CVE-2026-64450

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

tipc: fix out-of-bounds read in broadcast Gap ACK blocks

A broadcast PROTOCOL/STATE_MSG can carry a Gap ACK blocks record in its

data area. tipc_get_gap_ack_blks() only verifies that the record's len

field is self-consistent with its ugack_cnt/bgack_cnt counts

(sz == struct_size(p, gacks, ugack_cnt + bgack_cnt)); it does not check

that the record actually fits in the message data area, msg_data_sz().

The unicast caller tipc_link_proto_rcv() bounds it ("if (glen > dlen)

break;"), but the broadcast caller tipc_bcast_sync_rcv() discards the

returned size, so tipc_link_advance_transmq() copies the record off the

receive skb with an attacker-controlled count:

this_ga = kmemdup(ga, struct_size(ga, gacks, ga->bgack_cnt),

GFP_ATOMIC);

A TIPC neighbour that negotiated TIPC_GAP_ACK_BLOCK triggers it with one

ordinary broadcast STATE_MSG (msg_bc_ack_invalid() clear), sized so its

data area is short, carrying a Gap ACK record with len = 0x400,

bgack_cnt = 0xff and ugack_cnt = 0. len then equals

struct_size(p, gacks, 255), so the consistency check passes and ga is

non-NULL; kmemdup() reads struct_size(ga, gacks, 255) = 1024 bytes out

of the much smaller skb:

BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x48/0x60

Read of size 1024 at addr ffff0000c7030d38 by task poc864/69

Call trace:

kmemdup_noprof+0x48/0x60

tipc_link_advance_transmq+0x86c/0xb80

tipc_link_bc_ack_rcv+0x19c/0x1e0

tipc_bcast_sync_rcv+0x1c4/0x2c4

tipc_rcv+0x85c/0x1340

tipc_l2_rcv_msg+0xac/0x104

The buggy address belongs to the object at ffff0000c7030d00

which belongs to the cache skbuff_small_head of size 704

The buggy address is located 56 bytes inside of

allocated 704-byte region [ffff0000c7030d00, ffff0000c7030fc0)

The copied-out bytes are subsequently consumed as gap/ack values, but

the read is already out of bounds at the kmemdup() regardless of how

they are used.

The unicast STATE path drops such a message: "if (glen > dlen) break;"

skips the rest of STATE_MSG handling and the skb is freed. Make the

broadcast path drop it too. tipc_bcast_sync_rcv() now bounds the record

against msg_data_sz() and, when it does not fit, reports it back through

tipc_node_bc_sync_rcv() to tipc_rcv() so the skb is discarded rather than

processed. ga is not cleared on this path: ga == NULL already means

"legacy peer without Selective ACK", a distinct legitimate state.