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af_unix: fix races in sk_peer_pid and sk_peer_cred accesses

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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@google.com>
Reported-by: Jann Horn <jannh@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[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@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric Dumazet 2021-09-29 15:57:50 -07:00 committed by Greg Kroah-Hartman
parent af222b7cde
commit 09818f629b
3 changed files with 39 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/sock.h
View File

@ -420,8 +420,10 @@ struct sock {
u32 sk_max_ack_backlog;
__u32 sk_priority;
__u32 sk_mark;
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;

12
net/core/sock.c
View File

@ -1011,7 +1011,6 @@ set_rcvbuf:
}
EXPORT_SYMBOL(sock_setsockopt);
static void cred_to_ucred(struct pid *pid, const struct cred *cred,
struct ucred *ucred)
{
@ -1171,7 +1170,11 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
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;
@ -1439,9 +1442,10 @@ static void __sk_destruct(struct rcu_head *head)
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);
@ -2490,6 +2494,8 @@ void sock_init_data(struct socket *sock, struct sock *sk)
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;

34
net/unix/af_unix.c
View File

@ -594,20 +594,42 @@ static void unix_release_sock(struct sock *sk, int embrion)
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)