only one '%s' per fmt string */
return -EINVAL;
Thanks,
Daniel
^ permalink raw reply related [flat|nested] 2+ messages in thread
end of thread, other threads:[~2018-11-23 8:12 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-22 16:00 [PATCH] bpf: fix check of allowed specifiers in bpf_trace_printk Martynas Pumputis
2018-11-22 21:31 ` Daniel Borkmann
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.