From f3554aeb991214cbfafd17d55e2bfddb50282e32 Mon Sep 17 00:00:00 2001
From: Denis Efremov <efremov@ispras.ru>
Date: Fri, 12 Jul 2019 21:55:20 +0300
Subject: [PATCH] floppy: fix div-by-zero in setup_format_params
Git-commit: f3554aeb991214cbfafd17d55e2bfddb50282e32
Patch-mainline: v5.3-rc1
References: CVE-2019-14284,bsc#1143189
This fixes a divide by zero error in the setup_format_params function of
the floppy driver.
Two consecutive ioctls can trigger the bug: The first one should set the
drive geometry with such .sect and .rate values for the F_SECT_PER_TRACK
to become zero. Next, the floppy format operation should be called.
A floppy disk is not required to be inserted. An unprivileged user
could trigger the bug if the device is accessible.
The patch checks F_SECT_PER_TRACK for a non-zero value in the
set_geometry function. The proper check should involve a reasonable
upper limit for the .sect and .rate fields, but it could change the
UAPI.
The patch also checks F_SECT_PER_TRACK in the setup_format_params, and
cancels the formatting operation in case of zero.
The bug was found by syzkaller.
Signed-off-by: Denis Efremov <efremov@ispras.ru>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/block/floppy.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 9fb9b312ab6b..51246bc9709a 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2120,6 +2120,9 @@ static void setup_format_params(int track)
raw_cmd->kernel_data = floppy_track_buffer;
raw_cmd->length = 4 * F_SECT_PER_TRACK;
+ if (!F_SECT_PER_TRACK)
+ return;
+
/* allow for about 30ms for data transport per track */
head_shift = (F_SECT_PER_TRACK + 5) / 6;
@@ -3232,6 +3235,8 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
/* sanity checking for parameters. */
if (g->sect <= 0 ||
g->head <= 0 ||
+ /* check for zero in F_SECT_PER_TRACK */
+ (unsigned char)((g->sect << 2) >> FD_SIZECODE(g)) == 0 ||
g->track <= 0 || g->track > UDP->tracks >> STRETCH(g) ||
/* check if reserved bits are set */
(g->stretch & ~(FD_STRETCH | FD_SWAPSIDES | FD_SECTBASEMASK)) != 0)
--
2.16.4