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Subject[PATCH 3.16 141/157] floppy: fix out-of-bounds read in copy_buffer
3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Denis Efremov <efremov@ispras.ru>

commit da99466ac243f15fbba65bd261bfc75ffa1532b6 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/block/floppy.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3236,8 +3236,10 @@ static int set_geometry(unsigned int cmd
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) ||
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