Messages in this thread | | | Date | Fri, 29 Apr 2016 07:59:00 +0200 | Subject | Re: [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready | From | Mathias Krause <> |
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On 28 April 2016 at 23:26, Andrew Morton <akpm@linux-foundation.org> wrote: > On Thu, 28 Apr 2016 21:04:18 +0200 Mathias Krause <minipli@googlemail.com> wrote: > >> If /proc/<PID>/environ gets read before the envp[] array is fully set >> up in create_{aout,elf,elf_fdpic,flat}_tables(), we might end up trying >> to read more bytes than are actually written, as env_start will already >> be set but env_end will still be zero, making the range calculation >> underflow, allowing to read beyond the end of what has been written. >> >> Fix this as it is done for /proc/<PID>/cmdline by testing env_end for >> zero. It is, apparently, intentionally set last in create_*_tables(). >> >> This bug was found by the PaX size_overflow plugin that detected the >> arithmetic underflow of 'this_len = env_end - (env_start + src)' when >> env_end is still zero. > > So what are the implications of this? From my reading, a craftily > constructed application could occasionally read arbitrarily large > amounts of kernel memory?
I don't think access_remote_vm() is capable of that. So, the only consequence is, userland trying to access /proc/<PID>/environ of a not yet fully set up process may get inconsistent data as we're in the middle of copying in the environment variables.
Regards, Mathias
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