linux-kernel - [PATCH] tracing: fix oob write in trace_seq_to

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Message-ID: <20250421134936.89104-1-aha310510@gmail.com>
Date: Mon, 21 Apr 2025 22:49:36 +0900
From: Jeongjun Park <aha310510@...il.com>
To: rostedt@...dmis.org,
	mhiramat@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	syzbot+c8cd2d2c412b868263fb@...kaller.appspotmail.com,
	Jeongjun Park <aha310510@...il.com>
Subject: [PATCH] tracing: fix oob write in trace_seq_to_buffer()

syzbot reported this bug:
==================================================================
BUG: KASAN: slab-out-of-bounds in trace_seq_to_buffer kernel/trace/trace.c:1830 [inline]
BUG: KASAN: slab-out-of-bounds in tracing_splice_read_pipe+0x6be/0xdd0 kernel/trace/trace.c:6822
Write of size 4507 at addr ffff888032b6b000 by task syz.2.320/7260

CPU: 1 UID: 0 PID: 7260 Comm: syz.2.320 Not tainted 6.15.0-rc1-syzkaller-00301-g3bde70a2c827 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xc3/0x670 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
 __asan_memcpy+0x3c/0x60 mm/kasan/shadow.c:106
 trace_seq_to_buffer kernel/trace/trace.c:1830 [inline]
 tracing_splice_read_pipe+0x6be/0xdd0 kernel/trace/trace.c:6822
 ....
==================================================================

It has been reported that trace_seq_to_buffer() attempts to copy more than
PAGE_SIZE data into buf, so we need to add code to check the size of the 
cnt value to prevent this.

Reported-by: syzbot+c8cd2d2c412b868263fb@...kaller.appspotmail.com
Fixes: 3c56819b14b0 ("tracing: splice support for tracing_pipe")
Signed-off-by: Jeongjun Park <aha310510@...il.com>
---
 kernel/trace/trace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8ddf6b17215c..8ba6ea38411d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1827,6 +1827,8 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
 	len = trace_seq_used(s) - s->readpos;
 	if (cnt > len)
 		cnt = len;
+	if (cnt > PAGE_SIZE)
+		return -EINVAL;
 	memcpy(buf, s->buffer + s->readpos, cnt);

 	s->readpos += cnt;
--