On Thu, 28 Apr 2016 21:04:18 +0200 Mathias Krause <mini...@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().
Also, if this is indeed our design then
a) the various create_*_tables() should have comments in there which
explain this subtlety to the reader. Or, better, they use a common
helper function for this readiness-signaling operation because..
b) we'll need some barriers there to ensure that the environ_read()
caller sees the create_*_tables() writes in the correct order.
> 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.
