From: Willem de Bruijn <willemb@xxxxxxxxxx>
ppp_sync_ioctl allows setting device MRU, but does not sanity check
this input.
Limit to a sane upper bound of 64KB.
No implementation I could find generates larger than 64KB frames.
RFC 2823 mentions an upper bound of PPP over SDL of 64KB based on the
16-bit length field. Other protocols will be smaller, such as PPPoE
(9KB jumbo frame) and PPPoA (18190 maximum CPCS-SDU size, RFC 2364).
PPTP and L2TP encapsulate in IP.
Syzbot managed to trigger alloc warning in __alloc_pages:
if (WARN_ON_ONCE_GFP(order > MAX_ORDER, gfp))
WARNING: CPU: 1 PID: 37 at mm/page_alloc.c:4544 __alloc_pages+0x3ab/0x4a0 mm/page_alloc.c:4544
__alloc_skb+0x12b/0x330 net/core/skbuff.c:651
__netdev_alloc_skb+0x72/0x3f0 net/core/skbuff.c:715
netdev_alloc_skb include/linux/skbuff.h:3225 [inline]
dev_alloc_skb include/linux/skbuff.h:3238 [inline]
ppp_sync_input drivers/net/ppp/ppp_synctty.c:669 [inline]
ppp_sync_receive+0xff/0x680 drivers/net/ppp/ppp_synctty.c:334
tty_ldisc_receive_buf+0x14c/0x180 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x70/0xb0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x261/0x780 drivers/tty/tty_buffer.c:494
process_one_work+0x884/0x15c0 kernel/workqueue.c:2630
With call
ioctl$PPPIOCSMRU1(r1, 0x40047452, &(0x7f0000000100)=0x5e6417a8)
Similar code exists in other drivers that implement ppp_channel_ops
ioctl PPPIOCSMRU. Those might also be in scope. Notably excluded from
this are pppol2tp_ioctl and pppoe_ioctl.
This code goes back to the start of git history.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+6177e1f90d92583bcc58@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
---
drivers/net/ppp/ppp_synctty.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c
index ea261a628786..52d05ce4a281 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -453,6 +453,10 @@ ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
case PPPIOCSMRU:
if (get_user(val, (int __user *) argp))
break;
+ if (val > U16_MAX) {
+ err = -EINVAL;
+ break;
+ }
if (val < PPP_MRU)
val = PPP_MRU;
ap->mru = val;
--
2.43.0.rc0.421.g78406f8d94-goog
