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.
