CVE: CVE-2023-52435
Published: 2024-02-20
Description: In the Linux kernel, the following vulnerability has been resolved:

net: prevent mss overflow in skb_segment()

Once again syzbot is able to crash the kernel in skb_segment() [1]

GSO_BY_FRAGS is a forbidden value, but unfortunately the following
computation in skb_segment() can reach it quite easily :

	mss = mss * partial_segs;

65535 = 3 * 5 * 17 * 257, so many initial values of mss can lead to
a bad final result.

Make sure to limit segmentation so that the new mss value is smaller
than GSO_BY_FRAGS.

[1]

general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x[PII_REDACTED]000070-0x[PII_REDACTED]000077]
CPU: 1 PID: 5079 Comm: syz-executor993 Not tainted 6.7.0-rc4-syzkaller-00141-g1ae4cd3cbdd0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
RIP: 0010:skb_segment+0x181d/0x3f30 net/core/skbuff.c:4551
Code: 83 e3 02 e9 fb ed ff ff e8 90 68 1c f9 48 8b 84 24 f8 00 00 00 48 8d 78 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8a 21 00 00 48 8b 84 24 f8 00
RSP: 0018:ffffc900043473d0 EFLAGS: 00010202
RAX: dffffc[PII_REDACTED] RBX: [PII_REDACTED] RCX: ffffffff886b1597
RDX:[PII_REDACTED]00000e RSI: ffffffff886b2520 RDI: [PII_REDACTED]
RBP: ffffc[PII_REDACTED]8 R08: [PII_REDACTED] R09:[PII_REDACTED]00ffff
R10:[PII_REDACTED]00ffff R11: [PII_REDACTED] R12: ffff888063202ac0
R13: [PII_REDACTED] R14:[PII_REDACTED]00ffff R15: [PII_REDACTED]
FS:[PII_REDACTED]e7e380(0000) GS:ffff8880b9900000(0000) knlGS:[PII_REDACTED]
CS: 0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2: [PII_REDACTED] CR3:[PII_REDACTED]ee2000 CR4:[PII_REDACTED]3506f0
DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
Call Trace:
<TASK>
udp6_ufo_fragment+0xa0e/0xd00 net/ipv6/udp_offload.c:109
ipv6_gso_segment+0x534/0x17e0 net/ipv6/ip6_offload.c:120
skb_mac_gso_segment+0x290/0x610 net/core/gso.c:53
__skb_gso_segment+0x339/0x710 net/core/gso.c:124
skb_gso_segment include/net/gso.h:83 [inline]
validate_xmit_skb+0x36c/0xeb0 net/core/dev.c:3626
__dev_queue_xmit+0x6f3/0x3d60 net/core/dev.c:4338
dev_queue_xmit include/linux/netdevice.h:3134 [inline]
packet_xmit+0x257/0x380 net/packet/af_packet.c:276
packet_snd net/packet/af_packet.c:3087 [inline]
packet_sendmsg+0x24c6/0x5220 net/packet/af_packet.c:3119
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0xd5/0x180 net/socket.c:745
__sys_sendto+0x255/0x340 net/socket.c:2190
__do_sys_sendto net/socket.c:2202 [inline]
__se_sys_sendto net/socket.c:2198 [inline]
__x64_sys_sendto+0xe0/0x1b0 net/socket.c:2198
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f8692032aa9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 d1 19 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff8d685418 EFLAGS: 00000246 ORIG_RAX:[PII_REDACTED]00002c
RAX: ffffffffffffffda RBX: [PII_REDACTED] RCX: 00007f8692032aa9
RDX: [PII_REDACTED] RSI:[PII_REDACTED]0000c0 RDI: [PII_REDACTED]
RBP:[PII_REDACTED]0f4240 R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: 00007fff8d685480
R13: [PII_REDACTED] R14: 00007fff8d685480 R15: [PII_REDACTED]
</TASK>
Modules linked in:
---[ end trace [PII_REDACTED] ]---
RIP: 0010:skb_segment+0x181d/0x3f30 net/core/skbuff.c:4551
Code: 83 e3 02 e9 fb ed ff ff e8 90 68 1c f9 48 8b 84 24 f8 00 00 00 48 8d 78 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 8a 21 00 00 48 8b 84 24 f8 00
RSP: 0018:ffffc900043473d0 EFLAGS: 00010202
RAX: dffffc[PII_REDACTED] RBX: [PII_REDACTED] RCX: ffffffff886b1597
RDX:[PII_REDACTED]00000e RSI: ffffffff886b2520 RDI: [PII_REDACTED]
RBP: ffffc[PII_REDACTED]8 R0
---truncated---
CVSS Score: 5.5 (MEDIUM)
CWE: CWE-119
References: https://git.kernel.org/stable/c/0d3ffbbf8631d6db0552f[PII_REDACTED]8991c856f; https://git.kernel.org/stable/c/23d05d563b7e7b0314e65c8e882bc27eac2da8e7; https://git.kernel.org/stable/c/6c53e8547687d9c767c139cd4b50af566f58c29a