5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet edumazet@google.com
[ Upstream commit de9c4861fb42f0cd72da844c3c34f692d5895b7b ]
Commit aabc6596ffb3 ("net: ppp: Add bound checking for skb data on ppp_sync_txmung") fixed ppp_sync_txmunge()
We need a similar fix in pptp_xmit(), otherwise we might read uninit data as reported by syzbot.
BUG: KMSAN: uninit-value in pptp_xmit+0xc34/0x2720 drivers/net/ppp/pptp.c:193 pptp_xmit+0xc34/0x2720 drivers/net/ppp/pptp.c:193 ppp_channel_bridge_input drivers/net/ppp/ppp_generic.c:2290 [inline] ppp_input+0x1d6/0xe60 drivers/net/ppp/ppp_generic.c:2314 pppoe_rcv_core+0x1e8/0x760 drivers/net/ppp/pppoe.c:379 sk_backlog_rcv+0x142/0x420 include/net/sock.h:1148 __release_sock+0x1d3/0x330 net/core/sock.c:3213 release_sock+0x6b/0x270 net/core/sock.c:3767 pppoe_sendmsg+0x15d/0xcb0 drivers/net/ppp/pppoe.c:904 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x330/0x3d0 net/socket.c:727 ____sys_sendmsg+0x893/0xd80 net/socket.c:2566 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2620 __sys_sendmmsg+0x2d9/0x7c0 net/socket.c:2709
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+afad90ffc8645324afe5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68887d86.a00a0220.b12ec.00cd.GAE@google.com/T... Signed-off-by: Eric Dumazet edumazet@google.com Reviewed-by: Dawid Osuchowski dawid.osuchowski@linux.intel.com Link: https://patch.msgid.link/20250729080207.1863408-1-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ppp/pptp.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c index e1fabb3e3246..5e2f4702aa2b 100644 --- a/drivers/net/ppp/pptp.c +++ b/drivers/net/ppp/pptp.c @@ -141,9 +141,7 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) int len; unsigned char *data; __u32 seq_recv; - - - struct rtable *rt; + struct rtable *rt = NULL; struct net_device *tdev; struct iphdr *iph; int max_headroom; @@ -165,16 +163,20 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) { struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom); - if (!new_skb) { - ip_rt_put(rt); + + if (!new_skb) goto tx_error; - } + if (skb->sk) skb_set_owner_w(new_skb, skb->sk); consume_skb(skb); skb = new_skb; }
+ /* Ensure we can safely access protocol field and LCP code */ + if (!pskb_may_pull(skb, 3)) + goto tx_error; + data = skb->data; islcp = ((data[0] << 8) + data[1]) == PPP_LCP && 1 <= data[2] && data[2] <= 7;
@@ -248,6 +250,7 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) return 1;
tx_error: + ip_rt_put(rt); kfree_skb(skb); return 1; }