svn commit: r256537 - head/lib/libc/gen

[Gleb Smirnoff]

Author: glebius
Date: Tue Oct 15 13:32:01 2013
New Revision: 256537
URL: http://svnweb.freebsd.org/changeset/base/256537

Log:
    Make getutxent(3) more robust against bad utx.log files. Whenever we read
  zeroes, don't stop processing the file, but read until its end or valid
  data.
  
  In collaboration with:	ed

Modified:
  head/lib/libc/gen/getutxent.c

Modified: head/lib/libc/gen/getutxent.c
==============================================================================
--- head/lib/libc/gen/getutxent.c	Tue Oct 15 13:24:10 2013	(r256536)
+++ head/lib/libc/gen/getutxent.c	Tue Oct 15 13:32:01 2013	(r256537)
@@ -122,9 +122,20 @@ getfutxent(struct futx *fu)
 	if (udb == UTXDB_LOG) {
 		uint16_t len;
 
+retry:
 		if (fread(&len, sizeof(len), 1, uf) != 1)
 			return (-1);
 		len = be16toh(len);
+		if (len == 0) {
+			/*
+			 * XXX: Though zero-size records are valid in theory,
+			 * they can never occur in practice. Zero-size records
+			 * indicate file corruption. Seek one byte forward, to
+			 * see if we can find a record there.
+			 */
+			ungetc('\0', uf);
+			goto retry;
+		}
 		if (len > sizeof *fu) {
 			/* Forward compatibility. */
 			if (fread(fu, sizeof(*fu), 1, uf) != 1)