Bug 436893 - pam segfaults on bad input in config file
pam segfaults on bad input in config file
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: pam (Show other bugs)
All Linux
low Severity low
: rc
: ---
Assigned To: Tomas Mraz
Depends On:
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Reported: 2008-03-10 19:04 EDT by David Tonhofer
Modified: 2008-03-27 09:01 EDT (History)
1 user (show)

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Fixed In Version:
Doc Type: Bug Fix
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Last Closed: 2008-03-27 09:01:27 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description David Tonhofer 2008-03-10 19:04:03 EDT
Description of problem:

pam segfaults on bad input 

We have a typo in "/etc/pam.d/su", an 'i' has been left at line 6:

auth       sufficient   /lib/security/$ISA/pam_rootok.so
# Uncomment the following line to implicitly trust users in the "wheel" group.
auth       sufficient   /lib/security/$ISA/pam_wheel.so debug trust use_uid
# Uncomment the following line to require a user to be in the "wheel" group.
i# auth       required     /lib/security/$ISA/pam_wheel.so debug use_uid
auth       required     /lib/security/$ISA/pam_stack.so service=system-auth
account    sufficient   /lib/security/$ISA/pam_succeed_if.so uid=0 use_uid quiet
account    required     /lib/security/$ISA/pam_stack.so service=system-auth
password   required     /lib/security/$ISA/pam_stack.so service=system-auth
# pam_selinux.so close must be first session rule
session    required     /lib/security/$ISA/pam_selinux.so close
session    required     /lib/security/$ISA/pam_stack.so service=system-auth
# pam_selinux.so open and pam_xauth must be last two session rules
session    required     /lib/security/$ISA/pam_selinux.so open
session    optional     /lib/security/$ISA/pam_xauth.so

Executing 'su' then results in a segmentation fault. strace says:

munmap(0xb7d23000, 4096)                = 0
stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=1098, ...}) = 0
stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=1098, ...}) = 0
stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=1098, ...}) = 0
socket(PF_FILE, SOCK_DGRAM, 0)          = 4
fcntl64(4, F_SETFD, FD_CLOEXEC)         = 0
connect(4, {sa_family=AF_FILE, path="/dev/log"}, 16) = 0
send(4, "<11>Mar 11 00:01:41 su: PAM (su)"..., 55, MSG_NOSIGNAL) = 55
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++

A problem with instruction lines should be handled differently than with
SIGSEGV. If the typo is removed, things are well.

Version-Release number of selected component (if applicable):


How reproducible:


See also bug #211756
Comment 1 Ondrej Vasik 2008-03-27 08:34:48 EDT
Thanks for report... similar situation as in #211756.
su is not seg faulting, libpam is ...

gdb reports:
Program received signal SIGSEGV, Segmentation fault.
0x006ec2cd in _pam_strCMP () from /lib/libpam.so.0

Same (or very similar) debian bug report seems to be in

Can't reproduce on my Fedora and RHEL-4 coreutils, so the problem is most
probably not in su. Redirecting component to pam (libpam) as almost certain
cause of crash.
Comment 2 Tomas Mraz 2008-03-27 09:01:27 EDT
This is fixed in later Linux PAM releases (as of RHEL-5 and newer) by changes to
the pam config file parser. The crash is not a security issue because it is only
a NULL pointer dereference. It is also not a DoS because the error in config
file  would cause the authentication fail anyway (in the newer releases).

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