login: rewrite is_local() to remove limits on line length

Signed-off-by: James Youngman <jay@gnu.org>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 84 insertions, 21 deletions

diff --git a/login-utils/islocal.c b/login-utils/islocal.c
index 297698041..762a4e990 100644
--- a/login-utils/islocal.c
+++ b/login-utils/islocal.c
@@ -12,7 +12,10 @@
 
    1999-02-22 Arkadiusz Mi¶kiewicz <misiek@pld.ORG.PL>
    - added Native Language Support
-     
+
+   2008-04-06 James Youngman, jay@gnu.org
+   - Completely rewritten to remove assumption that /etc/passwd
+     lines are < 1024 characters long.  Also added unit tests.
 
 */
 
@@ -24,29 +27,89 @@
 #include "pathnames.h"
 #include "islocal.h"
 
-#define MAX_LENGTH	1024
-
-int
-is_local(char *user)
+static int
+is_local_in_file(const char *user, const char *filename)
 {
-	FILE *fd;
-	char line[MAX_LENGTH];
 	int local = 0;
-	size_t len;
-
-        if(!(fd = fopen(_PATH_PASSWD, "r"))) {
-                fprintf(stderr,_("Can't read %s, exiting."),_PATH_PASSWD);
-                exit(1);
-        }
-
-	len = strlen(user);
-        while(fgets(line, MAX_LENGTH, fd)) {
-                if(!strncmp(line, user, len) && line[len] == ':') {
-			local = 1;
-			break;
-                }
+	size_t match;
+	int chin, skip;
+	FILE *f;
+
+        if (NULL == (f=fopen(filename, "r")))
+                return -1;
+
+	match = 0u;
+	skip = 0;
+	while ((chin = getc(f)) != EOF) {
+		if (skip) {
+			/* Looking for the start of the next line. */
+			if ('\n' == chin) {
+				/* Start matching username at the next char. */
+				skip = 0;
+				match = 0u;
+			}
+		} else {
+			if (':' == chin) {
+				if (0 == user[match]) {
+					local = 1; /* Success. */
+					/* next line has no test coverage, but it is
+					 * just an optimisation anyway. */
+					break;
+				} else {
+					/* we read a whole username, but it is
+					 * the wrong user.  Skip to the next
+					 * line. */
+					skip = 1;
+				}
+			} else if ('\n' == chin) {
+				/* This line contains no colon; it's malformed.
+				 * No skip since we are already at the start of
+				 * the next line. */
+				match = 0u;
+			} else if (chin != user[match]) {
+				/* username does not match. */
+				skip = 1;
+			} else {
+				++match;
+			}
+		}
 	}
-	fclose(fd);
+	fclose(f);
 	return local;
 }
 
+int
+is_local(const char *user)
+{
+	int rv;
+	if ((rv = is_local_in_file(user, _PATH_PASSWD)) < 0) {
+		perror(_PATH_PASSWD);
+		fprintf(stderr, _("Failed to open %s for reading, exiting."),
+			_PATH_PASSWD);
+		exit(1);
+	} else {
+		return rv;
+	}
+}
+
+#if MAIN_TEST_ISLOCAL
+int
+main (int argc, char *argv[])
+{
+	if (argc < 2) {
+		fprintf(stderr, "No test passwd file was specified.\n");
+		return 1;
+	} else {
+		int i;
+		for (i = 2; i < argc; i++) {
+			const int rv = is_local_in_file(argv[i], argv[1]);
+			if (rv < 0) {
+				perror(argv[1]);
+				return 2;
+			}
+			printf("%d:%s\n", rv, argv[i]);
+		}
+		return 0;
+	}
+}
+#endif