7.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Luczaj <redacted>

[ Upstream commit 64c2f93fc3254d3bf5de4445fb732ee5c451edb6 ]

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

Fixes: 2c860a43dd77 ("bpf: af_unix: Implement BPF iterator for UNIX domain socket.")
Suggested-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Michal Luczaj <redacted>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260414-unix-proto-update-null-ptr-deref-v4-5-2af6fe97918e@rbox.co
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/unix/af_unix.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index b1ec96512bf72..660c7c441e0db 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c

@@ -3740,6 +3740,7 @@ static int bpf_iter_unix_seq_show(struct seq_file *seq, void *v)
 		return 0;
 
 	lock_sock(sk);
+	unix_state_lock(sk);
 
 	if (unlikely(sock_flag(sk, SOCK_DEAD))) {
 		ret = SEQ_SKIP;

@@ -3751,6 +3752,7 @@ static int bpf_iter_unix_seq_show(struct seq_file *seq, void *v)
 	prog = bpf_iter_get_info(&meta, false);
 	ret = unix_prog_seq_show(prog, &meta, v, uid);
 unlock:
+	unix_state_unlock(sk);
 	release_sock(sk);
 	return ret;
 }

-- 
2.53.0