diff mbox

getmntent: fix memory corruption w/blank lines [BZ #18887]

Message ID 1440796961-1773-1-git-send-email-vapier@gentoo.org
State Committed
Delegated to: Mike Frysinger
Headers show

Commit Message

Mike Frysinger Aug. 28, 2015, 9:22 p.m. UTC
The fix for BZ #17273 added 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 does
not really make sense as it's unrelated, and leads to confusing behavior:
it implicitly relies on the new entry being written to the start of the
file being longer than the previous entry since there is no truncation.
Instead split it out into its own dedicated testcase.

2015-08-28  Mike Frysinger  <vapier@gentoo.org>

	[BZ #18887]
	* misc/Makefile (tests): Add tst-mntent-blank-corrupt and
	tst-mntent-blank-passno.
	* misc/mntent_r.c (__getmntent_r): Do not read past buffer[0].
	* misc/tst-mntent-blank-corrupt.c: New test.
	* misc/tst-mntent-blank-passno.c: New test ripped from ...
	* misc/tst-mntent.c (do_test): ... here.
---
 misc/Makefile                   |  3 ++-
 misc/mntent_r.c                 |  4 +++-
 misc/tst-mntent-blank-corrupt.c | 45 ++++++++++++++++++++++++++++++++++
 misc/tst-mntent-blank-passno.c  | 53 +++++++++++++++++++++++++++++++++++++++++
 misc/tst-mntent.c               | 20 ----------------
 5 files changed, 103 insertions(+), 22 deletions(-)
 create mode 100644 misc/tst-mntent-blank-corrupt.c
 create mode 100644 misc/tst-mntent-blank-passno.c

Comments

Ondrej Bilka Aug. 29, 2015, 5:50 a.m. UTC | #1
On Fri, Aug 28, 2015 at 05:22:41PM -0400, Mike Frysinger wrote:
> The fix for BZ #17273 added 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 does
> not really make sense as it's unrelated, and leads to confusing behavior:
> it implicitly relies on the new entry being written to the start of the
> file being longer than the previous entry since there is no truncation.
> Instead split it out into its own dedicated testcase.
>
looks ok.
Mike Frysinger Aug. 29, 2015, 10:19 p.m. UTC | #2
pushed to master & 2.21 & 2.22 since it's a regression from 2.20
-mike
diff mbox

Patch

diff --git a/misc/Makefile b/misc/Makefile
index aecb0da..2f5edf6 100644
--- a/misc/Makefile
+++ b/misc/Makefile
@@ -76,7 +76,8 @@  install-lib := libg.a
 gpl2lgpl := error.c error.h
 
 tests := tst-dirname tst-tsearch tst-fdset tst-efgcvt tst-mntent tst-hsearch \
-	 tst-error1 tst-pselect tst-insremque tst-mntent2 bug-hsearch1
+	 tst-error1 tst-pselect tst-insremque tst-mntent2 bug-hsearch1 \
+	 tst-mntent-blank-corrupt tst-mntent-blank-passno
 ifeq ($(run-built-tests),yes)
 tests-special += $(objpfx)tst-error1-mem.out
 endif
diff --git a/misc/mntent_r.c b/misc/mntent_r.c
index 6159873..4f26998 100644
--- a/misc/mntent_r.c
+++ b/misc/mntent_r.c
@@ -136,7 +136,9 @@  __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')
+	  /* Do not walk past the start of buffer if it's all whitespace.  */
+	  while (end_ptr != buffer
+		 && (end_ptr[-1] == ' ' || end_ptr[-1] == '\t'))
             end_ptr--;
 	  *end_ptr = '\0';
 	}
diff --git a/misc/tst-mntent-blank-corrupt.c b/misc/tst-mntent-blank-corrupt.c
new file mode 100644
index 0000000..92266a3
--- /dev/null
+++ b/misc/tst-mntent-blank-corrupt.c
@@ -0,0 +1,45 @@ 
+/* Make sure blank lines does not cause memory corruption BZ #18887.
+
+   Copyright (C) 2009-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <mntent.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Make sure blank lines don't trigger memory corruption.  This doesn't happen
+   for all targets though, so it's a best effort test BZ #18887.  */
+static int
+do_test (void)
+{
+  FILE *fp;
+
+  fp = tmpfile ();
+  fputs ("\n \n/foo\\040dir /bar\\040dir auto bind \t \n", fp);
+  rewind (fp);
+
+  /* The corruption happens here ...  */
+  getmntent (fp);
+  /* ... but trigers here.  */
+  endmntent (fp);
+
+  /* If the test failed, we would crash, and not hit this point.  */
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/misc/tst-mntent-blank-passno.c b/misc/tst-mntent-blank-passno.c
new file mode 100644
index 0000000..fc04291
--- /dev/null
+++ b/misc/tst-mntent-blank-passno.c
@@ -0,0 +1,53 @@ 
+/* Make sure trailing whitespace is handled properly BZ #17273.
+
+   Copyright (C) 2009-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <mntent.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Check entries to make sure trailing whitespace is ignored and we return the
+   correct passno value BZ #17273.  */
+static int
+do_test (void)
+{
+  int result = 0;
+  FILE *fp;
+  struct mntent *mnt;
+
+  fp = tmpfile ();
+  fputs ("/foo\\040dir /bar\\040dir auto bind \t \n", fp);
+  rewind (fp);
+
+  mnt = getmntent (fp);
+  if (strcmp (mnt->mnt_fsname, "/foo dir") != 0
+      || strcmp (mnt->mnt_dir, "/bar dir") != 0
+      || strcmp (mnt->mnt_type, "auto") != 0
+      || strcmp (mnt->mnt_opts, "bind") != 0
+      || mnt->mnt_freq != 0
+      || mnt->mnt_passno != 0)
+    {
+      puts ("Error while reading entry with trailing whitespaces");
+      result = 1;
+    }
+
+  return result;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/misc/tst-mntent.c b/misc/tst-mntent.c
index 932fd3f..b6ad8af 100644
--- a/misc/tst-mntent.c
+++ b/misc/tst-mntent.c
@@ -73,26 +73,6 @@  do_test (void)
 	  puts ("Error while reading written entry back in");
 	  result = 1;
 	}
-
-      /* Part III: Entry with whitespaces at the end of a line. */
-      rewind (fp);
-
-      fputs ("/foo\\040dir /bar\\040dir auto bind \t \n", fp);
-
-      rewind (fp);
-
-      mnt = getmntent (fp);
-
-      if (strcmp (mnt->mnt_fsname, "/foo dir") != 0
-	  || strcmp (mnt->mnt_dir, "/bar dir") != 0
-	  || strcmp (mnt->mnt_type, "auto") != 0
-	  || strcmp (mnt->mnt_opts, "bind") != 0
-	  || mnt->mnt_freq != 0
-	  || mnt->mnt_passno != 0)
-	{
-	  puts ("Error while reading entry with trailing whitespaces");
-	  result = 1;
-	}
    }
 
   return result;