CVE-2026-98525

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).