From: Denis Efremov <efremov@xxxxxxxxx> [ Upstream commit da99466ac243f15fbba65bd261bfc75ffa1532b6 ] 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@xxxxxxxxx> Tested-by: Willy Tarreau <w@xxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/block/floppy.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c index 42ae1d2d8243..7516fed84ae9 100644 --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -3236,8 +3236,10 @@ 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) || -- 2.20.1
