On Fri, Dec 4, 2015 at 12:24 AM, Lee Jones [off-list ref] wrote:

On Thu, 03 Dec 2015, Arnd Bergmann wrote:

quoted

On Thursday 03 December 2015 17:28:30 Lee Jones wrote:

quoted

quoted

Ah, interesting. I haven't tried myself, and just tried to read the
code. Maybe glibc already catches zero-length writes before it gets
into the kernel, or I just missed the part of the syscall that checks
for this.

Glibc is responsible indeed:

  http://osxr.org/glibc/source/io/write.c

Ok, so an attacker can force the stack overflow by calling
syscall(__NR_write, fd, p, 0) if that has any potential value,
but normal users won't hit this case.

Right.  I have fixed the issue (and another one I found) anyway, if
only to rid the GCC warning.

Sorry, but I'm unable to find a new version of this patch, did I miss
it or could you resend it?


Also, as I looked at this again, we should probably return an error if
count >= sizeof(buf) rather than just acknowledging the input (same in
the other debugfs write function in this file).

Regards,
Bjorn