mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

Overview

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

mctp: route: iterate socket tag list in mctp_lookup_prealloc_tag()

When a socket transmits a packet with MCTP_TAG_PREALLOC set, mctp_lookup_prealloc_tag() iterates over the per-netns &mns->keys list and matches netid, req_tag, peer_addr, and manual_alloc, without checking whether tmp->sk == &msk->sk. This allows any MCTP socket in the same network namespace to use and consume another socket's preallocated tag.

Iterate the socket's own tag list (&msk->keys via sklist) instead of the namespace-wide &mns->keys list in mctp_lookup_prealloc_tag(), ensuring that only tags allocated by msk are matched.

Tested in QEMU against Linux 7.3.0-rc3 by allocating a manual tag (0x18) on socket A via SIOCMCTPALLOCTAG for peer EID 9 and sending a 4-byte message with MCTP_TAG_PREALLOC from socket B in the same network namespace. On the unfixed kernel, sendto(sock_b) using socket A's preallocated tag succeeds (ret = 4); with this patch applied, sendto(sock_b) fails with -ENOENT (errno = 2) while sendto(sock_a) succeeds (ret = 4).

Affected

• Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < 09299addab11857e92eca55cd8ef3350b927c90c
• Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < e35cb500dd14882f8dee61783fccd1823fd3ab0d
• Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < f178300e2f56ca9ec2a3a0090608730bbee0af7b
• Linux >= 63ed1aab3d40aa61aaa66819bdce9377ac7f40fa < 26cc0e69cce062cd3aa6fae33074684669c35a71
• Linux 5.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.