[PATCH 3.16 140/157] floppy: fix invalid pointer dereference in drive_name

[Ben Hutchings]

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Denis Efremov <efremov@xxxxxxxxx>

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@xxxxxxxxx>
Tested-by: Willy Tarreau <w@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[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@xxxxxxxxxxxxxxx>
---
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3383,7 +3383,8 @@ static int fd_getgeo(struct block_device
 	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(co
 			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_
 		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;