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af_unix: fix races in sk_peer_pid and sk_peer_cred accesses 

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 b48596d1dc "Bluetooth: L2CAP: Add get_peer_pid callback"
or implementing what was truly expected.

Fixes: 109f6e39fa ("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>
This commit is contained in:
Eric Dumazet 2021-09-29 15:57:50 -07:00 committed by David S. Miller
parent 656ed8b015
commit 35306eb238
3 changed files with 56 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/sock.h
View File

@ -488,8 +488,10 @@ struct sock {
u8 sk_prefer_busy_poll;
u16 sk_busy_poll_budget;
#endif
spinlock_t sk_peer_lock;
struct pid *sk_peer_pid;
const struct cred *sk_peer_cred;
long sk_rcvtimeo;
ktime_t sk_stamp;
#if BITS_PER_LONG==32

32
net/core/sock.c
View File

@ -1376,6 +1376,16 @@ set_sndbuf:
}
EXPORT_SYMBOL(sock_setsockopt);
static const struct cred *sk_get_peer_cred(struct sock *sk)
{
const struct cred *cred;
spin_lock(&sk->sk_peer_lock);
cred = get_cred(sk->sk_peer_cred);
spin_unlock(&sk->sk_peer_lock);
return cred;
}
static void cred_to_ucred(struct pid *pid, const struct cred *cred,
struct ucred *ucred)
@ -1552,7 +1562,11 @@ 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;
@ -1560,20 +1574,23 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
case SO_PEERGROUPS:
{
const struct cred *cred;
int ret, n;
if (!sk->sk_peer_cred)
cred = sk_get_peer_cred(sk);
if (!cred)
return -ENODATA;
n = sk->sk_peer_cred->group_info->ngroups;
n = cred->group_info->ngroups;
if (len < n * sizeof(gid_t)) {
len = n * sizeof(gid_t);
put_cred(cred);
return put_user(len, optlen) ? -EFAULT : -ERANGE;
}
len = n * sizeof(gid_t);
ret = groups_to_user((gid_t __user *)optval,
sk->sk_peer_cred->group_info);
ret = groups_to_user((gid_t __user *)optval, cred->group_info);
put_cred(cred);
if (ret)
return ret;
goto lenout;
@ -1935,9 +1952,10 @@ 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);
@ -3145,6 +3163,8 @@ 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

@ -608,20 +608,42 @@ 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)