net: fix incorrect credentials passing

[ Upstream commit 83f1b4b ]

Commit 257b535 ("scm: Capture the full credentials of the scm
sender") changed the credentials passing code to pass in the effective
uid/gid instead of the real uid/gid.

Obviously this doesn't matter most of the time (since normally they are
the same), but it results in differences for suid binaries when the wrong
uid/gid ends up being used.

This just undoes that (presumably unintentional) part of the commit.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/socket.h

@@ -316,7 +316,8 @@ struct ucred {
 /* IPX options */
 #define IPX_TYPE	1
 
-extern void cred_to_ucred(struct pid *pid, const struct cred *cred, struct ucred *ucred);
+extern void cred_to_ucred(struct pid *pid, const struct cred *cred, struct ucred *ucred,
+			  bool use_effective);
 
 extern int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 extern int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,

include/net/scm.h

@@ -50,7 +50,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
 {
 	scm->pid  = get_pid(pid);
 	scm->cred = cred ? get_cred(cred) : NULL;
-	cred_to_ucred(pid, cred, &scm->creds);
+	cred_to_ucred(pid, cred, &scm->creds, false);
 }
 
 static __inline__ void scm_destroy_cred(struct scm_cookie *scm)

net/core/sock.c

@@ -815,15 +815,20 @@ EXPORT_SYMBOL(sock_setsockopt);
 
 
 void cred_to_ucred(struct pid *pid, const struct cred *cred,
-		   struct ucred *ucred)
+		   struct ucred *ucred, bool use_effective)
 {
 	ucred->pid = pid_vnr(pid);
 	ucred->uid = ucred->gid = -1;
 	if (cred) {
 		struct user_namespace *current_ns = current_user_ns();
 
-		ucred->uid = user_ns_map_uid(current_ns, cred, cred->euid);
-		ucred->gid = user_ns_map_gid(current_ns, cred, cred->egid);
+		if (use_effective) {
+			ucred->uid = user_ns_map_uid(current_ns, cred, cred->euid);
+			ucred->gid = user_ns_map_gid(current_ns, cred, cred->egid);
+		} else {
+			ucred->uid = user_ns_map_uid(current_ns, cred, cred->uid);
+			ucred->gid = user_ns_map_gid(current_ns, cred, cred->gid);
+		}
 	}
 }
 EXPORT_SYMBOL_GPL(cred_to_ucred);
@@ -984,7 +989,8 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 		struct ucred peercred;
 		if (len > sizeof(peercred))
 			len = sizeof(peercred);
-		cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred, &peercred);
+		cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred,
+			      &peercred, true);
 		if (copy_to_user(optval, &peercred, len))
 			return -EFAULT;
 		goto lenout;