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Subject[PATCH 4.17 19/66] net: skb_segment() should not return NULL
Date
4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit ff907a11a0d68a749ce1a321f4505c03bf72190c ]

syzbot caught a NULL deref [1], caused by skb_segment()

skb_segment() has many "goto err;" that assume the @err variable
contains -ENOMEM.

A successful call to __skb_linearize() should not clear @err,
otherwise a subsequent memory allocation error could return NULL.

While we are at it, we might use -EINVAL instead of -ENOMEM when
MAX_SKB_FRAGS limit is reached.

[1]
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 0 PID: 13285 Comm: syz-executor3 Not tainted 4.18.0-rc4+ #146
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:tcp_gso_segment+0x3dc/0x1780 net/ipv4/tcp_offload.c:106
Code: f0 ff ff 0f 87 1c fd ff ff e8 00 88 0b fb 48 8b 75 d0 48 b9 00 00 00 00 00 fc ff df 48 8d be 90 00 00 00 48 89 f8 48 c1 e8 03 <0f> b6 14 08 48 8d 86 94 00 00 00 48 89 c6 83 e0 07 48 c1 ee 03 0f
RSP: 0018:ffff88019b7fd060 EFLAGS: 00010206
RAX: 0000000000000012 RBX: 0000000000000020 RCX: dffffc0000000000
RDX: 0000000000040000 RSI: 0000000000000000 RDI: 0000000000000090
RBP: ffff88019b7fd0f0 R08: ffff88019510e0c0 R09: ffffed003b5c46d6
R10: ffffed003b5c46d6 R11: ffff8801dae236b3 R12: 0000000000000001
R13: ffff8801d6c581f4 R14: 0000000000000000 R15: ffff8801d6c58128
FS: 00007fcae64d6700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004e8664 CR3: 00000001b669b000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
tcp4_gso_segment+0x1c3/0x440 net/ipv4/tcp_offload.c:54
inet_gso_segment+0x64e/0x12d0 net/ipv4/af_inet.c:1342
inet_gso_segment+0x64e/0x12d0 net/ipv4/af_inet.c:1342
skb_mac_gso_segment+0x3b5/0x740 net/core/dev.c:2792
__skb_gso_segment+0x3c3/0x880 net/core/dev.c:2865
skb_gso_segment include/linux/netdevice.h:4099 [inline]
validate_xmit_skb+0x640/0xf30 net/core/dev.c:3104
__dev_queue_xmit+0xc14/0x3910 net/core/dev.c:3561
dev_queue_xmit+0x17/0x20 net/core/dev.c:3602
neigh_hh_output include/net/neighbour.h:473 [inline]
neigh_output include/net/neighbour.h:481 [inline]
ip_finish_output2+0x1063/0x1860 net/ipv4/ip_output.c:229
ip_finish_output+0x841/0xfa0 net/ipv4/ip_output.c:317
NF_HOOK_COND include/linux/netfilter.h:276 [inline]
ip_output+0x223/0x880 net/ipv4/ip_output.c:405
dst_output include/net/dst.h:444 [inline]
ip_local_out+0xc5/0x1b0 net/ipv4/ip_output.c:124
iptunnel_xmit+0x567/0x850 net/ipv4/ip_tunnel_core.c:91
ip_tunnel_xmit+0x1598/0x3af1 net/ipv4/ip_tunnel.c:778
ipip_tunnel_xmit+0x264/0x2c0 net/ipv4/ipip.c:308
__netdev_start_xmit include/linux/netdevice.h:4148 [inline]
netdev_start_xmit include/linux/netdevice.h:4157 [inline]
xmit_one net/core/dev.c:3034 [inline]
dev_hard_start_xmit+0x26c/0xc30 net/core/dev.c:3050
__dev_queue_xmit+0x29ef/0x3910 net/core/dev.c:3569
dev_queue_xmit+0x17/0x20 net/core/dev.c:3602
neigh_direct_output+0x15/0x20 net/core/neighbour.c:1403
neigh_output include/net/neighbour.h:483 [inline]
ip_finish_output2+0xa67/0x1860 net/ipv4/ip_output.c:229
ip_finish_output+0x841/0xfa0 net/ipv4/ip_output.c:317
NF_HOOK_COND include/linux/netfilter.h:276 [inline]
ip_output+0x223/0x880 net/ipv4/ip_output.c:405
dst_output include/net/dst.h:444 [inline]
ip_local_out+0xc5/0x1b0 net/ipv4/ip_output.c:124
ip_queue_xmit+0x9df/0x1f80 net/ipv4/ip_output.c:504
tcp_transmit_skb+0x1bf9/0x3f10 net/ipv4/tcp_output.c:1168
tcp_write_xmit+0x1641/0x5c20 net/ipv4/tcp_output.c:2363
__tcp_push_pending_frames+0xb2/0x290 net/ipv4/tcp_output.c:2536
tcp_push+0x638/0x8c0 net/ipv4/tcp.c:735
tcp_sendmsg_locked+0x2ec5/0x3f00 net/ipv4/tcp.c:1410
tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1447
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:641 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:651
__sys_sendto+0x3d7/0x670 net/socket.c:1797
__do_sys_sendto net/socket.c:1809 [inline]
__se_sys_sendto net/socket.c:1805 [inline]
__x64_sys_sendto+0xe1/0x1a0 net/socket.c:1805
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455ab9
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fcae64d5c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fcae64d66d4 RCX: 0000000000455ab9
RDX: 0000000000000001 RSI: 0000000020000200 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000014
R13: 00000000004c1145 R14: 00000000004d1818 R15: 0000000000000006
Modules linked in:
Dumping ftrace buffer:
(ftrace buffer empty)

Fixes: ddff00d42043 ("net: Move skb_has_shared_frag check out of GRE code and into segmentation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/skbuff.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3705,6 +3705,7 @@ normal:
net_warn_ratelimited(
"skb_segment: too many frags: %u %u\n",
pos, mss);
+ err = -EINVAL;
goto err;
}

@@ -3738,11 +3739,10 @@ skip_fraglist:

perform_csum_check:
if (!csum) {
- if (skb_has_shared_frag(nskb)) {
- err = __skb_linearize(nskb);
- if (err)
- goto err;
- }
+ if (skb_has_shared_frag(nskb) &&
+ __skb_linearize(nskb))
+ goto err;
+
if (!nskb->remcsum_offload)
nskb->ip_summed = CHECKSUM_NONE;
SKB_GSO_CB(nskb)->csum =

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