Messages in this thread | | | Date | Fri, 29 Apr 2016 13:25:24 +0300 | Subject | Re: [PATCH] proc: prevent accessing /proc/<PID>/environ until it's ready | From | Alexey Dobriyan <> |
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On Fri, Apr 29, 2016 at 9:02 AM, Mathias Krause <minipli@googlemail.com> wrote: > On 28 April 2016 at 23:30, 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(). >> >> 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. > > I totally agree that this kind of "synchronization" is rather fragile. > Adding comments won't help much, I fear. Rather a dedicated flag, > signaling "process ready for inspection" may be needed. So far, that's > what env_end is (ab-)used for.
If MM Cabal is OK with MMF_LOAD_BINARY_OK flag applied at search_binary_handler(), it should work for /proc .
Alexey
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