CVE-2026-68297

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.