Messages in this thread | | | Date | Wed, 24 Apr 2019 13:24:07 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] lkdtm: fix potential use after free |
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Hi,
On Wed, Apr 24, 2019 at 05:59:52PM +0800, Weikang shi wrote: > From: swkhack <swkhack@gmail.com> > > The function lkdtm_READ_AFTER_FREE calls kfree(base) to free the memory > of base. However, following kfree(base), > it access the memory which base point to via base[offset]. This may result in a > use-after-free bug.
This is deliberate; the test is designed to provoke a use-after-free to verify that this can be detected by tools such as KASAN.
> This patch moves kfree(base) after the dereference.
Doing this would break the test, so we should not make this change.
Was this something you spotted with a static analysis tool?
> Signed-off-by: swkhack <swkhack@gmail.com>
A signed-off-by line should have your real name rather than an alias.
Thanks, Mark.
> --- > drivers/misc/lkdtm/heap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c > index 65026d7de..3e2f1580a 100644 > --- a/drivers/misc/lkdtm/heap.c > +++ b/drivers/misc/lkdtm/heap.c > @@ -77,7 +77,6 @@ void lkdtm_READ_AFTER_FREE(void) > base[offset] = *val; > pr_info("Value in memory before free: %x\n", base[offset]); > > - kfree(base); > > pr_info("Attempting bad read from freed memory\n"); > saw = base[offset]; > @@ -88,6 +87,7 @@ void lkdtm_READ_AFTER_FREE(void) > } > pr_info("Memory was not poisoned\n"); > > + kfree(base); > kfree(val); > } > > -- > 2.17.1 >
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