CVE-2022-49142

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

net: preserve skb_end_offset() in skb_unclone_keeptruesize()

syzbot found another way to trigger the infamous WARN_ON_ONCE(delta < len)

in skb_try_coalesce() [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 skb_unclone_keeptruesize()

has been used, notably from tcp_retrans_try_collapse().

So we not only need to keep same skb->truesize value,

we also need to make sure TCP wont fill new tailroom

that pskb_expand_head() was able to get from a

addr = kmalloc(...) followed by ksize(addr)

Split skb_unclone_keeptruesize() into two parts:

1) Inline skb_unclone_keeptruesize() for the common case,

when skb is not cloned.

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

WARNING: CPU: 1 PID: 6490 at net/core/skbuff.c:5295 skb_try_coalesce+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:skb_try_coalesce+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>

tcp_try_coalesce net/ipv4/tcp_input.c:4651 [inline]

tcp_try_coalesce+0x393/0x920 net/ipv4/tcp_input.c:4630

tcp_queue_rcv+0x8a/0x6e0 net/ipv4/tcp_input.c:4914

tcp_data_queue+0x11fd/0x4bb0 net/ipv4/tcp_input.c:5025

tcp_rcv_established+0x81e/0x1ff0 net/ipv4/tcp_input.c:5947

tcp_v4_do_rcv+0x65e/0x980 net/ipv4/tcp_ipv4.c:1719

sk_backlog_rcv include/net/sock.h:1037 [inline]

__release_sock+0x134/0x3b0 net/core/sock.c:2779

release_sock+0x54/0x1b0 net/core/sock.c:3311

sk_wait_data+0x177/0x450 net/core/sock.c:2821

tcp_recvmsg_locked+0xe28/0x1fd0 net/ipv4/tcp.c:2457

tcp_recvmsg+0x137/0x610 net/ipv4/tcp.c:2572

inet_recvmsg+0x11b/0x5e0 net/ipv4/af_inet.c:850

sock_recvmsg_nosec net/socket.c:948 [inline]

sock_recvmsg 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

__sys_recvmsg+0xe2/0x1a0 net/socket.c:2704

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x44/0xae