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