Re: [RFC PATCH ghak21 4/4] audit: add parent of refused symlink to audit_names
On 2018-03-08 19:50, Paul Moore wrote:
On Wed, Feb 14, 2018 at 11:18 AM, Richard Guy Briggs
<rgb(a)redhat.com> wrote:
> Audit link denied events for symlinks were missing the parent PATH
> record. Add it. Since the full pathname may not be available,
> reconstruct it from the path in the nameidata supplied.
>
> See: https://github.com/linux-audit/audit-kernel/issues/21
> Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
> ---
> fs/namei.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 0edf133..bf1c046b 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -923,6 +923,7 @@ static inline int may_follow_link(struct nameidata *nd)
> const struct inode *inode;
> const struct inode *parent;
> kuid_t puid;
> + char *pathname;
>
> if (!sysctl_protected_symlinks)
> return 0;
> @@ -945,6 +946,14 @@ static inline int may_follow_link(struct nameidata *nd)
> if (nd->flags & LOOKUP_RCU)
> return -ECHILD;
>
> + pathname = kmalloc(PATH_MAX + 1, GFP_KERNEL);
> + if (!pathname)
> + return -ENOMEM;
Two things here:
1. We need to allocate a buffer to feed to d_absolute_path(), and
getname_kernel() is just going to make another copy so we need to make
sure we clean up after ourselves. Perhaps I missing it, but I'm not
seeing where we free the kmalloc'd buffer or call putname(). Feel
free to correct me if I'm missing something obvious.
That is put very diplomatically! Both fixed, with audit_panic() as
needed.
2. While the audit_* calls are going to bail early in the cases
where
audit is disabled, or not configured, we are going to pay the penalty
for the kmalloc() call above, as well as the getname_kernel() and
d_absolute_path() calls below. I think it might be beneficial to
create a new function (audit_log_symlink_denied() perhaps?) which
encapsulates all the audit bits in may_follow_link() and exits early
when needed. What do you think?
I agree a seperate function is appropriate. There was some back and
forth between namei.c and audit.c due to struct nameidata and
audit_panic() not able to co-exist due to them both being local to their
respective sub-systems.
(Point #2 is why I didn't merge patch 3/4, just include it in
this
revised patch)
On reviewing this, I'm not totally convinced the parent record is
necessary to fully understand what happenned since there is a CWD
record. I left 3 and 4 as seperate patches in case it is found that
only 3 is necessary.
> +
audit_inode(getname_kernel(d_absolute_path(&nd->stack[0].link, pathname,
> + PATH_MAX + 1)),
> + nd->stack[0].link.dentry, 0);
> + audit_inode(nd->name, nd->stack[0].link.dentry->d_parent,
LOOKUP_PARENT);
> +
> audit_inode(nd->name, nd->stack[0].link.dentry, 0);
> audit_log_link_denied("follow_link", &nd->stack[0].link);
>
> return -EACCES;
> --
> 1.8.3.1
--
paul moore
www.paul-moore.com
- RGB
--
Richard Guy Briggs <rgb(a)redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635