[RFC PATCH 2/2] selinux: fall back to ref-walk upon LSM_AUDIT_DATA_DENTRY too

[Paul Moore]

On Thu, Nov 21, 2019 at 9:52 AM Stephen Smalley <sds at tycho.nsa.gov> wrote:
> commit bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
> passed down the rcu flag to the SELinux AVC, but failed to adjust the
> test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY.
> Previously, we only returned -ECHILD if generating an audit record with
> LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission.
> Return -ECHILD on either LSM_AUDIT_DATA_INODE or LSM_AUDIT_DATA_DENTRY.
> LSM_AUDIT_DATA_INODE only requires this handling due to the fact
> that dump_common_audit_data() calls d_find_alias() and collects the
> dname from the result if any.
> Other cases that might require similar treatment in the future are
> LSM_AUDIT_DATA_PATH and LSM_AUDIT_DATA_FILE if any hook that takes
> a path or file is called under RCU-walk.
>
> Fixes: bda0be7ad994 ("security: make inode_follow_link RCU-walk aware")
> Signed-off-by: Stephen Smalley <sds at tycho.nsa.gov>
> ---
>  security/selinux/avc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/security/selinux/avc.c b/security/selinux/avc.c
> index 74c43ebe34bb..f1fa1072230c 100644
> --- a/security/selinux/avc.c
> +++ b/security/selinux/avc.c
> @@ -779,7 +779,8 @@ noinline int slow_avc_audit(struct selinux_state *state,
>          * during retry. However this is logically just as if the operation
>          * happened a little later.
>          */
> -       if ((a->type == LSM_AUDIT_DATA_INODE) &&
> +       if ((a->type == LSM_AUDIT_DATA_INODE ||
> +            a->type == LSM_AUDIT_DATA_DENTRY) &&
>             (flags & MAY_NOT_BLOCK))
>                 return -ECHILD;

Added the LSM list as I'm beginning to wonder if we should push this
logic down into common_lsm_audit(), this problem around blocking
shouldn't be SELinux specific.

For the LSM folks just joining, the full patchset can be found here:
* https://lore.kernel.org/selinux/20191121145245.8637-1-sds@tycho.nsa.gov/T/#t

-- 
paul moore
www.paul-moore.com