Messages in this thread | | | Date | Tue, 23 Mar 2010 11:48:06 +0800 | Subject | Re: [PATCH] Netfilter: Fix integer overflow in net/ipv6/netfilter/ip6_tables.c | From | wzt wzt <> |
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1、 suppose *len = 35, sizeof(struct ipt_get_entries) = 36 2、 set get.size = 0xffffffff from user space 3、 sizeof(struct ipt_get_entries) + get.size = 36 + 0xffffffff = 35; 4、 if (*len != sizeof(struct ipt_get_entries) + get.size) was bypassed.
you can test with c code:
#include <stdio.h>
int main(void) { unsigned int arg = 0xffffffff;
printf("%u\n", arg + 36); if (35 != arg + 36) { printf("not over flow.\n"); return -1; } printf("arg over flow.\n");
return 0; }
On Tue, Mar 23, 2010 at 11:04 AM, Jan Engelhardt <jengelh@medozas.de> wrote: > > On Tuesday 2010-03-23 03:37, wzt wzt wrote: >>> And, for the addition overflow, can it be caught by >>> >>> "if (*len != sizeof(struct ipt_get_entries) + get.size)" ??? >> >>sizeof(struct ipt_get_entries) + get.size can be overflow as *len, >>get.size is control by user space with copy_from_user(). > > The != should catch it. > > For 64-bit environments: > * + invoked with size_t, unsigned int > => right side promoted to size_t, result type is size_t > * != invoked with int and size_t > => left-side promoted to ssize_t (probably; but something as large as size_t) > * get.size is 32-bit bounded, as is *len, > so no overflow to worry about at all unless you make > sizeof(X) hilariously big close to 2^64 which is rather unlikely. > > For 32-bit environments: > * Let *len be a number of choice (e.g. 36) > * Find a sizeof(X)+get.size that equals 36 mod 2^32. > * Since sizeof(X) is const, get.size must be 0 mod 2^32. > * So get.size must be a multiple of 2^32 to fool the system. > * Since get.size itself is only a 32-bit quantity, you cannot > represent any value larger than 4294967295. > > > What Was What Was Wanted. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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