Re: [PATCH -next] selinux: Fix potential memory leak in selinux_add_opt

[xiujianfeng]

在 2022/6/15 9:17, Paul Moore 写道:
> On Mon, Jun 13, 2022 at 9:18 PM xiujianfeng <xiujianfeng@xxxxxxxxxx> wrote:
> > 在 2022/6/14 4:22, Paul Moore 写道:
> > > On Sat, Jun 11, 2022 at 5:07 AM Xiu Jianfeng <xiujianfeng@xxxxxxxxxx> wrote:
> > > > In the entry of selinux_add_opt, *mnt_opts may be assigned to new
> > > > allocated memory, and also may be freed and reset at the end of the
> > > > function. however, if security_context_str_to_sid failed, it returns
> > > > directly and skips the procedure for free and reset, even if it may be
> > > > handled at the caller of this function, It is better to handle it
> > > > inside.
> > > >
> > > > Fixes: 70f4169ab421 ("selinux: parse contexts for mount options early")
> > > > Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
> > > > ---
> > > >    security/selinux/hooks.c | 12 +++++++-----
> > > >    1 file changed, 7 insertions(+), 5 deletions(-)
> > > Have you actually observed a memory leak from the selinux_mnt_opts
> > > allocation in selinux_add_opt()?
> > >
> > > The selinux_add_opt() function has two callers:
> > > selinux_sb_eat_lsm_opts() and selinux_fs_context_parse_param().  The
> > > former cleans up the selinux_mnt_opts allocation it its error handler
> > > while the latter will end up calling
> > > security_free_mnt_opts()/selinux_free_mnt_opts() to free the
> > > fs_context:security when the fs_context is destroyed.
> > >
> > > This patch shouldn't be necessary.
> > I may not have made it clear, I said potential means may have a third
> > caller in the future.
> Let's not worry about it.  If you wanted to add a comment header to
> the function (see selinux_skb_peerlbl_sid() for an example) to make it
> clear that callers are responsible for cleaning up @mnt_opts on error
> I think that would be okay ... although even that is going to be a
> problem in the new mount API case where selinux_add_opt() is going to
> be called multiple times.
>
> > I think the error handler as following is not necessary:
> >
> > err:
> >           if (is_alloc_opts) {
> >                   kfree(opts);
> >                   *mnt_opts = NULL;
> >           }
> >
> > otherwise, some error paths goto err label while others don't, It's
> > confusing.
> That's a fair point.  Looking at the patch which added it, we should
> probably also return EINVAL when @s is NULL instead of ENOMEM.  In
> fact, in all the cases where we currently jump to @err, I think we are
> guaranteed that @is_alloc_opts is false as it requires a previously
> populated @opts.
>
> If you want to submit another patch, I would suggest doing the
> following in the patch:
>
> 1. Change the @s NULL check to return -EINVAL when @s is NULL.
> 2. Allocate @opts/@mnt_opts if NULL, but don't call kfree() on the
> object in case of error.  The new mount API will cleanup when it is
> done and selinux_sb_eat_lsm_opts() will cleanup on error.
>
> If you don't have time to put together a patch for this, let me know and I will.

no problem, I will do it, thanks for your suggestion.

>