This is a note to let you know that I've just added the patch titled

hpet: Fix division by zero in hpet_time_div()

to my char-misc git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 0c7d37f4d9b8446956e97b7c5e61173cdb7c8522 Mon Sep 17 00:00:00 2001

From: Kefeng Wang wangkefeng.wang@huawei.com Date: Thu, 11 Jul 2019 21:27:57 +0800 Subject: hpet: Fix division by zero in hpet_time_div()

The base value in do_div() called by hpet_time_div() is truncated from unsigned long to uint32_t, resulting in a divide-by-zero exception.

UBSAN: Undefined behaviour in ../drivers/char/hpet.c:572:2 division by zero CPU: 1 PID: 23682 Comm: syz-executor.3 Not tainted 4.4.184.x86_64+ #4 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 0000000000000000 b573382df1853d00 ffff8800a3287b98 ffffffff81ad7561 ffff8800a3287c00 ffffffff838b35b0 ffffffff838b3860 ffff8800a3287c20 0000000000000000 ffff8800a3287bb0 ffffffff81b8f25e ffffffff838b35a0 Call Trace: [<ffffffff81ad7561>] __dump_stack lib/dump_stack.c:15 [inline] [<ffffffff81ad7561>] dump_stack+0xc1/0x120 lib/dump_stack.c:51 [<ffffffff81b8f25e>] ubsan_epilogue+0x12/0x8d lib/ubsan.c:166 [<ffffffff81b900cb>] __ubsan_handle_divrem_overflow+0x282/0x2c8 lib/ubsan.c:262 [<ffffffff823560dd>] hpet_time_div drivers/char/hpet.c:572 [inline] [<ffffffff823560dd>] hpet_ioctl_common drivers/char/hpet.c:663 [inline] [<ffffffff823560dd>] hpet_ioctl_common.cold+0xa8/0xad drivers/char/hpet.c:577 [<ffffffff81e63d56>] hpet_ioctl+0xc6/0x180 drivers/char/hpet.c:676 [<ffffffff81711590>] vfs_ioctl fs/ioctl.c:43 [inline] [<ffffffff81711590>] file_ioctl fs/ioctl.c:470 [inline] [<ffffffff81711590>] do_vfs_ioctl+0x6e0/0xf70 fs/ioctl.c:605 [<ffffffff81711eb4>] SYSC_ioctl fs/ioctl.c:622 [inline] [<ffffffff81711eb4>] SyS_ioctl+0x94/0xc0 fs/ioctl.c:613 [<ffffffff82846003>] tracesys_phase2+0x90/0x95

The main C reproducer autogenerated by syzkaller,

syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0); memcpy((void*)0x20000100, "/dev/hpet\000", 10); syscall(__NR_openat, 0xffffffffffffff9c, 0x20000100, 0, 0); syscall(__NR_ioctl, r[0], 0x40086806, 0x40000000000000);

Fix it by using div64_ul().

Signed-off-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Zhang HongJun zhanghongjun2@huawei.com Cc: stable stable@vger.kernel.org Reviewed-by: Arnd Bergmann arnd@arndb.de Link: https://lore.kernel.org/r/20190711132757.130092-1-wangkefeng.wang@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/hpet.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c index 5c39f20378b8..9ac6671bb514 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -567,8 +567,7 @@ static inline unsigned long hpet_time_div(struct hpets *hpets, unsigned long long m;

m = hpets->hp_tick_freq + (dis >> 1); - do_div(m, dis); - return (unsigned long)m; + return div64_ul(m, dis); }

static int