6.6-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ Upstream commit ae633388cae349886f1a3cfb27aa092854b24c1b ]
I accidentally added a bug in pptp_xmit() that syzbot caught for us.
Only call ip_rt_put() if a route has been allocated.
BUG: unable to handle page fault for address: ffffffffffffffdb PGD df3b067 P4D df3b067 PUD df3d067 PMD 0 Oops: Oops: 0002 [#1] SMP KASAN PTI CPU: 1 UID: 0 PID: 6346 Comm: syz.0.336 Not tainted 6.16.0-next-20250804-syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:arch_atomic_add_return arch/x86/include/asm/atomic.h:85 [inline] RIP: 0010:raw_atomic_sub_return_release include/linux/atomic/atomic-arch-fallback.h:846 [inline] RIP: 0010:atomic_sub_return_release include/linux/atomic/atomic-instrumented.h:327 [inline] RIP: 0010:__rcuref_put include/linux/rcuref.h:109 [inline] RIP: 0010:rcuref_put+0x172/0x210 include/linux/rcuref.h:173 Call Trace: <TASK> dst_release+0x24/0x1b0 net/core/dst.c:167 ip_rt_put include/net/route.h:285 [inline] pptp_xmit+0x14b/0x1a90 drivers/net/ppp/pptp.c:267 __ppp_channel_push+0xf2/0x1c0 drivers/net/ppp/ppp_generic.c:2166 ppp_channel_push+0x123/0x660 drivers/net/ppp/ppp_generic.c:2198 ppp_write+0x2b0/0x400 drivers/net/ppp/ppp_generic.c:544 vfs_write+0x27b/0xb30 fs/read_write.c:684 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fixes: de9c4861fb42 ("pptp: ensure minimal skb length in pptp_xmit()") Reported-by: syzbot+27d7cfbc93457e472e00@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/689095a5.050a0220.1fc43d.0009.GAE@google.com/ Signed-off-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20250807142146.2877060-1-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ppp/pptp.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c index 4455d99be767..3a10303eb756 100644 --- a/drivers/net/ppp/pptp.c +++ b/drivers/net/ppp/pptp.c @@ -159,17 +159,17 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb) int len; unsigned char *data; __u32 seq_recv; - struct rtable *rt = NULL; + struct rtable *rt; struct net_device *tdev; struct iphdr *iph; int max_headroom;
if (sk_pppox(po)->sk_state & PPPOX_DEAD) - goto tx_error; + goto tx_drop;
rt = pptp_route_output(po, &fl4); if (IS_ERR(rt)) - goto tx_error; + goto tx_drop;
tdev = rt->dst.dev;
@@ -265,6 +265,7 @@ static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
tx_error: ip_rt_put(rt); +tx_drop: kfree_skb(skb); return 1; }