[PATCH] selinux: fix another double free

[PATCH] selinux: fix another double free

[trix]

From: Tom Rix <trix@redhat.com>

Clang static analysis reports this double free error

security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
        kfree(node->expr.nodes);
        ^~~~~~~~~~~~~~~~~~~~~~~

When cond_read_node fails, it calls cond_node_destroy which frees the
node but does not poison the entry in the node list.  So when it
returns to its caller cond_read_list, cond_read_list deletes the
partial list.  The latest entry in the list will be deleted twice.

So instead of freeing the node in cond_read_node, let list freeing in
code_read_list handle the freeing the problem node along with all of the the
earlier nodes.

Signed-off-by: Tom Rix <trix@redhat.com>
---
 security/selinux/ss/conditional.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
index da94a1b4bfda..ffb31af22f4f 100644
--- a/security/selinux/ss/conditional.c
+++ b/security/selinux/ss/conditional.c
@@ -411,7 +411,6 @@ static int cond_read_node(struct policydb *p, struct cond_node *node, void *fp)
 		goto err;
 	return 0;
 err:
-	cond_node_destroy(node);
 	return rc;
 }
 
-- 
2.18.1

Re: [PATCH] selinux: fix another double free

[Stephen Smalley]

On Thu, Jun 11, 2020 at 11:58 AM <trix@redhat.com> wrote:
>
> From: Tom Rix <trix@redhat.com>
>
> Clang static analysis reports this double free error
>
> security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
>         kfree(node->expr.nodes);
>         ^~~~~~~~~~~~~~~~~~~~~~~
>
> When cond_read_node fails, it calls cond_node_destroy which frees the
> node but does not poison the entry in the node list.  So when it
> returns to its caller cond_read_list, cond_read_list deletes the
> partial list.  The latest entry in the list will be deleted twice.
>
> So instead of freeing the node in cond_read_node, let list freeing in
> code_read_list handle the freeing the problem node along with all of the the
> earlier nodes.
>
> Signed-off-by: Tom Rix <trix@redhat.com>

Looks like this was introduced by
60abd3181db29ea81742106cc0ac2e27fd05b418 ("selinux: convert cond_list
to array").

Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>

Re: [PATCH] selinux: fix another double free

[Ondrej Mosnacek]

Hi Tom,

On Thu, Jun 11, 2020 at 5:58 PM <trix@redhat.com> wrote:
> From: Tom Rix <trix@redhat.com>
>
> Clang static analysis reports this double free error
>
> security/selinux/ss/conditional.c:139:2: warning: Attempt to free released memory [unix.Malloc]
>         kfree(node->expr.nodes);
>         ^~~~~~~~~~~~~~~~~~~~~~~
>
> When cond_read_node fails, it calls cond_node_destroy which frees the
> node but does not poison the entry in the node list.  So when it
> returns to its caller cond_read_list, cond_read_list deletes the
> partial list.  The latest entry in the list will be deleted twice.
>
> So instead of freeing the node in cond_read_node, let list freeing in
> code_read_list handle the freeing the problem node along with all of the the

There is an extra "the" before "freeing".

> earlier nodes.
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
>  security/selinux/ss/conditional.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
> index da94a1b4bfda..ffb31af22f4f 100644
> --- a/security/selinux/ss/conditional.c
> +++ b/security/selinux/ss/conditional.c
> @@ -411,7 +411,6 @@ static int cond_read_node(struct policydb *p, struct cond_node *node, void *fp)
>                 goto err;
>         return 0;
>  err:
> -       cond_node_destroy(node);
>         return rc;

Since there is now just "return rc" in the error path, can you please
replace all the gotos with plain return statements? And please also
add a Fixes: tag pointing to the commit that introduced the bug (see
Stephen's reply).

Thanks,

-- 
Ondrej Mosnacek
Software Engineer, Platform Security - SELinux kernel
Red Hat, Inc.