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. tipcgetgapackblks() only verifies that the record's len

field is self-consistent with its ugackcnt/bgackcnt counts

(sz == structsize(p, gacks, ugackcnt + bgack_cnt)); it does not check

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

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

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

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

receive skb with an attacker-controlled count:

thisga = kmemdup(ga, structsize(ga, gacks, ga->bgack_cnt),

  GFP_ATOMIC);

A TIPC neighbour that negotiated TIPCGAPACK_BLOCK triggers it with one

ordinary broadcast STATEMSG (msgbcackinvalid() clear), sized so its

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

bgackcnt = 0xff and ugackcnt = 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

   tipclinkadvance_transmq+0x86c/0xb80

   tipclinkbcackrcv+0x19c/0x1e0

   tipcbcastsync_rcv+0x1c4/0x2c4

   tipc_rcv+0x85c/0x1340

   tipcl2rcv_msg+0xac/0x104

  The buggy address belongs to the object at ffff0000c7030d00

   which belongs to the cache skbuffsmallhead 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. tipcbcastsync_rcv() now bounds the record

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

tipcnodebcsyncrcv() 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.