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brk: fix min_brk lower bound computation for COMPAT_BRK 

Even if CONFIG_COMPAT_BRK is set in the kernel configuration, it can still
be overriden by randomize_va_space sysctl.

If this is the case, the min_brk computation in sys_brk() implementation
is wrong, as it solely takes into account COMPAT_BRK setting, assuming
that brk start is not randomized.  But that might not be the case if
randomize_va_space sysctl has been set to '2' at the time the binary has
been loaded from disk.

In such case, the check has to be done in a same way as in
!CONFIG_COMPAT_BRK case.

In addition to that, the check for the COMPAT_BRK case introduced back in
a5b4592c ("brk: make sys_brk() honor COMPAT_BRK when computing lower
bound") is slightly wrong -- the lower bound shouldn't be mm->end_code,
but mm->end_data instead, as that's where the legacy applications expect
brk section to start (i.e.  immediately after last global variable).

[akpm@linux-foundation.org: fix comment]
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jiri Kosina 2011-01-13 15:47:23 -08:00 committed by Linus Torvalds
parent 32d6feadf4
commit 5520e89485
1 changed files with 9 additions and 1 deletions
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10
mm/mmap.c
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@ -254,7 +254,15 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
down_write(&mm->mmap_sem);
#ifdef CONFIG_COMPAT_BRK
min_brk = mm->end_code;
/*
* CONFIG_COMPAT_BRK can still be overridden by setting
* randomize_va_space to 2, which will still cause mm->start_brk
* to be arbitrarily shifted
*/
if (mm->start_brk > PAGE_ALIGN(mm->end_data))
min_brk = mm->start_brk;
else
min_brk = mm->end_data;
#else
min_brk = mm->start_brk;
#endif