lib/gshadow.c: Don't exit(3) on error in library code

We recently replaced bogus REALLOC() calls that didn't correctly handle
errors.  We replaced them by XREALLOC(), which at least would exit and
avoid triggering undefined or unexpected behavior.

Now that we've made the function way simpler, we can handle these errors
by returning NULL, and handling the NULL in the caller.

Fixes: 4eed3e8 ("lib/gshadow.c: Use XREALLOC() instead of silently continuing on ENOMEM")
Cc: Serge Hallyn <[email protected]>
Signed-off-by: Alejandro Colomar <[email protected]>

lib/gshadow.c

@@ -20,7 +20,6 @@
 
 #include "alloc/malloc.h"
 #include "alloc/realloc.h"
-#include "alloc/x/xmalloc.h"
 #include "defines.h"
 #include "prototypes.h"
 #include "string/strchr/strchrcnt.h"
@@ -39,7 +38,9 @@ build_list(char *s)
 	char    **l;
 	size_t  i;
 
-	l = XMALLOC(strchrcnt(s, ',') + 2, char *);
+	l = MALLOC(strchrcnt(s, ',') + 2, char *);
+	if (l == NULL)
+		return NULL;
 
 	for (i = 0; s != NULL && *s != '\0'; i++)
 		l[i] = strsep(&s, ",");
@@ -110,10 +111,14 @@ sgetsgent(const char *string)
 	sgroup.sg_passwd = fields[1];
 
 	free(sgroup.sg_adm);
-	free(sgroup.sg_mem);
-
 	sgroup.sg_adm = build_list(fields[2]);
+	if (sgroup.sg_adm == NULL)
+		return NULL;
+
+	free(sgroup.sg_mem);
 	sgroup.sg_mem = build_list(fields[3]);
+	if (sgroup.sg_mem == NULL)
+		return NULL;
 
 	return &sgroup;
 }