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authorJiri Kosina <jkosina@suse.cz>2011-01-13 15:47:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:48 -0800
commit5520e89485252c759ee60d313e9422447659947b (patch)
treecae55e5e44e86a19af4103ec129d887004d26b5b /mm/mmap.c
parent32d6feadf4e17ea9b98071be9bbf402a74a4f818 (diff)
downloadlwn-5520e89485252c759ee60d313e9422447659947b.tar.gz
lwn-5520e89485252c759ee60d313e9422447659947b.zip
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>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 73cc648873d6..2ec8eb5a9cdd 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -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