From: Eric Dumazet edumazet@google.com
[ Upstream commit 501a90c945103e8627406763dac418f20f3837b2 ]
syzbot was once again able to crash a host by setting a very small mtu on loopback device.
Let's make inetdev_valid_mtu() available in include/net/ip.h, and use it in ip_setup_cork(), so that we protect both ip_append_page() and __ip_append_data()
Also add a READ_ONCE() when the device mtu is read.
Pairs this lockless read with one WRITE_ONCE() in __dev_set_mtu(), even if other code paths might write over this field.
Add a big comment in include/linux/netdevice.h about dev->mtu needing READ_ONCE()/WRITE_ONCE() annotations.
Hopefully we will add the missing ones in followup patches.
[1]
refcount_t: saturated; leaking memory. WARNING: CPU: 0 PID: 9464 at lib/refcount.c:22 refcount_warn_saturate+0x138/0x1f0 lib/refcount.c:22 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 9464 Comm: syz-executor850 Not tainted 5.4.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x197/0x210 lib/dump_stack.c:118 panic+0x2e3/0x75c kernel/panic.c:221 __warn.cold+0x2f/0x3e kernel/panic.c:582 report_bug+0x289/0x300 lib/bug.c:195 fixup_bug arch/x86/kernel/traps.c:174 [inline] fixup_bug arch/x86/kernel/traps.c:169 [inline] do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286 invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027 RIP: 0010:refcount_warn_saturate+0x138/0x1f0 lib/refcount.c:22 Code: 06 31 ff 89 de e8 c8 f5 e6 fd 84 db 0f 85 6f ff ff ff e8 7b f4 e6 fd 48 c7 c7 e0 71 4f 88 c6 05 56 a6 a4 06 01 e8 c7 a8 b7 fd <0f> 0b e9 50 ff ff ff e8 5c f4 e6 fd 0f b6 1d 3d a6 a4 06 31 ff 89 RSP: 0018:ffff88809689f550 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff815e4336 RDI: ffffed1012d13e9c RBP: ffff88809689f560 R08: ffff88809c50a3c0 R09: fffffbfff15d31b1 R10: fffffbfff15d31b0 R11: ffffffff8ae98d87 R12: 0000000000000001 R13: 0000000000040100 R14: ffff888099041104 R15: ffff888218d96e40 refcount_add include/linux/refcount.h:193 [inline] skb_set_owner_w+0x2b6/0x410 net/core/sock.c:1999 sock_wmalloc+0xf1/0x120 net/core/sock.c:2096 ip_append_page+0x7ef/0x1190 net/ipv4/ip_output.c:1383 udp_sendpage+0x1c7/0x480 net/ipv4/udp.c:1276 inet_sendpage+0xdb/0x150 net/ipv4/af_inet.c:821 kernel_sendpage+0x92/0xf0 net/socket.c:3794 sock_sendpage+0x8b/0xc0 net/socket.c:936 pipe_to_sendpage+0x2da/0x3c0 fs/splice.c:458 splice_from_pipe_feed fs/splice.c:512 [inline] __splice_from_pipe+0x3ee/0x7c0 fs/splice.c:636 splice_from_pipe+0x108/0x170 fs/splice.c:671 generic_splice_sendpage+0x3c/0x50 fs/splice.c:842 do_splice_from fs/splice.c:861 [inline] direct_splice_actor+0x123/0x190 fs/splice.c:1035 splice_direct_to_actor+0x3b4/0xa30 fs/splice.c:990 do_splice_direct+0x1da/0x2a0 fs/splice.c:1078 do_sendfile+0x597/0xd00 fs/read_write.c:1464 __do_sys_sendfile64 fs/read_write.c:1525 [inline] __se_sys_sendfile64 fs/read_write.c:1511 [inline] __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x441409 Code: e8 ac e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fffb64c4f78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441409 RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000005 RBP: 0000000000073b8a R08: 0000000000000010 R09: 0000000000000010 R10: 0000000000010001 R11: 0000000000000246 R12: 0000000000402180 R13: 0000000000402210 R14: 0000000000000000 R15: 0000000000000000 Kernel Offset: disabled Rebooting in 86400 seconds..
Fixes: 1470ddf7f8ce ("inet: Remove explicit write references to sk/inet in ip_append_data") Signed-off-by: Eric Dumazet edumazet@google.com Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/netdevice.h | 5 +++++ include/net/ip.h | 5 +++++ net/core/dev.c | 3 ++- net/ipv4/devinet.c | 5 ----- net/ipv4/ip_output.c | 14 +++++++++----- 5 files changed, 21 insertions(+), 11 deletions(-)
--- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -1617,6 +1617,11 @@ struct net_device { unsigned char if_port; unsigned char dma;
+ /* Note : dev->mtu is often read without holding a lock. + * Writers usually hold RTNL. + * It is recommended to use READ_ONCE() to annotate the reads, + * and to use WRITE_ONCE() to annotate the writes. + */ unsigned int mtu; unsigned short type; unsigned short hard_header_len; --- a/include/net/ip.h +++ b/include/net/ip.h @@ -596,4 +596,9 @@ extern int sysctl_icmp_msgs_burst; int ip_misc_proc_init(void); #endif
+static inline bool inetdev_valid_mtu(unsigned int mtu) +{ + return likely(mtu >= IPV4_MIN_MTU); +} + #endif /* _IP_H */ --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6126,7 +6126,8 @@ static int __dev_set_mtu(struct net_devi if (ops->ndo_change_mtu) return ops->ndo_change_mtu(dev, new_mtu);
- dev->mtu = new_mtu; + /* Pairs with all the lockless reads of dev->mtu in the stack */ + WRITE_ONCE(dev->mtu, new_mtu); return 0; }
--- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -1364,11 +1364,6 @@ skip: } }
-static bool inetdev_valid_mtu(unsigned int mtu) -{ - return mtu >= IPV4_MIN_MTU; -} - static void inetdev_send_gratuitous_arp(struct net_device *dev, struct in_device *in_dev)
--- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -1145,13 +1145,17 @@ static int ip_setup_cork(struct sock *sk rt = *rtp; if (unlikely(!rt)) return -EFAULT; - /* - * We steal reference to this route, caller should not release it - */ - *rtp = NULL; + cork->fragsize = ip_sk_use_pmtu(sk) ? - dst_mtu(&rt->dst) : rt->dst.dev->mtu; + dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu); + + if (!inetdev_valid_mtu(cork->fragsize)) + return -ENETUNREACH; + cork->dst = &rt->dst; + /* We stole this route, caller should not release it. */ + *rtp = NULL; + cork->length = 0; cork->ttl = ipc->ttl; cork->tos = ipc->tos;