CVE-2024-26733: arp: Prevent overflow in arp_req_get().

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

arp: Prevent overflow in arpreqget().

syzkaller reported an overflown write in arpreqget(). [0]

When ioctl(SIOCGARP) is issued, arpreqget() looks up an neighbour entry and copies neigh->ha to struct arpreq.arpha.sadata.

The arpha here is struct sockaddr, not struct sockaddrstorage, so the sadata buffer is just 14 bytes.

In the splat below, 2 bytes are overflown to the next int field, arpflags. We initialise the field just after the memcpy(), so it's not a problem.

However, when dev->addrlen is greater than 22 (e.g. MAXADDRLEN), arpnetmask is overwritten, which could be set as htonl(0xFFFFFFFFUL) in arpioctl() before calling arpreqget().

To avoid the overflow, let's limit the max length of memcpy().

Note that commit b5f0de6df6dc ("net: dev: Convert sadata to flexible array in struct sockaddr") just silenced syzkaller.

[0]: memcpy: detected field-spanning write (size 16) of single field "r->arpha.sadata" at net/ipv4/arp.c:1128 (size 14) WARNING: CPU: 0 PID: 144638 at net/ipv4/arp.c:1128 arpreqget+0x411/0x4a0 net/ipv4/arp.c:1128 Modules linked in: CPU: 0 PID: 144638 Comm: syz-executor.4 Not tainted 6.1.74 #31 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-5 04/01/2014 RIP: 0010:arpreqget+0x411/0x4a0 net/ipv4/arp.c:1128 Code: fd ff ff e8 41 42 de fb b9 0e 00 00 00 4c 89 fe 48 c7 c2 20 6d ab 87 48 c7 c7 80 6d ab 87 c6 05 25 af 72 04 01 e8 5f 8d ad fb <0f> 0b e9 6c fd ff ff e8 13 42 de fb be 03 00 00 00 4c 89 e7 e8 a6 RSP: 0018:ffffc900050b7998 EFLAGS: 00010286 RAX: 0000000000000000 RBX: ffff88803a815000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff8641a44a RDI: 0000000000000001 RBP: ffffc900050b7a98 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 203a7970636d656d R12: ffff888039c54000 R13: 1ffff92000a16f37 R14: ffff88803a815084 R15: 0000000000000010 FS: 00007f172bf306c0(0000) GS:ffff88805aa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f172b3569f0 CR3: 0000000057f12005 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> arpioctl+0x33f/0x4b0 net/ipv4/arp.c:1261 inetioctl+0x314/0x3a0 net/ipv4/afinet.c:981 sockdoioctl+0xdf/0x260 net/socket.c:1204 sockioctl+0x3ef/0x650 net/socket.c:1321 vfsioctl fs/ioctl.c:51 [inline] dosysioctl fs/ioctl.c:870 [inline] sesysioctl fs/ioctl.c:856 [inline] x64sysioctl+0x18e/0x220 fs/ioctl.c:856 dosyscallx64 arch/x86/entry/common.c:51 [inline] dosyscall64+0x37/0x90 arch/x86/entry/common.c:81 entrySYSCALL64afterhwframe+0x64/0xce RIP: 0033:0x7f172b262b8d Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 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:00007f172bf300b8 EFLAGS: 00000246 ORIGRAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f172b3abf80 RCX: 00007f172b262b8d RDX: 0000000020000000 RSI: 0000000000008954 RDI: 0000000000000003 RBP: 00007f172b2d3493 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 000000000000000b R14: 00007f172b3abf80 R15: 00007f172bf10000 </TASK>

— MITRE

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

arp: Prevent overflow in arpreqget().

The Linux kernel CVE team has assigned CVE-2024-26733 to this issue.

Upstream advisory: https://lore.kernel.org/linux-cve-announce/2024040358-CVE-2024-26733-617f@gregkh/T

— Red Hat