CVE-2025-21959

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

netfilter: nf_conncount: Fully initialize struct nf_conncount_tuple in insert_tree()

Since commit b36e4523d4d5 ("netfilter: nf_conncount: fix garbage collection confirm race"), cpu and jiffies32 were introduced to the struct nf_conncount_tuple.

The commit made nf_conncount_add() initialize conn->cpu and conn->jiffies32 when allocating the struct. In contrast, count_tree() was not changed to initialize them.

By commit 34848d5c896e ("netfilter: nf_conncount: Split insert and traversal"), count_tree() was split and the relevant allocation code now resides in insert_tree(). Initialize conn->cpu and conn->jiffies32 in insert_tree().

BUG: KMSAN: uninit-value in find_or_evict net/netfilter/nf_conncount.c:117 [inline] BUG: KMSAN: uninit-value in __nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143 find_or_evict net/netfilter/nf_conncount.c:117 [inline] __nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143 count_tree net/netfilter/nf_conncount.c:438 [inline] nf_conncount_count+0x82f/0x1e80 net/netfilter/nf_conncount.c:521 connlimit_mt+0x7f6/0xbd0 net/netfilter/xt_connlimit.c:72 __nft_match_eval net/netfilter/nft_compat.c:403 [inline] nft_match_eval+0x1a5/0x300 net/netfilter/nft_compat.c:433 expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline] nft_do_chain+0x426/0x2290 net/netfilter/nf_tables_core.c:288 nft_do_chain_ipv4+0x1a5/0x230 net/netfilter/nft_chain_filter.c:23 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626 nf_hook_slow_list+0x24d/0x860 net/netfilter/core.c:663 NF_HOOK_LIST include/linux/netfilter.h:350 [inline] ip_sublist_rcv+0x17b7/0x17f0 net/ipv4/ip_input.c:633 ip_list_rcv+0x9ef/0xa40 net/ipv4/ip_input.c:669 __netif_receive_skb_list_ptype net/core/dev.c:5936 [inline] __netif_receive_skb_list_core+0x15c5/0x1670 net/core/dev.c:5983 __netif_receive_skb_list net/core/dev.c:6035 [inline] netif_receive_skb_list_internal+0x1085/0x1700 net/core/dev.c:6126 netif_receive_skb_list+0x5a/0x460 net/core/dev.c:6178 xdp_recv_frames net/bpf/test_run.c:280 [inline] xdp_test_run_batch net/bpf/test_run.c:361 [inline] bpf_test_run_xdp_live+0x2e86/0x3480 net/bpf/test_run.c:390 bpf_prog_test_run_xdp+0xf1d/0x1ae0 net/bpf/test_run.c:1316 bpf_prog_test_run+0x5e5/0xa30 kernel/bpf/syscall.c:4407 __sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5813 __do_sys_bpf kernel/bpf/syscall.c:5902 [inline] __se_sys_bpf kernel/bpf/syscall.c:5900 [inline] __ia32_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5900 ia32_sys_call+0x394d/0x4180 arch/x86/include/generated/asm/syscalls_32.h:358 do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline] __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/common.c:387 do_fast_syscall_32+0x38/0x80 arch/x86/entry/common.c:412 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:450 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Uninit was created at: slab_post_alloc_hook mm/slub.c:4121 [inline] slab_alloc_node mm/slub.c:4164 [inline] kmem_cache_alloc_noprof+0x915/0xe10 mm/slub.c:4171 insert_tree net/netfilter/nf_conncount.c:372 [inline] count_tree net/netfilter/nf_conncount.c:450 [inline] nf_conncount_count+0x1415/0x1e80 net/netfilter/nf_conncount.c:521 connlimit_mt+0x7f6/0xbd0 net/netfilter/xt_connlimit.c:72 __nft_match_eval net/netfilter/nft_compat.c:403 [inline] nft_match_eval+0x1a5/0x300 net/netfilter/nft_compat.c:433 expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline] nft_do_chain+0x426/0x2290 net/netfilter/nf_tables_core.c:288 nft_do_chain_ipv4+0x1a5/0x230 net/netfilter/nft_chain_filter.c:23 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626 nf_hook_slow_list+0x24d/0x860 net/netfilter/core.c:663 NF_HOOK_LIST include/linux/netfilter.h:350 [inline] ip_sublist_rcv+0x17b7/0x17f0 net/ipv4/ip_input.c:633 ip_list_rcv+0x9ef/0xa40 net/ip ---truncated---

This vulnerability is rated as having a Moderate impact for Red Hat Enterprise Linux because exploitation requires a local attacker or traffic processed by netfilter rules actively using the connlimit match, restricting the attack surface to environments with specific firewall configurations. An uninitialized memory read within the kernel connection counting mechanism can lead to system instability and denial of service, without directly exposing confidentiality or integrity. Default installations without connection-limiting packet filtering rules are not exposed to this issue during normal network operations.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.