Re: [PATCH] bpf, x32: Fix bug for BPF_JMP | {BPF_JSGT, BPF_JSLE, BPF_JSLT, BPF_JSGE}

[Greg KH <greg@kroah.com>]

On Thu, Nov 21, 2019 at 10:43:28AM +0100, Daniel Borkmann wrote:
> On 11/21/19 8:43 AM, Wang YanQing wrote:
> > commit 711aef1bbf88212a21f7103e88f397b47a528805 upstream.
> > 
> > The current method to compare 64-bit numbers for conditional jump is:
> > 
> > 1) Compare the high 32-bit first.
> > 
> > 2) If the high 32-bit isn't the same, then goto step 4.
> > 
> > 3) Compare the low 32-bit.
> > 
> > 4) Check the desired condition.
> > 
> > This method is right for unsigned comparison, but it is buggy for signed
> > comparison, because it does signed comparison for low 32-bit too.
> > 
> > There is only one sign bit in 64-bit number, that is the MSB in the 64-bit
> > number, it is wrong to treat low 32-bit as signed number and do the signed
> > comparison for it.
> > 
> > This patch fixes the bug.
> > 
> > Note:
> > The original commit adds a testcase in selftests/bpf for such bug, this
> > backport patch doesn't include the testcase, because the testcase needs
> > another upstream commit.
> > 
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=205469
> > Reported-by: Tony Ambardar <itugrok@yahoo.com>
> > Cc: Tony Ambardar <itugrok@yahoo.com>
> > Cc: stable@vger.kernel.org #v4.19
> > Signed-off-by: Wang YanQing <udknight@gmail.com>
> > Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> 
> Thanks a lot for backporting & testing, Wang, much appreciated! Greg, if you get a
> chance, please queue this & the other stable requests from Wang up.

All now queued up, thanks.

greg k-h