[PATCH] floppy: don't store a stack buffer in timeout_message

["Denis Efremov (Oracle)" <efremov@linux.com>]

request_done() formats "request done %d" into a buffer on its stack and
passes it to reschedule_timeout(), which keeps the pointer in
timeout_message. show_floppy() prints timeout_message long after
request_done() has returned, e.g. from result() in the interrupt
handler, and reads a dead stack frame:

  BUG: KASAN: stack-out-of-bounds in string+0x39c/0x3d0 lib/vsprintf.c:720
  Read of size 1 at addr ffffc900003cfc70 by task swapper/3/0
  Call Trace:
   <IRQ>
   ...
   show_floppy+0xb1/0x45f drivers/block/floppy.c:1838
   result.cold+0x2b/0x30 drivers/block/floppy.c:1183
   floppy_interrupt+0x191/0x340 drivers/block/floppy.c:1755
   floppy_hardint+0x1a7/0x200 arch/x86/include/asm/floppy.h:66

uptodate is either 0 or 1, so pass one of two string literals instead.

Cc: stable@vger.kernel.org
Fixes: 73507e6cd8dc ("drivers/block/floppy.c: remove unnecessary argument from [__]reschedule_timeout")
Reported-by: syzbot+874c2707f97fac24b090@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=874c2707f97fac24b090
Signed-off-by: Denis Efremov (Oracle) <efremov@linux.com>
---
 drivers/block/floppy.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index f04397b8e381..02a34de69102 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2276,11 +2276,10 @@ static void request_done(int uptodate)
 {
 	struct request *req = current_req;
 	int block;
-	char msg[sizeof("request done ") + sizeof(int) * 3];
 
 	probing = 0;
-	snprintf(msg, sizeof(msg), "request done %d", uptodate);
-	reschedule_timeout(MAXTIMEOUT, msg);
+	reschedule_timeout(MAXTIMEOUT,
+			   uptodate ? "request done 1" : "request done 0");
 
 	if (!req) {
 		pr_info("floppy.c: no request in request_done\n");

base-commit: 62f4c998b297cf233997a2b4cd6fc2d2df0319c9
-- 
2.55.0