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Message-Id: <20190724191708.899798884@linuxfoundation.org>
Date: Wed, 24 Jul 2019 21:20:29 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Denis Efremov <efremov@...ras.ru>,
Willy Tarreau <w@....eu>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 160/271] floppy: fix div-by-zero in setup_format_params
[ Upstream commit f3554aeb991214cbfafd17d55e2bfddb50282e32 ]
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@...ras.ru>
Tested-by: Willy Tarreau <w@....eu>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
drivers/block/floppy.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index a8de56f1936d..b1425b218606 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2119,6 +2119,9 @@ 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;
@@ -3243,6 +3246,8 @@ 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)
--
2.20.1
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