Messages in this thread Patch in this message |  | | | Date | Mon, 3 Jan 2011 14:24:12 +0100 (CET) | | From | Jiri Kosina <> | | Subject | [PATCH v2] brk: fix min_brk lower bound computation for COMPAT_BRK |
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> > diff --git a/mm/mmap.c b/mm/mmap.c > > index 50a4aa0..35d9f9c 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -253,7 +253,15 @@ 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 make mm->start_brk > > + * to be arbitrarily shifted > > + */ > > + if (mm->start_brk > mm->end_code) > > + min_brk = mm->start_brk; > > + else > > + min_brk = mm->end_code; > > #else > > min_brk = mm->start_brk; > > #endif > > Hmm, actually no, that will bring us back into pre-a5b4592c era, please > disregard that. > > I will have to come up with something more clever (we can't just check > 'randomize_va_space == 2', as that would be racy for already running > programs).
The patch below handles all the cases properly. Ingo, Andrew, please consider applying. Thanks.
From: Jiri Kosina <jkosina@suse.cz> Subject: [PATCH] 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).
Signed-off-by: Jiri Kosina <jkosina@suse.cz> --- mm/mmap.c | 10 +++++++++- 1 files changed, 9 insertions(+), 1 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 50a4aa0..ca2f164 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -253,7 +253,15 @@ 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 make 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 -- 1.7.3.1
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