From: Denis Efremov <efremov@ispras.ru>
Date: Fri, 12 Jul 2019 18:55:22 +0000 (+0300)
Subject: floppy: fix invalid pointer dereference in drive_name
X-Git-Tag: v3.16.72~18
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fbf6a95d0a3d410ee2f4530e243b77beee87c76a;p=thirdparty%2Fkernel%2Fstable.git

floppy: fix invalid pointer dereference in drive_name

commit 9b04609b784027968348796a18f601aed9db3789 upstream.

This fixes the invalid pointer dereference in the drive_name function of
the floppy driver.

The native_format field of the struct floppy_drive_params is used as
floppy_type array index in the drive_name function.  Thus, the field
should be checked the same way as the autodetect field.

To trigger the bug, one could use a value out of range and set the drive
parameters with the FDSETDRVPRM ioctl.  Next, FDGETDRVTYP ioctl should
be used to call the drive_name.  A floppy disk is not required to be
inserted.

CAP_SYS_ADMIN is required to call FDSETDRVPRM.

The patch adds the check for a value of the native_format field to be in
the '0 <= x < ARRAY_SIZE(floppy_type)' range of the floppy_type array
indices.

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>
[bwh: Backported to 3.16: Drop changes in compat_setdrvprm(), as compat
 ioctls go via fd_ioctl_locked() after translation in compat_ioctl.c.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 7345154fde581..2d6087bb3bc4e 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3383,7 +3383,8 @@ static int fd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
 	return 0;
 }
 
-static bool valid_floppy_drive_params(const short autodetect[8])
+static bool valid_floppy_drive_params(const short autodetect[8],
+		int native_format)
 {
 	size_t floppy_type_size = ARRAY_SIZE(floppy_type);
 	size_t i = 0;
@@ -3394,6 +3395,9 @@ static bool valid_floppy_drive_params(const short autodetect[8])
 			return false;
 	}
 
+	if (native_format < 0 || native_format >= floppy_type_size)
+		return false;
+
 	return true;
 }
 
@@ -3523,7 +3527,8 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 		SUPBOUND(size, strlen((const char *)outparam) + 1);
 		break;
 	case FDSETDRVPRM:
-		if (!valid_floppy_drive_params(inparam.dp.autodetect))
+		if (!valid_floppy_drive_params(inparam.dp.autodetect,
+				inparam.dp.native_format))
 			return -EINVAL;
 		*UDP = inparam.dp;
 		break;