6.9-stable review patch. If anyone has any objections, please let me know.
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From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 51d1b25a720982324871338b1a36b197ec9bd6f0 ]
syzkaller reported data-race of sk->sk_hash in unix_autobind() [0], and the same ones exist in unix_bind_bsd() and unix_bind_abstract().
The three bind() functions prefetch sk->sk_hash locklessly and use it later after validating that unix_sk(sk)->addr is NULL under unix_sk(sk)->bindlock.
The prefetched sk->sk_hash is the hash value of unbound socket set in unix_create1() and does not change until bind() completes.
There could be a chance that sk->sk_hash changes after the lockless read. However, in such a case, non-NULL unix_sk(sk)->addr is visible under unix_sk(sk)->bindlock, and bind() returns -EINVAL without using the prefetched value.
The KCSAN splat is false-positive, but let's silence it by reading sk->sk_hash under unix_sk(sk)->bindlock.
[0]: BUG: KCSAN: data-race in unix_autobind / unix_autobind
write to 0xffff888034a9fb88 of 4 bytes by task 4468 on cpu 0: __unix_set_addr_hash net/unix/af_unix.c:331 [inline] unix_autobind+0x47a/0x7d0 net/unix/af_unix.c:1185 unix_dgram_connect+0x7e3/0x890 net/unix/af_unix.c:1373 __sys_connect_file+0xd7/0xe0 net/socket.c:2048 __sys_connect+0x114/0x140 net/socket.c:2065 __do_sys_connect net/socket.c:2075 [inline] __se_sys_connect net/socket.c:2072 [inline] __x64_sys_connect+0x40/0x50 net/socket.c:2072 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x4f/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x46/0x4e
read to 0xffff888034a9fb88 of 4 bytes by task 4465 on cpu 1: unix_autobind+0x28/0x7d0 net/unix/af_unix.c:1134 unix_dgram_connect+0x7e3/0x890 net/unix/af_unix.c:1373 __sys_connect_file+0xd7/0xe0 net/socket.c:2048 __sys_connect+0x114/0x140 net/socket.c:2065 __do_sys_connect net/socket.c:2075 [inline] __se_sys_connect net/socket.c:2072 [inline] __x64_sys_connect+0x40/0x50 net/socket.c:2072 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x4f/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x46/0x4e
value changed: 0x000000e4 -> 0x000001e3
Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 4465 Comm: syz-executor.0 Not tainted 6.8.0-12822-gcd51db110a7e #12 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Fixes: afd20b9290e1 ("af_unix: Replace the big lock with small locks.") Reported-by: syzkaller syzkaller@googlegroups.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Link: https://lore.kernel.org/r/20240522154218.78088-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/unix/af_unix.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 6498e41e2ecf9..439c531744a27 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1131,8 +1131,8 @@ static struct sock *unix_find_other(struct net *net,
static int unix_autobind(struct sock *sk) { - unsigned int new_hash, old_hash = sk->sk_hash; struct unix_sock *u = unix_sk(sk); + unsigned int new_hash, old_hash; struct net *net = sock_net(sk); struct unix_address *addr; u32 lastnum, ordernum; @@ -1155,6 +1155,7 @@ static int unix_autobind(struct sock *sk) addr->name->sun_family = AF_UNIX; refcount_set(&addr->refcnt, 1);
+ old_hash = sk->sk_hash; ordernum = get_random_u32(); lastnum = ordernum & 0xFFFFF; retry: @@ -1195,8 +1196,8 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr, { umode_t mode = S_IFSOCK | (SOCK_INODE(sk->sk_socket)->i_mode & ~current_umask()); - unsigned int new_hash, old_hash = sk->sk_hash; struct unix_sock *u = unix_sk(sk); + unsigned int new_hash, old_hash; struct net *net = sock_net(sk); struct mnt_idmap *idmap; struct unix_address *addr; @@ -1234,6 +1235,7 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr, if (u->addr) goto out_unlock;
+ old_hash = sk->sk_hash; new_hash = unix_bsd_hash(d_backing_inode(dentry)); unix_table_double_lock(net, old_hash, new_hash); u->path.mnt = mntget(parent.mnt); @@ -1261,8 +1263,8 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr, static int unix_bind_abstract(struct sock *sk, struct sockaddr_un *sunaddr, int addr_len) { - unsigned int new_hash, old_hash = sk->sk_hash; struct unix_sock *u = unix_sk(sk); + unsigned int new_hash, old_hash; struct net *net = sock_net(sk); struct unix_address *addr; int err; @@ -1280,6 +1282,7 @@ static int unix_bind_abstract(struct sock *sk, struct sockaddr_un *sunaddr, goto out_mutex; }
+ old_hash = sk->sk_hash; new_hash = unix_abstract_hash(addr->name, addr->len, sk->sk_type); unix_table_double_lock(net, old_hash, new_hash);