RE: sctp: kernel memory overwrite attempt detected in sctp_getsockopt_assoc_stats

From: Dmitry Vyukov

Sent: 16 January 2017 14:04

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I've enabled CONFIG_HARDENED_USERCOPY_PAGESPAN on syzkaller fuzzer and

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The code also takes into account compound pages. As far as I
understand the intention of the check is to effectively find
out-of-bounds copies (e.g. goes beyond the current heap allocation). I
would expect that stacks are allocated as compound pages and don't
trigger this check. I don't see it is firing in other similar places.

Honestly, I'm not overly familiar with stack page allocation, at least not so
far as compound vs. single page allocation is concerned.  I suppose the question
your really asking here is: Have you found a case in which the syscall fuzzer
has forced the allocation of an insecure non-compound page on the stack, or is
this a false positive warning.  I can't provide the answer to that.

Yes. I added Kees, author of CONFIG_HARDENED_USERCOPY_PAGESPAN, to To line.
Kees, is this a false positive?

I'd guess that the kernel stack is (somehow) allocated page by page
rather than by a single multi-page allocate.
Or maybe vmalloc() isn't setting the required flag??

	David