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SubjectRe: [PATCH v2 2/3] exec: kill "int depth" in search_binary_handler()
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On Sat, Aug 3, 2013 at 11:55 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 08/03, Kees Cook wrote:
>>
>> On Thu, Aug 1, 2013 at 12:05 PM, Oleg Nesterov <oleg@redhat.com> wrote:
>> > Nobody except search_binary_handler() should touch ->recursion_depth,
>> > "int depth" buys nothing but complicates the code, kill it.
>>
>> I'd like to see a comment added to binfmts.h's recursion_depth field
>> that reminds people that recursion_depth is for
>> search_binary_handler()'s use only, and a binfmt loader shouldn't
>> touch it.
>
> And this comment probably makes sense even without this change

Yeah totally agreed -- I should have added this when I reorganized the
depth handling earlier. :)

>> Besides that, yeah, sensible clean up.
>
> OK, thanks, please see v2. The only change is the comment in .h
>
> ------------------------------------------------------------------------------
> Subject: [PATCH 1/1] exec: kill "int depth" in search_binary_handler()
>
> Nobody except search_binary_handler() should touch ->recursion_depth,
> "int depth" buys nothing but complicates the code, kill it.
>
> Probably we should also kill "fn" and the !NULL check, ->load_binary
> should be always defined. And it can not go away after read_unlock()
> or this code is buggy anyway.
>
> v2: add the comment about linux_binprm->recursion_depth
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Kees Cook <keescook@chromium.org>

Thanks,

-Kees

> ---
> fs/exec.c | 9 ++++-----
> include/linux/binfmts.h | 2 +-
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index a9ae4f2..f32079c 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1370,12 +1370,11 @@ EXPORT_SYMBOL(remove_arg_zero);
> */
> int search_binary_handler(struct linux_binprm *bprm)
> {
> - unsigned int depth = bprm->recursion_depth;
> - int try,retval;
> + int try, retval;
> struct linux_binfmt *fmt;
>
> /* This allows 4 levels of binfmt rewrites before failing hard. */
> - if (depth > 5)
> + if (bprm->recursion_depth > 5)
> return -ELOOP;
>
> retval = security_bprm_check(bprm);
> @@ -1396,9 +1395,9 @@ int search_binary_handler(struct linux_binprm *bprm)
> if (!try_module_get(fmt->module))
> continue;
> read_unlock(&binfmt_lock);
> - bprm->recursion_depth = depth + 1;
> + bprm->recursion_depth++;
> retval = fn(bprm);
> - bprm->recursion_depth = depth;
> + bprm->recursion_depth--;
> if (retval >= 0) {
> put_binfmt(fmt);
> allow_write_access(bprm->file);
> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
> index 70cf138..e8112ae 100644
> --- a/include/linux/binfmts.h
> +++ b/include/linux/binfmts.h
> @@ -31,7 +31,7 @@ struct linux_binprm {
> #ifdef __alpha__
> unsigned int taso:1;
> #endif
> - unsigned int recursion_depth;
> + unsigned int recursion_depth; /* only for search_binary_handler() */
> struct file * file;
> struct cred *cred; /* new credentials */
> int unsafe; /* how unsafe this exec is (mask of LSM_UNSAFE_*) */
> --
> 1.5.5.1
>
>



--
Kees Cook
Chrome OS Security


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