Re: [PATCH v2] audit: Report suspicious O_CREAT usage

Paul Moore
2019-10-02T21:12:16Z

On Tue, Oct 1, 2019 at 12:48 PM Kees Cook <keescook@chromium.org> wrote:
>
> This renames the very specific audit_log_link_denied() to
> audit_log_path_denied() and adds the AUDIT_* type as an argument. This
> allows for the creation of the new AUDIT_ANOM_CREAT that can be used to
> report the fifo/regular file creation restrictions that were introduced
> in commit 30aba6656f61 ("namei: allow restricted O_CREAT of FIFOs and
> regular files"). Additionally further clarifies the existing
> "operations" strings.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2:
> - fix build failure typo in CONFIG_AUDIT=n case
> - improve operations naming (paul)
> ---
> fs/namei.c | 8 ++++++--
> include/linux/audit.h | 5 +++--
> include/uapi/linux/audit.h | 1 +
> kernel/audit.c | 11 ++++++-----
> 4 files changed, 16 insertions(+), 9 deletions(-)

Thanks for the update, but I think we need another respin, see below.

> diff --git a/fs/namei.c b/fs/namei.c
> index 671c3c1a3425..2d5d245ae723 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -925,7 +925,7 @@ static inline int may_follow_link(struct nameidata *nd)
> return -ECHILD;
>
> audit_inode(nd->name, nd->stack[0].link.dentry, 0);
> - audit_log_link_denied("follow_link");
> + audit_log_path_denied(AUDIT_ANOM_LINK, "sticky_follow_link");

Maybe I should have been more clear in the last patch thread, but my
suggested name change was only for the new records you are adding; we
don't want to change the operation/op names for existing records. In
the above change, "follow_link" should stay "follow_link".

> @@ -993,7 +993,7 @@ static int may_linkat(struct path *link)
> if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
> return 0;
>
> - audit_log_link_denied("linkat");
> + audit_log_path_denied(AUDIT_ANOM_LINK, "unowned_linkat");

See above, this should stay as "linkat".

> @@ -1031,6 +1031,10 @@ static int may_create_in_sticky(struct dentry * const dir,
> (dir->d_inode->i_mode & 0020 &&
> ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
> (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
> + const char *operation = S_ISFIFO(inode->i_mode) ?
> + "sticky_create_fifo" :
> + "sticky_create_regular";
> + audit_log_path_denied(AUDIT_ANOM_CREAT, operation);

This is a new record, so this is fine. Thanks for changing this.

--
paul moore