On Tue, Apr 14, 2026 at 7:13 AM Michal Luczaj <[email protected]> wrote: > > When a BPF iterator program updates a sockmap, there is a race condition in > unix_stream_bpf_update_proto() where the `peer` pointer can become stale[1] > during a state transition TCP_ESTABLISHED -> TCP_CLOSE. > > CPU0 bpf CPU1 close > -------- ---------- > // unix_stream_bpf_update_proto() > sk_pair = unix_peer(sk) > if (unlikely(!sk_pair)) > return -EINVAL; > // unix_release_sock() > skpair = unix_peer(sk); > unix_peer(sk) = NULL; > sock_put(skpair) > sock_hold(sk_pair) // UaF > > More practically, this fix guarantees that the iterator program is > consistently provided with a unix socket that remains stable during > iterator execution. > > [1]: > BUG: KASAN: slab-use-after-free in unix_stream_bpf_update_proto+0x155/0x490 > Write of size 4 at addr ffff8881178c9a00 by task test_progs/2231 > Call Trace: > dump_stack_lvl+0x5d/0x80 > print_report+0x170/0x4f3 > kasan_report+0xe4/0x1c0 > kasan_check_range+0x125/0x200 > unix_stream_bpf_update_proto+0x155/0x490 > sock_map_link+0x71c/0xec0 > sock_map_update_common+0xbc/0x600 > sock_map_update_elem+0x19a/0x1f0 > bpf_prog_bbbf56096cdd4f01_selective_dump_unix+0x20c/0x217 > bpf_iter_run_prog+0x21e/0xae0 > bpf_iter_unix_seq_show+0x1e0/0x2a0 > bpf_seq_read+0x42c/0x10d0 > vfs_read+0x171/0xb20 > ksys_read+0xff/0x200 > do_syscall_64+0xf7/0x5e0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Allocated by task 2236: > kasan_save_stack+0x30/0x50 > kasan_save_track+0x14/0x30 > __kasan_slab_alloc+0x63/0x80 > kmem_cache_alloc_noprof+0x1d5/0x680 > sk_prot_alloc+0x59/0x210 > sk_alloc+0x34/0x470 > unix_create1+0x86/0x8a0 > unix_stream_connect+0x318/0x15b0 > __sys_connect+0xfd/0x130 > __x64_sys_connect+0x72/0xd0 > do_syscall_64+0xf7/0x5e0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Freed by task 2236: > kasan_save_stack+0x30/0x50 > kasan_save_track+0x14/0x30 > kasan_save_free_info+0x3b/0x70 > __kasan_slab_free+0x47/0x70 > kmem_cache_free+0x11c/0x590 > __sk_destruct+0x432/0x6e0 > unix_release_sock+0x9b3/0xf60 > unix_release+0x8a/0xf0 > __sock_release+0xb0/0x270 > sock_close+0x18/0x20 > __fput+0x36e/0xac0 > fput_close_sync+0xe5/0x1a0 > __x64_sys_close+0x7d/0xd0 > do_syscall_64+0xf7/0x5e0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Suggested-by: Kuniyuki Iwashima <[email protected]> > Fixes: 2c860a43dd77 ("bpf: af_unix: Implement BPF iterator for UNIX domain > socket.") > Signed-off-by: Michal Luczaj <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]> Thanks for the fixes, Michal !
