diff -up openssh-7.4p1/pam_ssh_agent_auth-0.10.3/iterate_ssh_agent_keys.c.psaa-build openssh-7.4p1/pam_ssh_agent_auth-0.10.3/iterate_ssh_agent_keys.c

--- openssh-7.4p1/pam_ssh_agent_auth-0.10.3/iterate_ssh_agent_keys.c.psaa-build	2016-11-13 04:24:32.000000000 +0100

+++ openssh-7.4p1/pam_ssh_agent_auth-0.10.3/iterate_ssh_agent_keys.c	2017-02-13 16:06:17.468680048 +0100

@@ -39,6 +39,15 @@

 #include "buffer.h"

 #include "key.h"

 #include "authfd.h"

+#include "ssh.h"

+#include <sys/types.h>

+#include <sys/stat.h>

+#include <sys/socket.h>

+#include <sys/un.h>

+#include <unistd.h>

+#include <stdlib.h>

+#include <errno.h>

+#include <fcntl.h>

 #include <stdio.h>

 #include <openssl/evp.h>

 #include "ssh2.h"

@@ -176,6 +185,96 @@ pamsshagentauth_session_id2_gen(Buffer *

     return;

 }

+/* 

+ * Added by Jamie Beverly, ensure socket fd points to a socket owned by the user 

+ * A cursory check is done, but to avoid race conditions, it is necessary 

+ * to drop effective UID when connecting to the socket. 

+ *

+ * If the cause of error is EACCES, because we verified we would not have that 

+ * problem initially, we can safely assume that somebody is attempting to find a 

+ * race condition; so a more "direct" log message is generated.

+ */

+

+int

+ssh_get_authentication_socket_for_uid(uid_t uid)

+{

+	const char *authsocket;

+	int sock;

+	struct sockaddr_un sunaddr;

+	struct stat sock_st;

+

+	authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME);

+	if (!authsocket)

+		return -1;

+

+	/* Advisory only; seteuid ensures no race condition; but will only log if we see EACCES */

+	if( stat(authsocket,&sock_st) == 0) {

+		if(uid != 0 && sock_st.st_uid != uid) {

+			fatal("uid %lu attempted to open an agent socket owned by uid %lu", (unsigned long) uid, (unsigned long) sock_st.st_uid);

+			return -1;

+		}

+	}

+

+	/* 

+	 * Ensures that the EACCES tested for below can _only_ happen if somebody 

+	 * is attempting to race the stat above to bypass authentication.

+	 */

+	if( (sock_st.st_mode & S_IWUSR) != S_IWUSR || (sock_st.st_mode & S_IRUSR) != S_IRUSR) {

+		error("ssh-agent socket has incorrect permissions for owner");

+		return -1;

+	}

+

+	sunaddr.sun_family = AF_UNIX;

+	strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path));

+

+	sock = socket(AF_UNIX, SOCK_STREAM, 0);

+	if (sock < 0)

+		return -1;

+

+	/* close on exec */

+	if (fcntl(sock, F_SETFD, 1) == -1) {

+		close(sock);

+		return -1;

+	}

+

+	errno = 0; 

+	seteuid(uid); /* To ensure a race condition is not used to circumvent the stat

+	             above, we will temporarily drop UID to the caller */

+	if (connect(sock, (struct sockaddr *)&sunaddr, sizeof sunaddr) < 0) {

+		close(sock);

+        if(errno == EACCES)

+		fatal("MAJOR SECURITY WARNING: uid %lu made a deliberate and malicious attempt to open an agent socket owned by another user", (unsigned long) uid);

+		return -1;

+	}

+

+	seteuid(0); /* we now continue the regularly scheduled programming */

+

+	return sock;

+}

+

+AuthenticationConnection *

+ssh_get_authentication_connection_for_uid(uid_t uid)

+{

+	AuthenticationConnection *auth;

+	int sock;

+

+	sock = ssh_get_authentication_socket_for_uid(uid);

+

+	/*

+	 * Fail if we couldn't obtain a connection.  This happens if we

+	 * exited due to a timeout.

+	 */

+	if (sock < 0)

+		return NULL;

+

+	auth = xmalloc(sizeof(*auth));

+	auth->fd = sock;

+	buffer_init(&auth->identities);

+	auth->howmany = 0;

+

+	return auth;

+}

+

 int

 pamsshagentauth_find_authorized_keys(const char * user, const char * ruser, const char * servicename)

 {

@@ -190,7 +289,7 @@ pamsshagentauth_find_authorized_keys(con

     OpenSSL_add_all_digests();

     pamsshagentauth_session_id2_gen(&session_id2, user, ruser, servicename);

-    if ((ac = ssh_get_authentication_connection(uid))) {

+    if ((ac = ssh_get_authentication_connection_for_uid(uid))) {

         pamsshagentauth_verbose("Contacted ssh-agent of user %s (%u)", ruser, uid);

         for (key = ssh_get_first_identity(ac, &comment, 2); key != NULL; key = ssh_get_next_identity(ac, &comment, 2)) 

         {

@@ -219,3 +318,4 @@ pamsshagentauth_find_authorized_keys(con

     EVP_cleanup();

     return retval;

 }

+

diff -up openssh-7.4p1/pam_ssh_agent_auth-0.10.3/Makefile.in.psaa-build openssh-7.4p1/pam_ssh_agent_auth-0.10.3/Makefile.in

--- openssh-7.4p1/pam_ssh_agent_auth-0.10.3/Makefile.in.psaa-build	2016-11-13 04:24:32.000000000 +0100

+++ openssh-7.4p1/pam_ssh_agent_auth-0.10.3/Makefile.in	2017-02-13 16:04:58.685753236 +0100

@@ -52,7 +52,7 @@ PATHS=

 CC=@CC@

 LD=@LD@

 CFLAGS=@CFLAGS@

-CPPFLAGS=-I. -I$(srcdir) @CPPFLAGS@ $(PATHS) @DEFS@

+CPPFLAGS=-I.. -I$(srcdir) -I/usr/include/nss3 -I/usr/include/nspr4 @CPPFLAGS@ $(PATHS) @DEFS@

 LIBS=@LIBS@

 AR=@AR@

 AWK=@AWK@

@@ -61,7 +61,7 @@ INSTALL=@INSTALL@

 PERL=@PERL@

 SED=@SED@

 ENT=@ENT@

-LDFLAGS=-L. -Lopenbsd-compat/ @LDFLAGS@

+LDFLAGS=-L.. -L../openbsd-compat/ @LDFLAGS@

 LDFLAGS_SHARED = @LDFLAGS_SHARED@

 EXEEXT=@EXEEXT@

@@ -74,7 +74,7 @@ SSHOBJS=xmalloc.o atomicio.o authfd.o bu

 ED25519OBJS=ed25519-donna/ed25519.o

-PAM_SSH_AGENT_AUTH_OBJS=pam_user_key_allowed2.o iterate_ssh_agent_keys.o userauth_pubkey_from_id.o pam_user_authorized_keys.o get_command_line.o

+PAM_SSH_AGENT_AUTH_OBJS=pam_user_key_allowed2.o iterate_ssh_agent_keys.o userauth_pubkey_from_id.o pam_user_authorized_keys.o get_command_line.o secure_filename.o

 MANPAGES_IN	= pam_ssh_agent_auth.pod

@@ -94,13 +94,13 @@ $(PAM_MODULES): Makefile.in config.h

 .c.o:

 	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@

-LIBCOMPAT=openbsd-compat/libopenbsd-compat.a

+LIBCOMPAT=../openbsd-compat/libopenbsd-compat.a

 $(LIBCOMPAT): always

 	(cd openbsd-compat && $(MAKE))

 always:

-pam_ssh_agent_auth.so: $(LIBCOMPAT) $(SSHOBJS) $(ED25519OBJS) $(PAM_SSH_AGENT_AUTH_OBJS)  pam_ssh_agent_auth.o

-	$(LD) $(LDFLAGS_SHARED) -o $@ $(SSHOBJS) $(ED25519OBJS) $(PAM_SSH_AGENT_AUTH_OBJS) $(LDFLAGS) -lopenbsd-compat pam_ssh_agent_auth.o $(LIBS) -lpam

+pam_ssh_agent_auth.so: $(PAM_SSH_AGENT_AUTH_OBJS)  pam_ssh_agent_auth.o

+	$(LD) $(LDFLAGS_SHARED) -o $@ $(PAM_SSH_AGENT_AUTH_OBJS) $(LDFLAGS) -lssh -lopenbsd-compat pam_ssh_agent_auth.o $(LIBS) -lpam -lnss3

 $(MANPAGES): $(MANPAGES_IN)

 	pod2man --section=8 --release=v0.10.3 --name=pam_ssh_agent_auth --official --center "PAM" pam_ssh_agent_auth.pod > pam_ssh_agent_auth.8