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From: "shaun.colley at ioactive dot com" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sources.redhat.com Subject: [Bug libc/14552] New: Two security issues in strcoll() function Date: Thu, 06 Sep 2012 16:18:00 -0000 [thread overview] Message-ID: <bug-14552-131@http.sourceware.org/bugzilla/> (raw) http://sourceware.org/bugzilla/show_bug.cgi?id=14552 Bug #: 14552 Summary: Two security issues in strcoll() function Product: glibc Version: 2.17 Status: NEW Severity: normal Priority: P2 Component: libc AssignedTo: unassigned@sourceware.org ReportedBy: shaun.colley@ioactive.com CC: drepper.fsp@gmail.com Classification: Unclassified There are two problems with the strcoll() interface. 1) alloca() stack overflow If the malloc() call fails (i.e. OOM conditions), strcoll() will failsafe back to alloca(), which could result in unbounded alloca() calls and exploitable conditions if the stack pointer is shifted over the guard area and into the heap. See vulnerable code below. if (idx1arr == NULL) // [5] memory allocation failed, use alloca() ... /* No memory. Well, go with the stack then. XXX Once this implementation is stable we will handle this differently. Instead of precomputing the indeces we will do this in time. This means, though, that this happens for every pass again. */ goto try_stack; use_malloc = 1; } else { try_stack: idx1arr = (int32_t *) alloca (s1len * sizeof (int32_t)); // [6] stack pointer shifting idx2arr = (int32_t *) alloca (s2len * sizeof (int32_t)); rule1arr = (unsigned char *) alloca (s1len); rule2arr = (unsigned char *) alloca (s2len); Here's my testcase. #include <stdio.h> #include <stdlib.h> #include <string.h> #include <locale.h> #define LEN 500000 int main() { char *ptr1 = malloc(LEN + 1); char *ptr2 = malloc(LEN + 1); char *wasted = NULL; int i = 0, ret = 0; if(!ptr1 || !ptr2) { printf("memory allocation failed\n"); return -1; } memset(ptr1, 0x61, LEN); memset(ptr2, 0x61, LEN); ptr1[LEN] = 0; ptr2[LEN] = 0; printf("strings allocated\n"); char *ptr = setlocale(LC_ALL, "en_US.UTF-8"); if(!ptr) { printf("error setting locale\n"); return -1; } /* malloc() big chunks until we're out of memory */ do { wasted = malloc(1000000); printf("%p\n", wasted); i++; } while(wasted); ret = strcoll(ptr1, ptr2); if(!ret) { printf("strings were lexicographically identical\n"); } else { printf("strings were different\n"); } return 0; } 2) Integer overflows in the malloc() memory allocation. int STRCOLL (s1, s2, l) const STRING_TYPE *s1; const STRING_TYPE *s2; __locale_t l; { [ … ] /* We need this a few times. */ s1len = STRLEN (s1); s2len = STRLEN (s2); [ … ] Please note that the localedef programs makes sure that `position' is not used at the first level. */ if (! __libc_use_alloca ((s1len + s2len) * (sizeof (int32_t) + 1))) // [1] if arithmetic is greater 65536, use malloc() instead of alloca() { idx1arr = (int32_t *) malloc ((s1len + s2len) * (sizeof (int32_t) + 1)); // [2] attempt to get memory using malloc() If s1 and s2 point to long strongs, the arithmetic in the malloc() argument may give an integer overflow, and result in subsequent heap corruption. Cheers, Shaun -- Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.
next reply other threads:[~2012-09-06 16:18 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-09-06 16:18 shaun.colley at ioactive dot com [this message] 2012-09-06 16:22 ` [Bug libc/14552] " shaun.colley at ioactive dot com 2012-09-06 16:54 ` jsm28 at gcc dot gnu.org 2014-06-17 4:45 ` fweimer at redhat dot com 2015-02-24 11:35 ` fweimer at redhat dot com
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