floppy: fix out-of-bounds read in next_valid_format

This fixes a global out-of-bounds read access in the next_valid_format
function of the floppy driver.

The values from autodetect field of the struct floppy_drive_params are
used as indices for the floppy_type array in the next_valid_format
function 'floppy_type[DP->autodetect[probed_format]].sect'.

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

CAP_SYS_ADMIN is required to call FDSETDRVPRM.

The patch adds the check for values of the autodetect 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>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 51246bc9709a..b70d6e103a57 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3380,6 +3380,20 @@ static int fd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
         return 0;
 }
 
+static bool valid_floppy_drive_params(const short autodetect[8])
+{
+        size_t floppy_type_size = ARRAY_SIZE(floppy_type);
+        size_t i = 0;
+
+        for (i = 0; i < 8; ++i) {
+                if (autodetect[i] < 0 ||
+                    autodetect[i] >= floppy_type_size)
+                        return false;
+        }
+
+        return true;
+}
+
 static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd,
                     unsigned long param)
 {
@@ -3506,6 +3520,8 @@ 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))
+                        return -EINVAL;
                 *UDP = inparam.dp;
                 break;
         case FDGETDRVPRM:
@@ -3703,6 +3719,8 @@ static int compat_setdrvprm(int drive,
                 return -EPERM;
         if (copy_from_user(&v, arg, sizeof(struct compat_floppy_drive_params)))
                 return -EFAULT;
+        if (!valid_floppy_drive_params(v.autodetect))
+                return -EINVAL;
         mutex_lock(&floppy_mutex);
         UDP->cmos = v.cmos;
         UDP->max_dtr = v.max_dtr;