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Re: Ad PR libc/1730: glibc bug in memmem()
- To: Greg Hudson <ghudson at mit dot edu>
- Subject: Re: Ad PR libc/1730: glibc bug in memmem()
- From: Andreas Jaeger <aj at suse dot de>
- Date: 17 May 2000 18:05:36 +0200
- Cc: libc-alpha Mailinglist <libc-alpha at sourceware dot cygnus dot com>
- References: <200005171406.KAA28210@small-gods.mit.edu>
>>>>> Greg Hudson writes:
Greg> The code part of the patch looks fine. (I would probably avoid even
Greg> computing the invalid pointer value in the haystack_len < needle_len,
Greg> but I hardly think that's important.)
>> * sysdeps/generic/memmem.c (memmem): Check for invalid parameter.
Greg> I don't think having haystack_len < needle_len constitutes an invalid
Greg> parameter.
>> + /* Sanity check, otherwise the loop will search through the whole
>> + memory. */
Greg> This comment might be confusing to some readers. On most C
Greg> implementations, most of the time, the loop will not search through
Greg> the whole memory. The particular case that bit me was that haystack
Greg> was NULL (the result of malloc(0)), so the invalid computed pointer
Greg> wrapped around to a very high value.
Greg> Replacing "will" with "might" would probably fix the situation.
Greg> Sorry to nitpick so much. Thanks for your time.
I agree with Mark here ;-). You're welcome.
Any problems with the appended patch? I've optimized even a little
bit.
Andreas
* sysdeps/generic/memmem.c (memmem): Check arguments to avoid
possibly searching through the whole memory.
Closes PR libc/1730, reported by Greg Hudson <ghudson@mit.edu>.
============================================================
Index: sysdeps/generic/memmem.c
--- sysdeps/generic/memmem.c 1998/01/30 13:39:22 1.10
+++ sysdeps/generic/memmem.c 2000/05/17 16:05:25
@@ -1,4 +1,4 @@
-/* Copyright (C) 1991, 92, 93, 94, 96, 97, 98 Free Software Foundation, Inc.
+/* Copyright (C) 1991,92,93,94,96,97,98,2000 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
@@ -37,6 +37,11 @@
/* The first occurrence of the empty string is deemed to occur at
the beginning of the string. */
return (void *) haystack;
+
+ /* Sanity check, otherwise the loop might search through the whole
+ memory. */
+ if (__builtin_expect (haystack_len < needle_len, 0))
+ return NULL;
for (begin = (const char *) haystack; begin <= last_possible; ++begin)
if (begin[0] == ((const char *) needle)[0] &&
--
Andreas Jaeger
SuSE Labs aj@suse.de
private aj@arthur.inka.de