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

Overview

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.

Affected

• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 055663d21dc4336f67933ab26bef3c5934be6324
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 016f5995c37a5a2c45198308f830f244517d70b7
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 74b45af86a767594ba52330cd440ea84e24d700d
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 9a51115fcdc78687c8852bf93a1db3951dbb223b
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < a21ed5064217cc33726da6c7ef1a520eba43aea1
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 2de42e268174766cb2e2b90721afdfdff70e0d8d
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < f333b6851bdf326fd2134133272dbbed0c94d921
• Linux >= d7626b5acff9227e2a65da636a53e09bdafdc0aa < 2b66974a1b6134a4bbc3bfed181f7418f688eb54
• Linux 5.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.