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floppy: fix out-of-bounds read in copy_buffer

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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>
This commit is contained in:
Denis Efremov 2019-07-12 21:55:23 +03:00 committed by Linus Torvalds
parent 9b04609b78
commit da99466ac2
1 changed files with 4 additions and 2 deletions
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6
drivers/block/floppy.c
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@ -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) ||