This is a note to let you know that I've just added the patch titled af_unix: fix races in sk_peer_pid and sk_peer_cred accesses to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: af_unix-fix-races-in-sk_peer_pid-and-sk_peer_cred-accesses.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 35306eb23814444bd4021f8a1c3047d3cb0c8b2b Mon Sep 17 00:00:00 2001 From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Wed, 29 Sep 2021 15:57:50 -0700 Subject: af_unix: fix races in sk_peer_pid and sk_peer_cred accesses From: Eric Dumazet <edumazet@xxxxxxxxxx> commit 35306eb23814444bd4021f8a1c3047d3cb0c8b2b upstream. Jann Horn reported that SO_PEERCRED and SO_PEERGROUPS implementations are racy, as af_unix can concurrently change sk_peer_pid and sk_peer_cred. In order to fix this issue, this patch adds a new spinlock that needs to be used whenever these fields are read or written. Jann also pointed out that l2cap_sock_get_peer_pid_cb() is currently reading sk->sk_peer_pid which makes no sense, as this field is only possibly set by AF_UNIX sockets. We will have to clean this in a separate patch. This could be done by reverting b48596d1dc25 "Bluetooth: L2CAP: Add get_peer_pid callback" or implementing what was truly expected. Fixes: 109f6e39fa07 ("af_unix: Allow SO_PEERCRED to work across namespaces.") Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Reported-by: Jann Horn <jannh@xxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Cc: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> [backport note: 4.4 and 4.9 don't have SO_PEERGROUPS, only SO_PEERCRED] [backport note: got rid of sk_get_peer_cred(), no users in 4.4/4.9] Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/net/sock.h | 2 ++ net/core/sock.c | 12 +++++++++--- net/unix/af_unix.c | 34 ++++++++++++++++++++++++++++------ 3 files changed, 39 insertions(+), 9 deletions(-) --- a/include/net/sock.h +++ b/include/net/sock.h @@ -429,8 +429,10 @@ struct sock { #if IS_ENABLED(CONFIG_CGROUP_NET_PRIO) __u32 sk_cgrp_prioidx; #endif + spinlock_t sk_peer_lock; struct pid *sk_peer_pid; const struct cred *sk_peer_cred; + long sk_rcvtimeo; long sk_sndtimeo; struct timer_list sk_timer; --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1014,7 +1014,6 @@ set_rcvbuf: } EXPORT_SYMBOL(sock_setsockopt); - static void cred_to_ucred(struct pid *pid, const struct cred *cred, struct ucred *ucred) { @@ -1174,7 +1173,11 @@ int sock_getsockopt(struct socket *sock, struct ucred peercred; if (len > sizeof(peercred)) len = sizeof(peercred); + + spin_lock(&sk->sk_peer_lock); cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred, &peercred); + spin_unlock(&sk->sk_peer_lock); + if (copy_to_user(optval, &peercred, len)) return -EFAULT; goto lenout; @@ -1467,9 +1470,10 @@ void sk_destruct(struct sock *sk) sk->sk_frag.page = NULL; } - if (sk->sk_peer_cred) - put_cred(sk->sk_peer_cred); + /* We do not need to acquire sk->sk_peer_lock, we are the last user. */ + put_cred(sk->sk_peer_cred); put_pid(sk->sk_peer_pid); + if (likely(sk->sk_net_refcnt)) put_net(sock_net(sk)); sk_prot_free(sk->sk_prot_creator, sk); @@ -2442,6 +2446,8 @@ void sock_init_data(struct socket *sock, sk->sk_peer_pid = NULL; sk->sk_peer_cred = NULL; + spin_lock_init(&sk->sk_peer_lock); + sk->sk_write_pending = 0; sk->sk_rcvlowat = 1; sk->sk_rcvtimeo = MAX_SCHEDULE_TIMEOUT; --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -594,20 +594,42 @@ static void unix_release_sock(struct soc static void init_peercred(struct sock *sk) { - put_pid(sk->sk_peer_pid); - if (sk->sk_peer_cred) - put_cred(sk->sk_peer_cred); + const struct cred *old_cred; + struct pid *old_pid; + + spin_lock(&sk->sk_peer_lock); + old_pid = sk->sk_peer_pid; + old_cred = sk->sk_peer_cred; sk->sk_peer_pid = get_pid(task_tgid(current)); sk->sk_peer_cred = get_current_cred(); + spin_unlock(&sk->sk_peer_lock); + + put_pid(old_pid); + put_cred(old_cred); } static void copy_peercred(struct sock *sk, struct sock *peersk) { - put_pid(sk->sk_peer_pid); - if (sk->sk_peer_cred) - put_cred(sk->sk_peer_cred); + const struct cred *old_cred; + struct pid *old_pid; + + if (sk < peersk) { + spin_lock(&sk->sk_peer_lock); + spin_lock_nested(&peersk->sk_peer_lock, SINGLE_DEPTH_NESTING); + } else { + spin_lock(&peersk->sk_peer_lock); + spin_lock_nested(&sk->sk_peer_lock, SINGLE_DEPTH_NESTING); + } + old_pid = sk->sk_peer_pid; + old_cred = sk->sk_peer_cred; sk->sk_peer_pid = get_pid(peersk->sk_peer_pid); sk->sk_peer_cred = get_cred(peersk->sk_peer_cred); + + spin_unlock(&sk->sk_peer_lock); + spin_unlock(&peersk->sk_peer_lock); + + put_pid(old_pid); + put_cred(old_cred); } static int unix_listen(struct socket *sock, int backlog) Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-4.4/af_unix-fix-races-in-sk_peer_pid-and-sk_peer_cred-accesses.patch