linux-kernel - Re: [PATCH ghak100 V2 1/2] audit: more filter PATH records keyed on filesystem magic

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Date:   Fri, 25 Jan 2019 16:36:53 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        Steve Grubb <sgrubb@...hat.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH ghak100 V2 1/2] audit: more filter PATH records keyed on
 filesystem magic

On Wed, Jan 23, 2019 at 1:35 PM Richard Guy Briggs <rgb@...hat.com> wrote:
> Like commit 42d5e37654e4 ("audit: filter PATH records keyed on
> filesystem magic") that addresses
> https://github.com/linux-audit/audit-kernel/issues/8
>
> Any user or remote filesystem could become unavailable and effectively
> block on a forced unmount.
>
>     -a always,exit -S umount2 -F key=umount2
>
> Provide a method to ignore these user and remote filesystems to prevent
> them from being impossible to unmount.
>
> Extend the "AUDIT_FILTER_FS" filter that uses the field type
> AUDIT_FSTYPE keying off the filesystem 4-octet hexadecimal magic
> identifier to filter specific filesystems to cover audit_inode() to address
> this blockage.
>
> An example rule would look like:
>     -a never,filesystem -F fstype=0x517B -F key=ignore_smb
>     -a never,filesystem -F fstype=0x6969 -F key=ignore_nfs
>
> Arguably the better way to address this issue is to disable auditing
> processes that touch removable filesystems.
>
> Note: refactor __audit_inode_child() to remove two levels of if
> indentation.
>
> Please see the github issue tracker
> https://github.com/linux-audit/audit-kernel/issues/100
>
> Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> ---
>  kernel/auditsc.c | 35 +++++++++++++++++++++++++++--------
>  1 file changed, 27 insertions(+), 8 deletions(-)

Thanks, merged.

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index b585ceb2f7a2..3d05d5fc6240 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1763,10 +1763,31 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
>         struct inode *inode = d_backing_inode(dentry);
>         struct audit_names *n;
>         bool parent = flags & AUDIT_INODE_PARENT;
> +       struct audit_entry *e;
> +       struct list_head *list = &audit_filter_list[AUDIT_FILTER_FS];
> +       int i;
>
>         if (!context->in_syscall)
>                 return;
>
> +       rcu_read_lock();
> +       if (!list_empty(list)) {
> +               list_for_each_entry_rcu(e, list, list) {
> +                       for (i = 0; i < e->rule.field_count; i++) {
> +                               struct audit_field *f = &e->rule.fields[i];
> +
> +                               if (f->type == AUDIT_FSTYPE
> +                                   && audit_comparator(inode->i_sb->s_magic,
> +                                                       f->op, f->val)
> +                                   && e->rule.action == AUDIT_NEVER) {
> +                                       rcu_read_unlock();
> +                                       return;
> +                               }
> +                       }
> +               }
> +       }
> +       rcu_read_unlock();
> +
>         if (!name)
>                 goto out_alloc;
>
> @@ -1875,14 +1896,12 @@ void __audit_inode_child(struct inode *parent,
>                         for (i = 0; i < e->rule.field_count; i++) {
>                                 struct audit_field *f = &e->rule.fields[i];
>
> -                               if (f->type == AUDIT_FSTYPE) {
> -                                       if (audit_comparator(parent->i_sb->s_magic,
> -                                           f->op, f->val)) {
> -                                               if (e->rule.action == AUDIT_NEVER) {
> -                                                       rcu_read_unlock();
> -                                                       return;
> -                                               }
> -                                       }
> +                               if (f->type == AUDIT_FSTYPE
> +                                   && audit_comparator(parent->i_sb->s_magic,
> +                                                       f->op, f->val)
> +                                   && e->rule.action == AUDIT_NEVER) {
> +                                       rcu_read_unlock();
> +                                       return;
>                                 }
>                         }
>                 }
> --
> 1.8.3.1
>


-- 
paul moore
www.paul-moore.com