Messages in this thread | | | Date | Wed, 10 Oct 2018 17:31:42 -0700 | From | Sean Christopherson <> | Subject | Re: [LKP] 4ce5f9c9e7 [ 1.323881] WARNING: CPU: 0 PID: 1 at mm/slab_common.c:1031 kmalloc_slab |
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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; > }
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