On Mon, Dec 6, 2021 at 4:12 AM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> On Wed, Dec 1, 2021 at 10:35 PM Bernard Zhao <bernard@xxxxxxxx> wrote:
> >
> > This patch try to fix potential memleak in function
> > selinux_fs_context_dup`s error branch.
> >
> > Signed-off-by: Bernard Zhao <bernard@xxxxxxxx>
> > ---
> > security/selinux/hooks.c | 22 ++++++++++++++++++----
> > 1 file changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 62d30c0a30c2..36d7fc373839 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -2856,24 +2856,38 @@ static int selinux_fs_context_dup(struct fs_context *fc,
> > if (src->fscontext) {
> > opts->fscontext = kstrdup(src->fscontext, GFP_KERNEL);
> > if (!opts->fscontext)
> > - return -ENOMEM;
> > + goto err_fscontext;
> > }
> > if (src->context) {
> > opts->context = kstrdup(src->context, GFP_KERNEL);
> > if (!opts->context)
> > - return -ENOMEM;
> > + goto err_context;
> > }
> > if (src->rootcontext) {
> > opts->rootcontext = kstrdup(src->rootcontext, GFP_KERNEL);
> > if (!opts->rootcontext)
> > - return -ENOMEM;
> > + goto err_rootcontext;
> > }
> > if (src->defcontext) {
> > opts->defcontext = kstrdup(src->defcontext, GFP_KERNEL);
> > if (!opts->defcontext)
> > - return -ENOMEM;
> > + goto err_defcontext;
> > }
> > return 0;
> > +
> > +err_defcontext:
> > + if (src->rootcontext)
> > + kfree(opts->rootcontext);
> > +err_rootcontext:
> > + if (src->context)
> > + kfree(opts->context);
> > +err_context:
> > + if (src->fscontext)
> > + kfree(opts->fscontext);
> > +err_fscontext:
> > + kfree(fc->security);
Also here you need to be careful to not double-free fc->security.
(Paul's pseudocode below already correctly resets it to NULL after
freeing.)
> > +
> > + return -ENOMEM;
> > }
>
> Thanks for catching this a providing a patch, however I think the
> memory cleanup can be made simpler, see the pseudo code below:
>
> static int selinux_fs_context_dup(...)
> {
>
> fc->security = kzalloc(...);
> if (!fc->security)
> return -ENOMEM;
>
> opts = fc->security;
>
> if (src->fscontext) {
> opts->fscontext = kstrdup(...);
> if (!opts->fscontext)
> goto err;
> }
>
> /* ... */
>
> return 0;
>
> err:
> kfree(opts->fscontext);
> kfree(opts->context);
> kfree(opts->rootcontext);
> kfree(opts->defcontext);
> kfree(opts);
> fc->security = NULL;
> return -ENOMEM;
> }
>
> --
> paul moore
> www.paul-moore.com
>
--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.
