selinux: fix another double free

Commit Message

Tom Rix June 11, 2020, 3:58 p.m. UTC

From: Tom Rix <[e-mail]>

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 <[e-mail]>
---
 security/selinux/ss/conditional.c | 1 -
 1 file changed, 1 deletion(-)

Comments

Stephen Smalley June 11, 2020, 4:36 p.m. UTC | #1

On Thu, Jun 11, 2020 at 11:58 AM <[e-mail]> wrote:
>
> From: Tom Rix <[e-mail]>
>
> 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 <[e-mail]>

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

Acked-by: Stephen Smalley <[e-mail]>

Ondrej Mosnacek June 11, 2020, 5:12 p.m. UTC | #2

Hi Tom,

On Thu, Jun 11, 2020 at 5:58 PM <[e-mail]> wrote:
> From: Tom Rix <[e-mail]>
>
> 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 <[e-mail]>
> ---
>  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,

Patch

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;
 }