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authorEric Dumazet <edumazet@google.com>2021-09-30 01:57:50 +0300
committerDavid S. Miller <davem@davemloft.net>2021-09-30 16:18:40 +0300
commit35306eb23814444bd4021f8a1c3047d3cb0c8b2b (patch)
treef01ff49d4c08b6e5465f1ad535264518d1885bdc
parent656ed8b015f19bf3f6e6b3ddd9a4bb4aa5ca73e1 (diff)
downloadlinux-35306eb23814444bd4021f8a1c3047d3cb0c8b2b.tar.xz
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 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>
-rw-r--r--include/net/sock.h2
-rw-r--r--net/core/sock.c32
-rw-r--r--net/unix/af_unix.c34
3 files changed, 56 insertions, 12 deletions
diff --git a/include/net/sock.h b/include/net/sock.h
index dc3f8169312e..ae929e21a376 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -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
diff --git a/net/core/sock.c b/net/core/sock.c
index 7060d183216e..c1601f75ec4b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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;
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index f505b89bda6a..efac5989edb5 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -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)