floppy: fix out-of-bounds read in copy_buffer

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

The FDDEFPRM ioctl allows one to set the geometry of a disk.  The sect
and head fields (unsigned int) of the floppy_drive structure are used to
compute the max_sector (int) in the make_raw_rw_request function.  It is
possible to overflow the max_sector.  Next, max_sector is passed to the
copy_buffer function and used in one of the memcpy calls.

An unprivileged user could trigger the bug if the device is accessible,
but requires a floppy disk to be inserted.

The patch adds the check for the .sect * .head multiplication for not
overflowing in the set_geometry function.

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, 4 insertions, 2 deletions

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 671a0ae434b4..fee57f7f3821 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3233,8 +3233,10 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
         int cnt;
 
         /* sanity checking for parameters. */
-        if (g->sect <= 0 ||
-            g->head <= 0 ||
+        if ((int)g->sect <= 0 ||
+            (int)g->head <= 0 ||
+            /* check for overflow in max_sector */
+            (int)(g->sect * 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) ||