[Bug libc/15560] New: munmap subregion of memory maped by mmap

[Bug libc/15560] New: munmap subregion of memory maped by mmap

[zylcf818 at 163 dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15560

            Bug ID: 15560
           Summary: munmap subregion of memory maped by mmap
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: minor
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: zylcf818 at 163 dot com
                CC: drepper.fsp at gmail dot com

in rhel6.2, I mmap 3 pages, and munmap the middle page, but the behavior of
munmap() seems to be strange, below is code:
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <cstring>

int main(int argc, char *argv[])
{
    char* addr = (char*)mmap(NULL, 4096*3, PROT_READ|PROT_WRITE,
        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); 
    if (addr == MAP_FAILED)
        printf("Failed to mmap\n");

    memcpy(addr, "abc", 3); 
    memcpy(addr+4096, "def", 3); 
    memcpy(addr+8192, "ghi", 3); 

//    printf("%10p\n", addr);
//    printf("%10p\n", addr+4096);
//    printf("%10p\n", addr+8192);

//    printf("%s\n", addr);
//    printf("%s\n", addr+4096);
//    printf("%s\n", addr+8192);

    int rs = munmap(addr+4096, 4096);
    if ( rs != 0 ) 
        printf("failed to munmap\n");

    printf("%s\n", addr);
    printf("%s\n", addr+4096);
    printf("%s\n", addr+8192);

    memcpy(addr, "123", 3); 
    memcpy(addr+4096, "456", 3); 
    memcpy(addr+8192, "789", 3); 

    printf("%s\n", addr);
    printf("%s\n", addr+4096);
    printf("%s\n", addr+8192);

    exit(EXIT_SUCCESS);
} /* main */

>g++ -g -o mmap mmap.cpp
>./mmap
abc
abc

ghi
123
123

789
if I comment off printf... in code, the result is what I expect:
0x7f3c4a274000
0x7f3c4a275000
0x7f3c4a276000
abc
def
ghi
abc
Segmentation fault (core dumped) <---  what I expect

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[Bug libc/15560] munmap subregion of memory maped by mmap

[zylcf818 at 163 dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15560

--- Comment #1 from zhangyue <zylcf818 at 163 dot com> ---
Maybe I report this problem to kernel guys?

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[Bug libc/15560] munmap subregion of memory maped by mmap

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=15560

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
The compiler is optimizing out the memory loads, which is a perfectly valid
transformation in the presense of undefined behaviour.

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[Bug libc/15560] munmap subregion of memory maped by mmap

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15560

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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