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From e89d4c97385ff8180e6e81e84c5aa745daf28a79 Mon Sep 17 00:00:00 2001
From: Thorsten Kukuk <kukuk@thkukuk.de>
Date: Mon, 22 Jun 2015 14:53:01 +0200
Subject: Release version 1.2.1
Security fix: CVE-2015-3238
If the process executing pam_sm_authenticate or pam_sm_chauthtok method
of pam_unix is not privileged enough to check the password, e.g.
if selinux is enabled, the _unix_run_helper_binary function is called.
When a long enough password is supplied (16 pages or more, i.e. 65536+
bytes on a system with 4K pages), this helper function hangs
indefinitely, blocked in the write(2) call while writing to a blocking
pipe that has a limited capacity.
With this fix, the verifiable password length will be limited to
PAM_MAX_RESP_SIZE bytes (i.e. 512 bytes) for pam_exec and pam_unix.
Index: pam/modules/pam_exec/pam_exec.8.xml
===================================================================
--- pam.orig/modules/pam_exec/pam_exec.8.xml
+++ pam/modules/pam_exec/pam_exec.8.xml
@@ -106,7 +106,8 @@
During authentication the calling command can read
the password from <citerefentry>
<refentrytitle>stdin</refentrytitle><manvolnum>3</manvolnum>
- </citerefentry>.
+ </citerefentry>. Only first <emphasis>PAM_MAX_RESP_SIZE</emphasis>
+ bytes of a password are provided to the command.
</para>
</listitem>
</varlistentry>
Index: pam/modules/pam_exec/pam_exec.c
===================================================================
--- pam.orig/modules/pam_exec/pam_exec.c
+++ pam/modules/pam_exec/pam_exec.c
@@ -178,11 +178,11 @@
}
pam_set_item (pamh, PAM_AUTHTOK, resp);
- authtok = strdupa (resp);
+ authtok = strndupa (resp, PAM_MAX_RESP_SIZE);
_pam_drop (resp);
}
else
- authtok = void_pass;
+ authtok = strndupa (void_pass, PAM_MAX_RESP_SIZE);
if (pipe(fds) != 0)
{
Index: pam/modules/pam_unix/pam_unix.8.xml
===================================================================
--- pam.orig/modules/pam_unix/pam_unix.8.xml
+++ pam/modules/pam_unix/pam_unix.8.xml
@@ -80,6 +80,13 @@
</para>
<para>
+ The maximum length of a password supported by the pam_unix module
+ via the helper binary is <emphasis>PAM_MAX_RESP_SIZE</emphasis>
+ - currently 512 bytes. The rest of the password provided by the
+ conversation function to the module will be ignored.
+ </para>
+
+ <para>
The password component of this module performs the task of updating
the user's password. The default encryption hash is taken from the
<emphasis remap='B'>ENCRYPT_METHOD</emphasis> variable from
Index: pam/modules/pam_unix/pam_unix_passwd.c
===================================================================
--- pam.orig/modules/pam_unix/pam_unix_passwd.c
+++ pam/modules/pam_unix/pam_unix_passwd.c
@@ -245,15 +245,22 @@
/* wait for child */
/* if the stored password is NULL */
int rc=0;
- if (fromwhat)
- pam_modutil_write(fds[1], fromwhat, strlen(fromwhat)+1);
- else
- pam_modutil_write(fds[1], "", 1);
- if (towhat) {
- pam_modutil_write(fds[1], towhat, strlen(towhat)+1);
+ if (fromwhat) {
+ int len = strlen(fromwhat);
+
+ if (len > PAM_MAX_RESP_SIZE)
+ len = PAM_MAX_RESP_SIZE;
+ pam_modutil_write(fds[1], fromwhat, len);
}
- else
- pam_modutil_write(fds[1], "", 1);
+ pam_modutil_write(fds[1], "", 1);
+ if (towhat) {
+ int len = strlen(towhat);
+
+ if (len > PAM_MAX_RESP_SIZE)
+ len = PAM_MAX_RESP_SIZE;
+ pam_modutil_write(fds[1], towhat, len);
+ }
+ pam_modutil_write(fds[1], "", 1);
close(fds[0]); /* close here to avoid possible SIGPIPE above */
close(fds[1]);
Index: pam/modules/pam_unix/passverify.c
===================================================================
--- pam.orig/modules/pam_unix/passverify.c
+++ pam/modules/pam_unix/passverify.c
@@ -1086,12 +1086,15 @@
int
read_passwords(int fd, int npass, char **passwords)
{
+ /* The passwords array must contain npass preallocated
+ * buffers of length MAXPASS + 1
+ */
int rbytes = 0;
int offset = 0;
int i = 0;
char *pptr;
while (npass > 0) {
- rbytes = read(fd, passwords[i]+offset, MAXPASS-offset);
+ rbytes = read(fd, passwords[i]+offset, MAXPASS+1-offset);
if (rbytes < 0) {
if (errno == EINTR) continue;
Index: pam/modules/pam_unix/passverify.h
===================================================================
--- pam.orig/modules/pam_unix/passverify.h
+++ pam/modules/pam_unix/passverify.h
@@ -8,7 +8,7 @@
#define PAM_UNIX_RUN_HELPER PAM_CRED_INSUFFICIENT
-#define MAXPASS 200 /* the maximum length of a password */
+#define MAXPASS PAM_MAX_RESP_SIZE /* the maximum length of a password */
#define OLD_PASSWORDS_FILE "/etc/security/opasswd"
Index: pam/modules/pam_unix/support.c
===================================================================
--- pam.orig/modules/pam_unix/support.c
+++ pam/modules/pam_unix/support.c
@@ -632,7 +632,12 @@
/* if the stored password is NULL */
int rc=0;
if (passwd != NULL) { /* send the password to the child */
- if (write(fds[1], passwd, strlen(passwd)+1) == -1) {
+ int len = strlen(passwd);
+
+ if (len > PAM_MAX_RESP_SIZE)
+ len = PAM_MAX_RESP_SIZE;
+ if (write(fds[1], passwd, len) == -1 ||
+ write(fds[1], "", 1) == -1) {
pam_syslog (pamh, LOG_ERR, "Cannot send password to helper: %m");
retval = PAM_AUTH_ERR;
}
Index: pam/modules/pam_unix/pam_unix.8
===================================================================
--- pam.orig/modules/pam_unix/pam_unix.8
+++ pam/modules/pam_unix/pam_unix.8
@@ -56,6 +56,10 @@
\fBnoreap\fR
module argument can be used to suppress this temporary shielding and may be needed for use with certain applications\&.
.PP
+The maximum length of a password supported by the pam_unix module via the helper binary is
+\fIPAM_MAX_RESP_SIZE\fR
+\- currently 512 bytes\&. The rest of the password provided by the conversation function to the module will be ignored\&.
+.PP
The password component of this module performs the task of updating the user\*(Aqs password\&. The default encryption hash is taken from the
\fBENCRYPT_METHOD\fR
variable from
Index: pam/modules/pam_exec/pam_exec.8
===================================================================
--- pam.orig/modules/pam_exec/pam_exec.8
+++ pam/modules/pam_exec/pam_exec.8
@@ -65,7 +65,9 @@
\fBexpose_authtok\fR
.RS 4
During authentication the calling command can read the password from
-\fBstdin\fR(3)\&.
+\fBstdin\fR(3)\&. Only first
+\fIPAM_MAX_RESP_SIZE\fR
+bytes of a password are provided to the command\&.
.RE
.PP
\fBlog=\fR\fB\fIfile\fR\fR
Index: pam/modules/pam_exec/README
===================================================================
--- pam.orig/modules/pam_exec/README
+++ pam/modules/pam_exec/README
@@ -24,7 +24,8 @@
expose_authtok
During authentication the calling command can read the password from stdin
- (3).
+ (3). Only first PAM_MAX_RESP_SIZE bytes of a password are provided to the
+ command.
log=file
Index: pam/modules/pam_unix/README
===================================================================
--- pam.orig/modules/pam_unix/README
+++ pam/modules/pam_unix/README
@@ -34,6 +34,10 @@
suppress this temporary shielding and may be needed for use with certain
applications.
+The maximum length of a password supported by the pam_unix module via the
+helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes. The rest of the
+password provided by the conversation function to the module will be ignored.
+
The password component of this module performs the task of updating the user's
password. The default encryption hash is taken from the ENCRYPT_METHOD variable
from /etc/login.defs
|
