CVE-2026-74748netfilter: ipset: fix refcount race between list:set GC and swap

Official description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ipset: fix refcount race between list:set GC and swap __ip_set_put_byindex() resolved the index to a set pointer under RCU, then took ip_set_ref_lock in __ip_set_put() to decrement set->ref. ip_set_swap() holds that same lock while swapping both the ip_set_list slots and the two sets' ref counters, so it can interleave between the dereference and the lock acquisition, leaving the caller to decrement a set whose reference already moved to the other index and hit BUG_ON(set->ref == 0). list_set_gc() reaches this from timer softirq, which the nfnl mutex does not serialize against swap: an expiring list:set member calls list_set_del() -> ip_set_put_byindex() while IPSET_CMD_SWAP runs on the referenced sets. Resolve the index and decrement under ip_set_ref_lock, as ip_set_swap() already does, keeping the refcount tied to the index rather than to a stale set pointer. kernel BUG at net/netfilter/ipset/ip_set_core.c:685! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:ip_set_put_byindex (net/netfilter/ipset/ip_set_core.c:870) Call Trace: <IRQ> list_set_del (net/netfilter/ipset/ip_set_list_set.c:159) set_cleanup_entries (net/netfilter/ipset/ip_set_list_set.c:181) list_set_gc (net/netfilter/ipset/ip_set_list_set.c:578) call_timer_fn (kernel/time/timer.c:1748) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2374) run_timer_softirq (kernel/time/timer.c:2405) </IRQ> Kernel panic - not syncing: Fatal exception in interrupt

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/97a01de0c6321b7210d30d0a4d60f10f561097c7
• https://git.kernel.org/stable/c/c21afc7c216a4d257a4f3f300e0791890bc846b9
• https://git.kernel.org/stable/c/b0aab9dd1a348b99d75ff52765719d0cc2050630
• https://git.kernel.org/stable/c/b891e7a6bb06e0f6560e5932665ac660acd12225
• https://git.kernel.org/stable/c/20cb13a523f0a05cb2d0a7d72abae687683712e0
• https://git.kernel.org/stable/c/cb20da33839f28f590c99f16bafaa6151451c0e8
• https://git.kernel.org/stable/c/24ffcb1e1688c55fd2a505f064295cd28eac546d
• https://git.kernel.org/stable/c/0c88868271653537ed443272dd8e7d13634d214b