CVE-2024-26669 net/sched: flower: Fix chain template offload

What is CVE-2024-26669?

CVE-2024-26669 is a high-severity memory corruption vulnerability in Linux kernel, published on 2 Apr 2024. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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

net/sched: flower: Fix chain template offload

When a qdisc is deleted from a net device the stack instructs the underlying driver to remove its flow offload callback from the associated filter block using the 'FLOW_BLOCK_UNBIND' command. The stack then continues to replay the removal of the filters in the block for this driver by iterating over the chains in the block and invoking the 'reoffload' operation of the classifier being used. In turn, the classifier in its 'reoffload' operation prepares and emits a 'FLOW_CLS_DESTROY' command for each filter.

However, the stack does not do the same for chain templates and the underlying driver never receives a 'FLOW_CLS_TMPLT_DESTROY' command when a qdisc is deleted. This results in a memory leak [1] which can be reproduced using [2].

Fix by introducing a 'tmplt_reoffload' operation and have the stack invoke it with the appropriate arguments as part of the replay. Implement the operation in the sole classifier that supports chain templates (flower) by emitting the 'FLOW_CLS_TMPLT_{CREATE,DESTROY}' command based on whether a flow offload callback is being bound to a filter block or being unbound from one.

As far as I can tell, the issue happens since cited commit which reordered tcf_block_offload_unbind() before tcf_block_flush_all_chains() in __tcf_block_put(). The order cannot be reversed as the filter block is expected to be freed after flushing all the chains.

[1] unreferenced object 0xffff888107e28800 (size 2048): comm "tc", pid 1079, jiffies 4294958525 (age 3074.287s) hex dump (first 32 bytes): b1 a6 7c 11 81 88 ff ff e0 5b b3 10 81 88 ff ff ..|......[...... 01 00 00 00 00 00 00 00 e0 aa b0 84 ff ff ff ff ................ backtrace: [<ffffffff81c06a68>] __kmem_cache_alloc_node+0x1e8/0x320 [<ffffffff81ab374e>] __kmalloc+0x4e/0x90 [<ffffffff832aec6d>] mlxsw_sp_acl_ruleset_get+0x34d/0x7a0 [<ffffffff832bc195>] mlxsw_sp_flower_tmplt_create+0x145/0x180 [<ffffffff832b2e1a>] mlxsw_sp_flow_block_cb+0x1ea/0x280 [<ffffffff83a10613>] tc_setup_cb_call+0x183/0x340 [<ffffffff83a9f85a>] fl_tmplt_create+0x3da/0x4c0 [<ffffffff83a22435>] tc_ctl_chain+0xa15/0x1170 [<ffffffff838a863c>] rtnetlink_rcv_msg+0x3cc/0xed0 [<ffffffff83ac87f0>] netlink_rcv_skb+0x170/0x440 [<ffffffff83ac6270>] netlink_unicast+0x540/0x820 [<ffffffff83ac6e28>] netlink_sendmsg+0x8d8/0xda0 [<ffffffff83793def>] ____sys_sendmsg+0x30f/0xa80 [<ffffffff8379d29a>] ___sys_sendmsg+0x13a/0x1e0 [<ffffffff8379d50c>] __sys_sendmsg+0x11c/0x1f0 [<ffffffff843b9ce0>] do_syscall_64+0x40/0xe0 unreferenced object 0xffff88816d2c0400 (size 1024): comm "tc", pid 1079, jiffies 4294958525 (age 3074.287s) hex dump (first 32 bytes): 40 00 00 00 00 00 00 00 57 f6 38 be 00 00 00 00 @.......W.8..... 10 04 2c 6d 81 88 ff ff 10 04 2c 6d 81 88 ff ff ..,m......,m.... backtrace: [<ffffffff81c06a68>] __kmem_cache_alloc_node+0x1e8/0x320 [<ffffffff81ab36c1>] __kmalloc_node+0x51/0x90 [<ffffffff81a8ed96>] kvmalloc_node+0xa6/0x1f0 [<ffffffff82827d03>] bucket_table_alloc.isra.0+0x83/0x460 [<ffffffff82828d2b>] rhashtable_init+0x43b/0x7c0 [<ffffffff832aed48>] mlxsw_sp_acl_ruleset_get+0x428/0x7a0 [<ffffffff832bc195>] mlxsw_sp_flower_tmplt_create+0x145/0x180 [<ffffffff832b2e1a>] mlxsw_sp_flow_block_cb+0x1ea/0x280 [<ffffffff83a10613>] tc_setup_cb_call+0x183/0x340 [<ffffffff83a9f85a>] fl_tmplt_create+0x3da/0x4c0 [<ffffffff83a22435>] tc_ctl_chain+0xa15/0x1170 [<ffffffff838a863c>] rtnetlink_rcv_msg+0x3cc/0xed0 [<ffffffff83ac87f0>] netlink_rcv_skb+0x170/0x440 [<ffffffff83ac6270>] netlink_unicast+0x540/0x820 [<ffffffff83ac6e28>] netlink_sendmsg+0x8d8/0xda0 [<ffffffff83793def>] ____sys_sendmsg+0x30f/0xa80

[2] # tc qdisc add dev swp1 clsact # tc chain add dev swp1 ingress proto ip chain 1 flower dst_ip 0.0.0.0/32 # tc qdisc del dev ---truncated---

Weakness: CWE-787

Which versions are affected by CVE-2024-26669?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2024-26669?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2024-26669 being exploited?

There is no known exploitation of CVE-2024-26669 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-58750, BELL-CVE-2024-26669, DEBIAN-CVE-2024-26669, GHSA-2wjh-rvr2-xxjw, ROOT-OS-DEBIAN-11-CVE-2024-26669, ROOT-OS-DEBIAN-12-CVE-2024-26669 and 1 more.