On Wed, 2008-09-03 at 10:26 -0400, Eric Paris wrote:
> On Wed, 2008-09-03 at 10:08 -0400, Stephen Smalley wrote:
> > On Wed, 2008-09-03 at 09:58 -0400, Eric Paris wrote:
> > > Fix a bug and a philosophical decision about who handles errors.
> > >
> > > security_context_to_sid_core() was leaking a context in the common case.
> > > This was causing problems on fedora systems which recently have started
> > > making extensive use of this function.
> > >
> > > In discussion it was decided that if string_to_context_struct() had an
> > > error it was its own responsibility to clean up any mess it created
> > > along the way. Remember that it is perfectly safe to call
> > > context_destroy() on the same context twice and so this will not
> > > introduce any double frees or cause issues with the other change.
> >
> > Well, there are two possibilities. Either:
> > 1) we are fine with multiple calls to context_destroy(), in which case
> > the original patch stands as is, or
>
> I'm fine with it standing, but I rewrote it really because I didn't want
> yet another needless goto that I added.
>
> > 2) we want to avoid multiple calls to context_destroy(), in which case
> > this patch is still wrong - the latter context_destroy() call should
> > only occur _before_ the out label (i.e. same place it was, only without
> > the conditional).
>
> Lets go this route just to have some consistency. I put it where I did
> so it was done without the policy_rwlock. Since we are now seeing
> hundreds to thousands of calls to this code path I think its worth it to
> be a slight bit more picky with the locking. So how about a version 3
> like this? If you ack I'll send it cleanly for jmorris....
I'm not sure it is justified - we are only talking about a readlock
there, and centralizing the lock/unlock sequence seems generally good.
>
> ---
>
> security/selinux/ss/services.c | 12 +++++++-----
> 1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index b52f923..a0a73e7 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -811,11 +811,12 @@ static int string_to_context_struct(struct policydb *pol,
> /* Check the validity of the new context. */
> if (!policydb_context_isvalid(pol, ctx)) {
> rc = -EINVAL;
> - context_destroy(ctx);
> goto out;
> }
> rc = 0;
> out:
> + if (rc)
> + context_destroy(ctx);
> return rc;
> }
>
> @@ -865,13 +866,14 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len,
> context.str = str;
> context.len = scontext_len;
> str = NULL;
> - } else if (rc)
> + } else if (rc) {
> + read_unlock(&policy_rwlock);
> goto out;
> + }
> rc = sidtab_context_to_sid(&sidtab, &context, sid);
> - if (rc)
> - context_destroy(&context);
> -out:
> read_unlock(&policy_rwlock);
> + context_destroy(&context);
> +out:
> kfree(scontext2);
> kfree(str);
> return rc;
>
>
>
> --
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--
Stephen Smalley
National Security Agency
--
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