netfilter: nf_tables_offload: suppress WARN_ON_ONCE for ENOMEM in abort path

Summary

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables_offload: suppress WARN_ON_ONCE for ENOMEM in abort path In nft_flow_rule_offload_abort(), WARN_ON_ONCE(err) is triggered on every error during rollback, including -ENOMEM. Memory allocation failures are expected under low-memory conditions and do not indicate a kernel bug. Trace for example: nft_flow_offload_chain() // FLOW_BLOCK_BIND nft_flow_block_chain() nft_chain_offload_cmd() nft_block_offload_cmd() ->ndo_setup_tc() nsim_setup_tc() flow_block_cb_setup_simple() flow_block_cb_alloc() // fails to -ENOMEM The warning was reproduced on the 5.10 stable kernel under memory pressure via fault injection, but the underlying bug exists in mainline as well, as demonstrated by the ENOMEM trace above. The following splat was triggered during nf_tables transaction processing: WARNING: CPU: 0 PID: 8567 at net/netfilter/nf_tables_offload.c:532 nft_flow_rule_offload_abort net/netfilter/nf_tables_offload.c:532 [inline] WARNING: CPU: 0 PID: 8567 at net/netfilter/nf_tables_offload.c:532 nft_flow_rule_offload_commit+0x971/0xcd0 net/netfilter/nf_tables_offload.c:591 Modules linked in: CPU: 0 PID: 8567 Comm: syz-executor.0 Not tainted 5.10.260-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:nft_flow_rule_offload_abort net/netfilter/nf_tables_offload.c:532 [inline] RIP: 0010:nft_flow_rule_offload_commit+0x971/0xcd0 net/netfilter/nf_tables_offload.c:591 Call Trace: nf_tables_commit+0x3bd/0x4bd0 net/netfilter/nf_tables_api.c:8604 nfnetlink_rcv_batch+0xb1e/0x1f20 net/netfilter/nfnetlink.c:509 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:579 [inline] nfnetlink_rcv+0x3b3/0x420 net/netfilter/nfnetlink.c:597 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] netlink_unicast+0x6cd/0xa00 net/netfilter/af_netlink.c:1340 netlink_sendmsg+0x906/0xe10 net/netfilter/af_netlink.c:1919 sock_sendmsg_nosec net/socket.c:651 [inline] __sock_sendmsg+0x155/0x190 net/socket.c:663 ____sys_sendmsg+0x705/0x870 net/socket.c:2379 ___sys_sendmsg+0x100/0x170 net/socket.c:2433 __sys_sendmsg+0xe9/0x1c0 net/socket.c:2462 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1 Change the condition to WARN_ON_ONCE(err && err != -ENOMEM) so that warnings are only emitted for unexpected errors. This aligns with the common kernel practice of not warning on -ENOMEM. Found by Linux Verification Center (linuxtesting.org) with Syzkaller.