[Bug 513497] [NEW] empty fields in shadow handled wrongly

[James Pharaoh]

Public bug reported:

Binary package hint: libnss-extrausers

When reading shadow, integer fields are read with strtol directly. This
produces 0 for an empty field. However, in many cases a -1 should be
used for an empty field. This is certainly the case for account expiry,
the final field. This can be seen in the code in glibc which loads these
fields:

eglibc-2.10.1/shadow/sgetspent_r.c:

         INT_FIELD_MAYBE_NULL (result->sp_expire, ISCOLON, 0, 10, (long int),
                               (long int) -1);
 
In the definition of INT_FIELD_MAYBE_NULL the last field is called default.

pam_unix is interpreting this 0 value as an account expiring on the 1st
of January 1970 which of course is always in the past and so all
accounts are appearing expired.

Other fields which default to -1 are sp_lstchg, sp_min, sp_max, sp_warn
and sp_inact.

A workaround for this is to set a value in this field.

A fix is the following patch:

diff -U3 -r libnss-extrausers-0.2-orig/shadow.c libnss-extrausers-0.2/shadow.c
--- libnss-extrausers-0.2-orig/shadow.c	2010-01-27 22:07:04.064336148 +0000
+++ libnss-extrausers-0.2/shadow.c	2010-01-27 22:19:38.122475198 +0000
@@ -118,27 +118,33 @@
 		TOCOLON(p,h);
 		/* extract day of last changes */
 		t_lstchg = strtol(p,&h,10);
+		if (p == h) t_lstchg = -1;
 		p=h;
 		CHECKCOLON;
 		p = ++h;
 		/* extract min */
 		t_min = strtol(p,&h,10);
+		if (p == h) t_min = -1;
 		p=h;
 		CHECKCOLON;
 		/* extract max */
 		t_max = strtol(p,&h,10);
+		if (p == h) t_max = -1;
 		p=h;
 		CHECKCOLON;
 		/* extract days of warning */
 		t_warn = strtol(p,&h,10);
+		if (p == h) t_warn = -1;
 		p=h;
 		CHECKCOLON;
 		/* extract days of inactivity */
 		t_inact = strtol(p,&h,10);
+		if (p == h) t_inact = -1;
 		p=h;
 		CHECKCOLON;
 		/* extract day of expire */
 		t_expire = strtol(p,&h,10);
+		if (p == h) t_expire = -1;
 		p=h;
 		CHECKCOLON;
 		/* extract reserved flags */

I wonder if it's actually possible to use the shadow reading code in
glibc instead of doing this separately? I don't have time to look into
that now anyway.

** Affects: libnss-extrausers (Ubuntu)
     Importance: Undecided
         Status: New

-- 
empty fields in shadow handled wrongly
https://bugs.launchpad.net/bugs/513497
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