| Message ID | alpine.DEB.2.20.1607181006190.9597@Yrabib |
|---|---|
| State | New |
| Headers | show |
On Mon, 18 Jul 2016, One Thousand Gnomes wrote: > On Mon, 18 Jul 2016 11:45:53 -0400 (EDT) > Nicolas Pitre <nicolas.pitre@linaro.org> wrote: > > > 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"); > > Apart from the printk that looks good for the header but I think the rest > could do with a fair bit more review (eg relocations in range checks). Given that they all go through put_user() now, the worst that could happen is an executable that craps onto itself. I don't think there is much we can do here besides letting the user task crash. Nicolas
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 */