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Re: [PATCH] Check for overflow in __alloc_dir
On 10/12/2012 07:57 PM, Roland McGrath wrote:
On 10/12/2012 04:54 PM, Roland McGrath wrote:
Use a macro for the constant and give it a comment about the choice of value.
Don't ignore a large st_blksize, just use MAX (st_blksize, MAX_ALLOCATION).
Sorry, I don't understand. Do you mean MIN (st_blksize, MAX_ALLOCATION)?
Yes, sorry.
Is this what you had in mind?
I no longer use MIN/MAX for clamping because it's so counter-intuitive.
As far as I can tell, this doesn't cause any regressions on
x86_64-redhat-linux-gnu.
--
Florian Weimer / Red Hat Product Security Team
2012-10-15 Florian Weimer <fweimer@redhat.com>
[BZ #14700]
* sysdeps/posix/opendir.c (MAX_DIR_BUFFER_SIZE): New constant.
(__alloc_dir): Limit buffer to MAX_DIR_BUFFER_SIZE.
diff --git a/sysdeps/posix/opendir.c b/sysdeps/posix/opendir.c
index e093142..f1cc1ae 100644
--- a/sysdeps/posix/opendir.c
+++ b/sysdeps/posix/opendir.c
@@ -1,5 +1,4 @@
-/* Copyright (C) 1991-1996,98,2000-2003,2005,2007,2009,2011
- Free Software Foundation, Inc.
+/* Copyright (C) 1991-2012 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
@@ -33,6 +32,11 @@
#include <not-cancel.h>
#include <kernel-features.h>
+/* The st_blksize value of the directory is used as a hint for the
+ size of the buffer which receives struct dirent values from the
+ kernel. st_blksize is limited to MAX_DIR_BUFFER_SIZE, in case the
+ file system provides a bogus value. */
+#define MAX_DIR_BUFFER_SIZE 1048576U
/* opendir() must not accidentally open something other than a directory.
Some OS's have kernel support for that, some don't. In the worst
@@ -192,8 +196,11 @@ __alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
? sizeof (struct dirent64) : BUFSIZ);
size_t allocation = default_allocation;
#ifdef _STATBUF_ST_BLKSIZE
- if (statp != NULL && default_allocation < statp->st_blksize)
- allocation = statp->st_blksize;
+ /* Increase allocation if requested, but not if the value appears to
+ be bogus. */
+ if (statp != NULL)
+ allocation = MIN (MAX ((size_t) statp->st_blksize, default_allocation),
+ MAX_DIR_BUFFER_SIZE);
#endif
DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);