Description

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

arp: Prevent overflow in arp_req_get().

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

When ioctl(SIOCGARP) is issued, arp_req_get() looks up an neighbour
entry and copies neigh->ha to struct arpreq.arp_ha.sa_data.

The arp_ha here is struct sockaddr, not struct sockaddr_storage, so
the sa_data buffer is just 14 bytes.

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

However, when dev->addr_len is greater than 22 (e.g. MAX_ADDR_LEN),
arp_netmask is overwritten, which could be set as htonl(0xFFFFFFFFUL)
in arp_ioctl() before calling arp_req_get().

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

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

[0]:
memcpy: detected field-spanning write (size 16) of single field "r->arp_ha.sa_data" at net/ipv4/arp.c:1128 (size 14)
WARNING: CPU: 0 PID: 144638 at net/ipv4/arp.c:1128 arp_req_get+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:arp_req_get+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 ...

Classification

CVE ID: CVE-2024-26733

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 12.41% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/dbc9b22d0ed319b4e29034ce0a3fe32a3ee2c587
https://git.kernel.org/stable/c/97eaa2955db4120ce6ec2ef123e860bc32232c50
https://git.kernel.org/stable/c/f119f2325ba70cbfdec701000dcad4d88805d5b0
https://git.kernel.org/stable/c/a3f2c083cb575d80a7627baf3339e78fedccbb91
https://git.kernel.org/stable/c/3ab0d6f8289ba8402ca95a9fc61a34909d5e1f3a
https://git.kernel.org/stable/c/a7d6027790acea24446ddd6632d394096c0f4667

Timeline