[PATCH 4.14 003/159] kcm: Check if sk_user_data already set in kcm_attach

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Tom Herbert 

commit e5571240236c5652f3e079b1d5866716a7ad819c upstream.

This is needed to prevent sk_user_data being overwritten.
The check is done under the callback lock. This should prevent
a socket from being attached twice to a KCM mux. It also prevents
a socket from being attached for other use cases of sk_user_data
as long as the other cases set sk_user_data under the lock.
Followup work is needed to unify all the use cases of sk_user_data
to use the same locking.

Reported-by: syzbot+114b15f2be420a888...@syzkaller.appspotmail.com
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Tom Herbert 
Reviewed-by: Eric Dumazet 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman 

---
 net/kcm/kcmsock.c |   16 ++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1405,9 +1405,18 @@ static int kcm_attach(struct socket *soc
return err;
}
 
-   sock_hold(csk);
-
write_lock_bh(>sk_callback_lock);
+
+   /* Check if sk_user_data is aready by KCM or someone else.
+* Must be done under lock to prevent race conditions.
+*/
+   if (csk->sk_user_data) {
+   write_unlock_bh(>sk_callback_lock);
+   strp_done(>strp);
+   kmem_cache_free(kcm_psockp, psock);
+   return -EALREADY;
+   }
+
psock->save_data_ready = csk->sk_data_ready;
psock->save_write_space = csk->sk_write_space;
psock->save_state_change = csk->sk_state_change;
@@ -1415,8 +1424,11 @@ static int kcm_attach(struct socket *soc
csk->sk_data_ready = psock_data_ready;
csk->sk_write_space = psock_write_space;
csk->sk_state_change = psock_state_change;
+
write_unlock_bh(>sk_callback_lock);
 
+   sock_hold(csk);
+
/* Finished initialization, now add the psock to the MUX. */
spin_lock_bh(>lock);
head = >psocks;

[PATCH 4.14 003/159] kcm: Check if sk_user_data already set in kcm_attach

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Tom Herbert 

commit e5571240236c5652f3e079b1d5866716a7ad819c upstream.

This is needed to prevent sk_user_data being overwritten.
The check is done under the callback lock. This should prevent
a socket from being attached twice to a KCM mux. It also prevents
a socket from being attached for other use cases of sk_user_data
as long as the other cases set sk_user_data under the lock.
Followup work is needed to unify all the use cases of sk_user_data
to use the same locking.

Reported-by: syzbot+114b15f2be420a888...@syzkaller.appspotmail.com
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Tom Herbert 
Reviewed-by: Eric Dumazet 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman 

---
 net/kcm/kcmsock.c |   16 ++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1405,9 +1405,18 @@ static int kcm_attach(struct socket *soc
return err;
}
 
-   sock_hold(csk);
-
write_lock_bh(>sk_callback_lock);
+
+   /* Check if sk_user_data is aready by KCM or someone else.
+* Must be done under lock to prevent race conditions.
+*/
+   if (csk->sk_user_data) {
+   write_unlock_bh(>sk_callback_lock);
+   strp_done(>strp);
+   kmem_cache_free(kcm_psockp, psock);
+   return -EALREADY;
+   }
+
psock->save_data_ready = csk->sk_data_ready;
psock->save_write_space = csk->sk_write_space;
psock->save_state_change = csk->sk_state_change;
@@ -1415,8 +1424,11 @@ static int kcm_attach(struct socket *soc
csk->sk_data_ready = psock_data_ready;
csk->sk_write_space = psock_write_space;
csk->sk_state_change = psock_state_change;
+
write_unlock_bh(>sk_callback_lock);
 
+   sock_hold(csk);
+
/* Finished initialization, now add the psock to the MUX. */
spin_lock_bh(>lock);
head = >psocks;