From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753042AbXCWCuh (ORCPT ); Thu, 22 Mar 2007 22:50:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753061AbXCWCuh (ORCPT ); Thu, 22 Mar 2007 22:50:37 -0400 Received: from nlpi025.sbcis.sbc.com ([207.115.36.54]:56540 "EHLO nlpi025.sbcis.sbc.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753042AbXCWCug (ORCPT ); Thu, 22 Mar 2007 22:50:36 -0400 Message-ID: <4603406E.7030105@gmail.com> Date: Thu, 22 Mar 2007 21:50:22 -0500 From: Bruce Dubbs User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.2pre) Gecko/20070119 SeaMonkey/1.1 MIME-Version: 1.0 To: Nick Piggin CC: linux-kernel@vger.kernel.org Subject: Re: Possible Bug in mincore or mmap References: <4602D6FD.6030505@gmail.com> <460324DF.6040109@yahoo.com.au> In-Reply-To: <460324DF.6040109@yahoo.com.au> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > Bruce Dubbs wrote: >> When testing an installation with tests from the Linux Test Project, my >> kernels fail one instance of the mincore01 tests: >> >> mincoremincore01 1 PASS : expected failure: errno = 22 (Invalid >> argument) >> mincore01 2 PASS : expected failure: errno = 14 (Bad address) >> mincore01 3 FAIL : call succeeded unexpectedly >> mincore01 4 PASS : expected failure: errno = 12 (Cannot allocate >> memory)01 1 PASS : expected failure: errno = 22 (Invalid argument) >> mincore01 2 PASS : expected failure: errno = 14 (Bad address) >> mincore01 3 FAIL : call succeeded unexpectedly >> mincore01 4 PASS : expected failure: errno = 12 (Cannot allocate >> memory) >> >> I pared down the test to the attached program. The result is supposed >> to fail as it is asking for memory information 5 times what should be >> allocated. >> >> Upon experimenting, I found the test works properly if a printf is >> executed before the mmap call. I have tested on locally built, but >> unmodified, 2.4.25, 2.6.12.5, and a 2.6.20.3 kernels and get the same >> behavior. The tests fail on IA32 architecture, but not 64-bit kernels. >> The test always works properly on FC6 and RHEL3. >> >> I've checked the archives for this issue and could not find anything >> appropriate. >> >> Could this be a potential security issue as memory that is not supposed >> to be accessible seems to be available to the user? Is it expected >> behavior? > > It shouldn't be a security problem if mincore doesn't actually > return the data. Thanks for the response. It may be interesting to note that adding: buf = (char*)global_pointer + 2 * global_len; i = *buf; after the mincore call does not fail. Changing the 2nd line above to *buf = 1; gives a segmentation fault as you would expect. As a minimum, it appears the mmap function is allowing read access beyond its allocated address space in some circumstances. Upon thinking about it, it may be that the test is invalid. I don't believe there is anything tying the mincore query to the memory region allocated by mmap. If memory mapping occurs beyond the mmap requested memory size to anticipate another memory request, mincore wouldn't fail. Does this make any sense? >> ------------------------------------------------------------------------ >> >> #include >> #include >> #include >> #include >> >> static int PAGESIZE; >> static char file_name[] = "fooXXXXXX"; >> static void* global_pointer = NULL; >> static int global_len = 0; >> static int file_desc = 0; >> >> int main(int argc, char **argv) >> { >> int i; >> int result; >> char* buf; >> unsigned char vect[20] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}; >> >> PAGESIZE = getpagesize(); >> /* global_pointer will point to a mmapped area of global_len >> bytes */ >> global_len = PAGESIZE*2; >> buf = (char*)malloc(global_len); >> memset(buf, 42, global_len); // Asterisks /* create a >> temporary file */ >> file_desc = mkstemp(file_name); >> /* fill the temporary file with two pages of data */ >> write(file_desc, buf, global_len); >> free(buf); >> // Will work properly as long as print is before mmap function. >> if ( argc > 1 ) printf("argc=%d\n", argc); >> >> /* map the file in memory */ >> global_pointer = mmap( NULL, global_len, >> PROT_READ|PROT_WRITE|PROT_EXEC, MAP_SHARED, file_desc, 0); >> >> // Result should be -1 as the request is 5 times actual mapping >> result = mincore(global_pointer, (size_t)(global_len*5), vect); >> >> // Print some data >> printf("PAGESIZE=%d\n", PAGESIZE); >> printf("global_len=%d\n", global_len); >> printf("global_pointer=0x%x\n", (unsigned int)global_pointer); >> printf("alloc=%d\n", (global_len+PAGESIZE-1) / PAGESIZE ); >> printf("Result=%d\n", result); >> printf("vect: "); >> >> for ( i=0; i<20; i++) printf("%02x ", vect[i]); >> printf("\n"); >> // Clean up >> munmap(global_pointer, (size_t)global_len); >> close(file_desc); >> unlink(file_name); >> } > >