Messages in this thread Patch in this message | | | Date | Wed, 10 Oct 2018 16:41:48 -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 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)".
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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