CVE-2022-49142

In the Linux kernel, the following vulnerability has been resolved:

net: preserve skbendoffset() in skbunclonekeeptruesize()

syzbot found another way to trigger the infamous WARNONONCE(delta < len) in skbtrycoalesce() [1]

I was able to root cause the issue to kfence.

When kfence is in action, the following assertion is no longer true:

int size = xxxx; void *ptr1 = kmalloc(size, gfp); void *ptr2 = kmalloc(size, gfp);

if (ptr1 && ptr2) ASSERT(ksize(ptr1) == ksize(ptr2));

We attempted to fix these issues in the blamed commits, but forgot that TCP was possibly shifting data after skbunclonekeeptruesize() has been used, notably from tcpretranstry_collapse().

So we not only need to keep same skb->truesize value, we also need to make sure TCP wont fill new tailroom that pskbexpandhead() was able to get from a addr = kmalloc(...) followed by ksize(addr)

Split skbunclonekeeptruesize() into two parts:

1) Inline skbunclonekeeptruesize() for the common case, when skb is not cloned.

2) Out of line __skbunclonekeeptruesize() for the 'slow path'.

WARNING: CPU: 1 PID: 6490 at net/core/skbuff.c:5295 skbtrycoalesce+0x1235/0x1560 net/core/skbuff.c:5295 Modules linked in: CPU: 1 PID: 6490 Comm: syz-executor161 Not tainted 5.17.0-rc4-syzkaller-00229-g4f12b742eb2b #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:skbtrycoalesce+0x1235/0x1560 net/core/skbuff.c:5295 Code: bf 01 00 00 00 0f b7 c0 89 c6 89 44 24 20 e8 62 24 4e fa 8b 44 24 20 83 e8 01 0f 85 e5 f0 ff ff e9 87 f4 ff ff e8 cb 20 4e fa <0f> 0b e9 06 f9 ff ff e8 af b2 95 fa e9 69 f0 ff ff e8 95 b2 95 fa RSP: 0018:ffffc900063af268 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 00000000ffffffd5 RCX: 0000000000000000 RDX: ffff88806fc05700 RSI: ffffffff872abd55 RDI: 0000000000000003 RBP: ffff88806e675500 R08: 00000000ffffffd5 R09: 0000000000000000 R10: ffffffff872ab659 R11: 0000000000000000 R12: ffff88806dd554e8 R13: ffff88806dd9bac0 R14: ffff88806dd9a2c0 R15: 0000000000000155 FS: 00007f18014f9700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020002000 CR3: 000000006be7a000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> tcptrycoalesce net/ipv4/tcpinput.c:4651 [inline] tcptrycoalesce+0x393/0x920 net/ipv4/tcpinput.c:4630 tcpqueuercv+0x8a/0x6e0 net/ipv4/tcpinput.c:4914 tcpdataqueue+0x11fd/0x4bb0 net/ipv4/tcpinput.c:5025 tcprcvestablished+0x81e/0x1ff0 net/ipv4/tcpinput.c:5947 tcpv4dorcv+0x65e/0x980 net/ipv4/tcpipv4.c:1719 skbacklog_rcv include/net/sock.h:1037 [inline] __releasesock+0x134/0x3b0 net/core/sock.c:2779 releasesock+0x54/0x1b0 net/core/sock.c:3311 skwaitdata+0x177/0x450 net/core/sock.c:2821 tcprecvmsglocked+0xe28/0x1fd0 net/ipv4/tcp.c:2457 tcprecvmsg+0x137/0x610 net/ipv4/tcp.c:2572 inetrecvmsg+0x11b/0x5e0 net/ipv4/afinet.c:850 sockrecvmsgnosec net/socket.c:948 [inline] sockrecvmsg net/socket.c:966 [inline] sock_recvmsg net/socket.c:962 [inline] ____sys_recvmsg+0x2c4/0x600 net/socket.c:2632 ___sys_recvmsg+0x127/0x200 net/socket.c:2674 _sysrecvmsg+0xe2/0x1a0 net/socket.c:2704 dosyscallx64 arch/x86/entry/common.c:50 [inline] dosyscall64+0x35/0xb0 arch/x86/entry/common.c:80 entrySYSCALL64afterhwframe+0x44/0xae