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From: "kris dot van dot hees at oracle dot com" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sources.redhat.com Subject: [Bug libc/3355] New: strnlen() accesses memory locations beyond (s + maxlen) Date: Thu, 12 Oct 2006 14:50:00 -0000 [thread overview] Message-ID: <20061012145036.3355.kris.van.hees@oracle.com> (raw) Our testing has shown that glibc (all versions since 2.3.2 incl. CVS HEAD as of Oct 12th, 2006 at 10:28 - have not tested earlier versions) implements strnlen() in a way where memory locations (bytes) may be accessed beyond maxlen bytes from the starting pointer. Two problems exist (s is the starting pointer, maxlen is the byte count: 1) The first loop looking at bytes up to the first long-aligned boundary will access bytes up to that boundary, even if (s + maxlen) refers to a memory location between s and the first long-alignment boundary. 2) The second loop (running through the string 4 or 8 bytes at a time) can access memory locations beyond (s + maxlen) if (s + maxlen) does not end at the last byte in a long. In that case, the remaining bytes are still accessed, even though they occur beyond (s + maxlen). The following code fragment shows this problem: ------------------------------------------------------------------------- #include <stdio.h> #include <string.h> #include <stdlib.h> int main() { char *s = (char *)malloc(3); char *t = (char *)malloc(8); s[1] = 'a'; s[2] = 'b'; t[0] = 'a'; t[1] = 'b'; t[2] = 'c'; t[3] = 'd'; t[4] = 'e'; t[5] = '\0'; printf("\t%p -> %ld\n", s + 1, my_strnlen(s + 1, 1)); free(s); printf("\t%p -> %ld\n", t, my_strnlen(t, 0)); printf("\t%p -> %ld\n", t, my_strnlen(t, 1)); printf("\t%p -> %ld\n", t, my_strnlen(t, 2)); printf("\t%p -> %ld\n", t, my_strnlen(t, 3)); printf("\t%p -> %ld\n", t, my_strnlen(t, 4)); printf("\t%p -> %ld\n", t, my_strnlen(t, 5)); free(t); exit(0); } ------------------------------------------------------------------------- The problem is clearly visible when executing this using valgrind *provided* you copy the strnlen() implementation from the glibc sources and renamr the function to be my_strnlen(). Reason for this is that valgrind() otherwise will use its own implementation of strnlen() which is slower but safe. The attached patch file (against CVS) solves the problem with (as far as I can determine) minimal performance impact. -- Summary: strnlen() accesses memory locations beyond (s + maxlen) Product: glibc Version: unspecified Status: NEW Severity: normal Priority: P2 Component: libc AssignedTo: drepper at redhat dot com ReportedBy: kris dot van dot hees at oracle dot com CC: glibc-bugs at sources dot redhat dot com GCC build triplet: i686-pc-linux-gnu GCC host triplet: i686-pc-linux-gnu GCC target triplet: i686-pc-linux-gnu http://sourceware.org/bugzilla/show_bug.cgi?id=3355 ------- You are receiving this mail because: ------- You are on the CC list for the bug, or are watching someone who is.
next reply other threads:[~2006-10-12 14:50 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2006-10-12 14:50 kris dot van dot hees at oracle dot com [this message] 2006-10-12 14:52 ` [Bug libc/3355] " kris dot van dot hees at oracle dot com 2006-10-12 20:48 ` drepper at redhat dot com 2006-10-12 23:48 ` kris dot van dot hees at oracle dot com 2006-10-13 4:31 ` drepper at redhat dot com
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