Forwarded: [PATCH] blktrace: reject buf_size smaller than struct blk_io_trace

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@xxxxxxxxxxxxxxx, syzkaller-bugs@xxxxxxxxxxxxxxxx.

***

Subject: [PATCH] blktrace: reject buf_size smaller than struct blk_io_trace
Author: kartikey406@xxxxxxxxx

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


blk_trace_setup() accepts any non-zero buf_size from userspace
and passes it directly to relay_open(). If buf_size is smaller
than sizeof(struct blk_io_trace) = 40 bytes, relay_switch_subbuf()
always hits the toobig path and returns 0, causing memory pressure
that leads to bio_alloc() failing under GFP_NOIO and a
null-ptr-deref in bio_add_folio().

Reject buf_size values too small to hold a single trace event.

Reported-by: syzbot+ed8bc247f231c1a48e21@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=ed8bc247f231c1a48e21
Signed-off-by: Deepanshu Kartikey <Kartikey406@xxxxxxxxx>
---
 kernel/trace/blktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 8cd2520b4c99..6cc7d83ed1c2 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -773,7 +773,7 @@ int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	if (ret)
 		return -EFAULT;
 
-	if (!buts.buf_size || !buts.buf_nr)
+	if (buts.buf_size < sizeof(struct blk_io_trace) || !buts.buf_nr)
 		return -EINVAL;
 
 	buts2 = (struct blk_user_trace_setup2) {
-- 
2.43.0