Messages in this thread Patch in this message | | | Date | Mon, 18 Jul 2016 11:45:53 -0400 (EDT) | From | Nicolas Pitre <> | Subject | Re: [PATCH v2 10/10] binfmt_flat: allow compressed flat binary format to work on MMU systems |
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On Mon, 18 Jul 2016, One Thousand Gnomes wrote:
> On Sun, 17 Jul 2016 23:31:56 -0400 > Nicolas Pitre <nicolas.pitre@linaro.org> wrote: > > > Let's take the simple and obvious approach by decompressing the binary > > into a kernel buffer and then copying it to user space. Those who are > > looking for more performance on a MMU system are unlikely to choose this > > executable format anyway. > > The flat loader takes a very casual attitude to overruns and corrupted > binaries. It's after all MMUless so has no real security model. If you > enable flat for an MMU system then IMHO those all need to be fixed > including all the missing overflow checks on the maths on textlen and the > like.
What about the following patch? This with existing user accessors and allocation error checks should cover it all.
----- >8 commit cc1051c9c57202772568600e96b75229a2a7cf19 Author: Nicolas Pitre <nicolas.pitre@linaro.org> Date: Mon Jul 18 11:28:57 2016 -0400
binfmt_flat: prevent kernel dammage from corrupted executable headers Signed-off-by: Nicolas Pitre <nico@linaro.org>
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c index 24deae4dcb..fa0054c1c3 100644 --- a/fs/binfmt_flat.c +++ b/fs/binfmt_flat.c @@ -498,6 +498,17 @@ static int load_flat_file(struct linux_binprm * bprm, } /* + * Make sure the header params are sane. + * 28 bits (256 MB) is way more than reasonable in this case. + * If some top bits are set we have probable binary corruption. + */ + if ((text_len | data_len | bss_len | stack_len | full_data) >> 28) { + printk("BINFMT_FLAT: bad header\n"); + ret = -ENOEXEC; + goto err; + } + + /* * fix up the flags for the older format, there were all kinds * of endian hacks, this only works for the simple cases */
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