Re: [LKP] 4ce5f9c9e7 [ 1.323881] WARNING: CPU: 0 PID: 1 at mm/slab_common.c:1031 kmalloc_slab

Sean Christopherson
2018-10-11T00:31:44Z

On Wed, Oct 10, 2018 at 04:41:48PM -0700, Sean Christopherson wrote:
> On Wed, Oct 10, 2018 at 05:06:52PM -0500, Eric W. Biederman wrote:
> > ebiederm@xmission.com (Eric W. Biederman) writes:
> >
> > > So I am flummoxed. I am reading through the code and I don't see
> > > anything that could trigger this, and when I ran the supplied reproducer
> > > it did not reproduce for me.
> >
> > Even more so. With my tool chain the line that reports the failing
> > address is impossible.
> >
> > [ 73.034423] RIP: 0010:copy_siginfo_from_user+0x4d/0xd0
> >
> > With the supplied configureation my tool chain only has 0x30 bytes for
> > all of copy_siginfo_from_user. So I can't even begin to guess where
> > in that function things are failing.
> >
> > Any additional information that you can provide would be a real help
> > in tracking down this strange failure.
>
> I don't have the exact toolchain, but I was able to get somewhat close
> and may have found a smoking gun. 0x4d in my build is in the general
> vicinity of "sig_sicodes[sig].limit" in known_siginfo_layout(). This
> lines up with the register state from the log, e.g. RDI=0500104d8,
> which is the mask generated by sig_specific_sicodes. From what I can
> tell, @sig is never bounds checked. If the compiler generated an AND
> instruction to compare against sig_specific_sicodes then that could
> resolve true with any arbitrary value that happened to collide with
> sig_specific_sicodes and result in an out-of-bounds access to
> @sig_sicodes. siginfo_layout() for example explicitly checks @sig
> before indexing @sig_sicode, e.g. "sig < ARRAY_SIZE(sig_sicodes)".

Hmm, siginmask explicitly checks sig < SIGRTMIN, which might squash
my theory.

>
> Maybe this?
>
> ---
> kernel/signal.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 1c2dd117fee0..6ee7491de906 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2865,7 +2865,8 @@ static bool known_siginfo_layout(int sig, int si_code)
> if (si_code == SI_KERNEL)
> return true;
> else if ((si_code > SI_USER)) {
> - if (sig_specific_sicodes(sig)) {
> + if (sig < ARRAY_SIZE(sig_sicodes) &&
> + sig_specific_sicodes(sig)) {
> if (si_code <= sig_sicodes[sig].limit)
> return true;
> }