From b0e805fa0d6fea33745952df7b7f5442ca4c374f Mon Sep 17 00:00:00 2001
From: Mike Frysinger <vapier@gentoo.org>
Date: Fri, 28 Aug 2015 17:08:49 -0400
Subject: [PATCH] getmntent: fix memory corruption w/blank lines [BZ #18887]

The fix for BZ #17273 introduced a single byte of memory corruption when
the line is entirely blank.  It would walk back past the start of the
buffer if the heap happened to be 0x20 or 0x09 and then write a NUL byte.
       buffer = '\n';
       end_ptr = buffer;
       while (end_ptr[-1] == ' ' || end_ptr[-1] == '\t')
       	     end_ptr--;
	     *end_ptr = '\0';

Fix that and rework the tests.  Adding the testcase for BZ #17273 to the
existing \040 parser does not really make sense as it's unrelated, and
leads to confusing behavior: it implicitly relies on the new entry being
longer than the previous entry (since it just rewinds the FILE*).  Split
it out into its own dedicated testcase instead.

The original patch is at link https://sourceware.org/git/gitweb.cgi?p=glibc.git;a=patch;h=b0e805fa0d6fea33745952df7b7f5442ca4c374f.
Only code to mntent_r.c is kept in this patch, Change log, NEWS, Makefile, and test cases are excluded.

Upstream-Status: Backport (upstreamed to 2.23)
Signed-off-by: Baoshan Pang <baoshan.pang@windriver.com>

diff --git a/misc/mntent_r.c b/misc/mntent_r.c
index 6159873..19af8a8 100644
--- a/misc/mntent_r.c
+++ b/misc/mntent_r.c
@@ -136,7 +136,8 @@ __getmntent_r (FILE *stream, struct mntent *mp, char *buffer, int bufsiz)
       end_ptr = strchr (buffer, '\n');
       if (end_ptr != NULL)	/* chop newline */
 	{
-	  while (end_ptr[-1] == ' ' || end_ptr[-1] == '\t')
+	  while (end_ptr != buffer
+		 && (end_ptr[-1] == ' ' || end_ptr[-1] == '\t'))
             end_ptr--;
 	  *end_ptr = '\0';
 	}