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7aa867dd89
Daniel Micay reports that attempting to use MAP_FIXED_NOREPLACE in an
application causes that application to randomly crash. The existing check
for handling MAP_FIXED_NOREPLACE looks up the first VMA that either
overlaps or follows the requested region, and then bails out if that VMA
overlaps *the start* of the requested region. It does not bail out if the
VMA only overlaps another part of the requested region.
Fix it by checking that the found VMA only starts at or after the end of
the requested region, in which case there is no overlap.
Test case:
user@debian:~$ cat mmap_fixed_simple.c
#include <sys/mman.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#ifndef MAP_FIXED_NOREPLACE
#define MAP_FIXED_NOREPLACE 0x100000
#endif
int main(void) {
char *p;
errno = 0;
p = mmap((void*)0x10001000, 0x4000, PROT_NONE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED_NOREPLACE, -1, 0);
printf("p1=%p err=%m\n", p);
errno = 0;
p = mmap((void*)0x10000000, 0x2000, PROT_READ,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED_NOREPLACE, -1, 0);
printf("p2=%p err=%m\n", p);
char cmd[100];
sprintf(cmd, "cat /proc/%d/maps", getpid());
system(cmd);
return 0;
}
user@debian:~$ gcc -o mmap_fixed_simple mmap_fixed_simple.c
user@debian:~$ ./mmap_fixed_simple
p1=0x10001000 err=Success
p2=0x10000000 err=Success
10000000-10002000 r--p 00000000 00:00 0
10002000-10005000 ---p 00000000 00:00 0
564a9a06f000-564a9a070000 r-xp 00000000 fe:01 264004
/home/user/mmap_fixed_simple
564a9a26f000-564a9a270000 r--p 00000000 fe:01 264004
/home/user/mmap_fixed_simple
564a9a270000-564a9a271000 rw-p 00001000 fe:01 264004
/home/user/mmap_fixed_simple
564a9a54a000-564a9a56b000 rw-p 00000000 00:00 0 [heap]
7f8eba447000-7f8eba5dc000 r-xp 00000000 fe:01 405885
/lib/x86_64-linux-gnu/libc-2.24.so
7f8eba5dc000-7f8eba7dc000 ---p 00195000 fe:01 405885
/lib/x86_64-linux-gnu/libc-2.24.so
7f8eba7dc000-7f8eba7e0000 r--p 00195000 fe:01 405885
/lib/x86_64-linux-gnu/libc-2.24.so
7f8eba7e0000-7f8eba7e2000 rw-p 00199000 fe:01 405885
/lib/x86_64-linux-gnu/libc-2.24.so
7f8eba7e2000-7f8eba7e6000 rw-p 00000000 00:00 0
7f8eba7e6000-7f8eba809000 r-xp 00000000 fe:01 405876
/lib/x86_64-linux-gnu/ld-2.24.so
7f8eba9e9000-7f8eba9eb000 rw-p 00000000 00:00 0
7f8ebaa06000-7f8ebaa09000 rw-p 00000000 00:00 0
7f8ebaa09000-7f8ebaa0a000 r--p 00023000 fe:01 405876
/lib/x86_64-linux-gnu/ld-2.24.so
7f8ebaa0a000-7f8ebaa0b000 rw-p 00024000 fe:01 405876
/lib/x86_64-linux-gnu/ld-2.24.so
7f8ebaa0b000-7f8ebaa0c000 rw-p 00000000 00:00 0
7ffcc99fa000-7ffcc9a1b000 rw-p 00000000 00:00 0 [stack]
7ffcc9b44000-7ffcc9b47000 r--p 00000000 00:00 0 [vvar]
7ffcc9b47000-7ffcc9b49000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0
[vsyscall]
user@debian:~$ uname -a
Linux debian 4.19.0-rc6+ #181 SMP Wed Oct 3 23:43:42 CEST 2018 x86_64 GNU/Linux
user@debian:~$
As you can see, the first page of the mapping at 0x10001000 was clobbered.
Link: http://lkml.kernel.org/r/20181010152736.99475-1-jannh@google.com
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.