Package: libpam-mount
Version: 0.44-1+lenny3
Severity: important
Tags: patch
Per cron bug 484122 some (all?) users who are mounting their encrypted home
directory with libpam-mount have been seeing a constant stream of segfaults
in cron. Cron has been rendered useless in this environment.
strace and ltrace did not yield any interesting results so I have used gdb
to localize the problem and propose a solution.
This patch seems to fix the problem for me:
----------------
diff --git a/src/pam_mount.c b/src/pam_mount.c
index 211a996..b86cd05 100644
--- a/src/pam_mount.c
+++ b/src/pam_mount.c
@@ -156,7 +156,7 @@ static int converse(pam_handle_t *pamh, int nargs,
retval = pam_get_item(pamh, PAM_CONV, static_cast(const void **,
static_cast(void *, &conv)));
- if (retval == PAM_SUCCESS) {
+ if (retval == PAM_SUCCESS && *resp != NULL) {
retval = conv->conv(nargs, message, resp,
conv->appdata_ptr);
if (retval != PAM_SUCCESS)
l0g("conv->conv(...): %s\n", pam_strerror(pamh,
retval));
----------------
There is another call to pam_get_item on line 270 of the same file which was
suggestive of the necessary fix. Not understanding the software fully, I
made the above minimal change, and it seems to be sufficient, though I
continue to run with it and test.
This is my first patch submission to Debian, and I am treading in software
that I do not really understand, so following is a verbose transcript of my
gdb session:
(gdb) attach 3489
Attaching to process 3489
Reading symbols from /usr/sbin/cron...done.
Reading symbols from /lib/libpam.so.0...done.
Loaded symbols for /lib/libpam.so.0
Reading symbols from /lib/libselinux.so.1...done.
Loaded symbols for /lib/libselinux.so.1
Reading symbols from /lib/i686/cmov/libc.so.6...done.
Loaded symbols for /lib/i686/cmov/libc.so.6
Reading symbols from /lib/i686/cmov/libdl.so.2...done.
Loaded symbols for /lib/i686/cmov/libdl.so.2
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
Reading symbols from /lib/i686/cmov/libnss_compat.so.2...done.
Loaded symbols for /lib/i686/cmov/libnss_compat.so.2
Reading symbols from /lib/i686/cmov/libnsl.so.1...done.
Loaded symbols for /lib/i686/cmov/libnsl.so.1
Reading symbols from /lib/i686/cmov/libnss_nis.so.2...done.
Loaded symbols for /lib/i686/cmov/libnss_nis.so.2
Reading symbols from /lib/i686/cmov/libnss_files.so.2...done.
Loaded symbols for /lib/i686/cmov/libnss_files.so.2
0xb7f5e424 in __kernel_vsyscall ()
(gdb) set follow-fork-mode child
(gdb) cont
Continuing.
Program received signal SIGSEGV, Segmentation fault.
[Switching to process 19892]
0x00000000 in ?? ()
(gdb)
(gdb) info frame 0
Stack frame at 0xbfba1aa0:
eip = 0x0; saved eip 0xb7b4cda1
called by frame at 0xbfba1af0
Arglist at 0xbfba1a98, args:
Locals at 0xbfba1a98, Previous frame's sp is 0xbfba1aa0
Saved registers:
eip at 0xbfba1a9c
(gdb) up
#1 0xb7b4cda1 in read_password (pamh=0x8841b00,
prompt=0x8846278 "reenter password for pam_mount:", pass=0xbfba1b38)
at pam_mount.c:160
160 retval = conv->conv(nargs, message, resp,
conv->appdata_ptr);
(gdb) up
#2 0xb7b4ddf3 in pam_sm_open_session (pamh=0x8841b00, flags=32768, argc=1,
argv=0x8843ce0) at pam_mount.c:511
511 ret = read_password(pamh, Config.msg_sessionpw,
&system_authtok);
(gdb) up
#3 0xb7f693c1 in _pam_dispatch (pamh=0x8841b00, flags=32768, choice=4)
at pam_dispatch.c:108
108 retval = h->func(pamh, flags, h->argc, h->argv);
(gdb) up
#4 0xb7f6cfeb in pam_open_session (pamh=0x8841be8, flags=32768)
at pam_session.c:23
23 retval = _pam_dispatch(pamh, flags, PAM_OPEN_SESSION);
(gdb) up
#5 0x0804e848 in child_process (e=0x88418f8, u=0x88418d8) at
.../do_command.c:228
228 retcode = pam_open_session(pamh, PAM_SILENT);
(gdb) up
#6 0x0804e36d in do_command (e=0x88418f8, u=0x88418d8) at
.../do_command.c:102
102 child_process(e, u);
(gdb) up
#7 0x0804e1e3 in job_runqueue () at ../job.c:68
68 do_command(j->e, j->u);
(gdb) up
#8 0x0804a777 in main (argc=142875624, argv=0x0) at ../cron.c:270
270 job_runqueue();
(gdb) up
Initial frame selected; you cannot go up.
(gdb) frame 0
#0 0x00000000 in ?? ()
(gdb) up
#1 0xb7b4cda1 in read_password (pamh=0x8841b00,
prompt=0x8846278 "reenter password for pam_mount:", pass=0xbfba1b38)
at pam_mount.c:160
160 retval = conv->conv(nargs, message, resp,
conv->appdata_ptr);
(gdb) list
155 *resp = NULL;
156 retval = pam_get_item(pamh, PAM_CONV, static_cast(const void
**,
157 static_cast(void *, &conv)));
158
159 if (retval == PAM_SUCCESS) {
160 retval = conv->conv(nargs, message, resp,
conv->appdata_ptr);
161 if (retval != PAM_SUCCESS)
162 l0g("conv->conv(...): %s\n",
pam_strerror(pamh, retval));
163 } else {
164 l0g("pam_get_item: %s\n", pam_strerror(pamh,
retval));
(gdb)
(gdb) print *resp
Cannot access memory at address 0x0
(gdb) print resp
$3 = (struct pam_response *) 0x0
(gdb)
-- System Information:
Debian Release: 5.0
APT prefers testing
APT policy: (500, 'testing')
Architecture: i386 (i686)
Kernel: Linux 2.6.26-1-686 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
Versions of packages libpam-mount depends on:
ii debconf 1.5.24 Debian configuration management sy
ii libc6 2.7-16 GNU C Library: Shared libraries
ii libhx13 1.18-1 A library providing queue, tree, I
ii libpam0g 1.0.1-4 Pluggable Authentication Modules l
ii libssl0.9.8 0.9.8g-14 SSL shared libraries
ii libxml-writer-perl 0.604-1 Perl module for writing XML docume
ii libxml2 2.6.32.dfsg-5 GNOME XML library
ii mount 2.13.1.1-1 Tools for mounting and manipulatin
libpam-mount recommends no packages.
Versions of packages libpam-mount suggests:
ii cryptsetup 2:1.0.6-7 configures encrypted block devices
pn davfs2 <none> (no description available)
ii fuse-utils 2.7.4-1.1 Filesystem in USErspace (utilities
ii lsof 4.78.dfsg.1-4 List open files
pn ncpfs <none> (no description available)
ii openssl 0.9.8g-14 Secure Socket Layer (SSL) binary a
ii psmisc 22.6-1 Utilities that use the proc filesy
pn smbfs <none> (no description available)
pn truecrypt-utils <none> (no description available)
-- debconf information:
* libpam-mount/convert-xml-config: true
diff --git a/src/pam_mount.c b/src/pam_mount.c
index 211a996..b86cd05 100644
--- a/src/pam_mount.c
+++ b/src/pam_mount.c
@@ -156,7 +156,7 @@ static int converse(pam_handle_t *pamh, int nargs,
retval = pam_get_item(pamh, PAM_CONV, static_cast(const void **,
static_cast(void *, &conv)));
- if (retval == PAM_SUCCESS) {
+ if (retval == PAM_SUCCESS && *resp != NULL) {
retval = conv->conv(nargs, message, resp, conv->appdata_ptr);
if (retval != PAM_SUCCESS)
l0g("conv->conv(...): %s\n", pam_strerror(pamh, retval));
