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>
diff --git a/mm/mmap.c b/mm/mmap.c
index 73cc648..2ec8eb5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -254,7 +254,15 @@
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
