CVE-2026-68297tipc: fix u16 MTU truncation in media and bearer MTU validation

Official description

In the Linux kernel, the following vulnerability has been resolved: tipc: fix u16 MTU truncation in media and bearer MTU validation Both TIPC_NL_MEDIA_SET and TIPC_NL_BEARER_SET accept user-supplied MTU values but only enforce a minimum bound, not a maximum. When a user sets the MTU to a value exceeding U16_MAX (65535), it passes validation but is silently truncated when assigned to u16 fields l->mtu and l->advertised_mtu in tipc_link_create(). Values like 65536 (0x10000) truncate to 0, causing a division by zero in tipc_link_set_queue_limits() which computes TIPC_MAX_PUBL / (l->mtu / ITEM_SIZE). Other overflowing values (e.g. 65537-131071) produce small incorrect MTU values, resulting in link malfunction behaviors. Crash stack (triggered as unprivileged user via user namespace): tipc_link_set_queue_limits net/tipc/link.c:2531 tipc_link_create net/tipc/link.c:520 tipc_node_check_dest net/tipc/node.c:1279 tipc_disc_rcv net/tipc/discover.c:252 tipc_rcv net/tipc/node.c:2129 tipc_udp_recv net/tipc/udp_media.c:392 Two independent paths lack the upper bound check: 1. tipc_udp_mtu_bad() -- called from __tipc_nl_media_set() (MEDIA_SET) 2. inline check in __tipc_nl_bearer_set() at bearer.c:1160 (BEARER_SET) Fix both by rejecting MTU values above U16_MAX.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8bfdfe0dbb36a650b7c4dec1aeae078319938a0b
• https://git.kernel.org/stable/c/dc4b577a083b361d25e118dc96d8281255ebe22c
• https://git.kernel.org/stable/c/dfdfd987f1917c84766e097a6120a1f3f1634940
• https://git.kernel.org/stable/c/f02334a9e378f7e07232b26dc3d2ab353339f040
• https://git.kernel.org/stable/c/f4013598b69457dbea350df52e52daea6faef8eb
• https://git.kernel.org/stable/c/1b8fb5a20508bfb0db854e01214888c761b3a911
• https://git.kernel.org/stable/c/c1cda72f6acec02ebd45d913bf8527ff77336ba6
• https://git.kernel.org/stable/c/9f29cd8a8e7901a2617c8064ce9f50fc67b97cb8