linux-kernel - Re: [PATCH v2] parisc: Fix ptrace syscall number modification

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Message-ID: <20190216224207.GA25554@altlinux.org>
Date:   Sun, 17 Feb 2019 01:42:07 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Helge Deller <deller@....de>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] parisc: Fix ptrace syscall number modification

On Sat, Feb 16, 2019 at 05:55:24PM +0100, Helge Deller wrote:
> On 16.02.19 14:10, Dmitry V. Levin wrote:
> > Commit 910cd32e552e ("parisc: Fix and enable seccomp filter support")
> > introduced a regression in ptrace-based syscall tampering: when tracer
> > changes syscall number to -1, the kernel fails to initialize %r28 with
> > -ENOSYS and subsequently fails to return the error code of the failed
> > syscall to userspace.
> > 
> > This erroneous behaviour could be observed with a simple strace syscall
> > fault injection command which is expected to print something like this:
> > 
> > $ strace -a0 -ewrite -einject=write:error=enospc echo hello
> > write(1, "hello\n", 6) = -1 ENOSPC (No space left on device) (INJECTED)
> > write(2, "echo: ", 6) = -1 ENOSPC (No space left on device) (INJECTED)
> > write(2, "write error", 11) = -1 ENOSPC (No space left on device) (INJECTED)
> > write(2, "\n", 1) = -1 ENOSPC (No space left on device) (INJECTED)
> > +++ exited with 1 +++
> > 
> > After commit 910cd32e552ea09caa89cdbe328e468979b030dd it loops printing
> > something like this instead:
> > 
> > write(1, "hello\n", 6../strace: Failed to tamper with process 12345: unexpectedly got no error (return value 0, error 0)
> > ) = 0 (INJECTED)
> > 
> > This bug was found by strace test suite.
> > 
> > Fixes: 910cd32e552e ("parisc: Fix and enable seccomp filter support")
> > Cc: stable@...r.kernel.org # v4.5+
> > Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
> 
> Thanks, the patch works as expected.
> You may add:
> Tested-by: Helge Deller <deller@....de>
> 
> There is an "out" label a few lines below, which should be removed as well.
> Otherwise you get this warning:
> arch/parisc/kernel/ptrace.c: In function ‘do_syscall_trace_enter’:
> arch/parisc/kernel/ptrace.c:357:1: warning: label ‘out’ defined but not used [-Wunused-label]
> 
> I've fixed it up locally and added the patch to my for-next tree.
> If it's ok for you, I'll push it through the parisc tree.

It's fine with me, thanks!


-- 
ldv

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