Re: [PATCH] audit: handle unknown status requests in audit_receive_msg

On Tue, Mar 3, 2026 at 7:42 AM Ricardo Robaina <[email protected]> wrote:
>
> Currently, audit_receive_msg() ignores unknown status bits in AUDIT_SET
> requests, incorrectly returning success to newer user space tools
> querying unsupported features. This breaks forward compatibility.
>
> Fix this by defining AUDIT_STATUS_ALL in the UAPI header and returning
> -EINVAL if any unrecognized bits are set (s.mask & ~AUDIT_STATUS_ALL).
> This ensures invalid requests are safely rejected, allowing user space
> to reliably test for and gracefully handle feature detection on older
> kernels.
>
> Suggested-by: Steve Grubb <[email protected]>
> Signed-off-by: Ricardo Robaina <[email protected]>
> ---
>  include/uapi/linux/audit.h | 9 +++++++++
>  kernel/audit.c             | 2 ++
>  2 files changed, 11 insertions(+)
>
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 14a1c1fe013a..1d5122b9274a 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -356,6 +356,15 @@ enum {
>  #define AUDIT_STATUS_LOST                      0x0040
>  #define AUDIT_STATUS_BACKLOG_WAIT_TIME_ACTUAL  0x0080
>
> +#define AUDIT_STATUS_ALL (AUDIT_STATUS_ENABLED | \
> +                         AUDIT_STATUS_FAILURE | \
> +                         AUDIT_STATUS_PID | \
> +                         AUDIT_STATUS_RATE_LIMIT | \
> +                         AUDIT_STATUS_BACKLOG_LIMIT | \
> +                         AUDIT_STATUS_BACKLOG_WAIT_TIME | \
> +                         AUDIT_STATUS_LOST | \
> +                         AUDIT_STATUS_BACKLOG_WAIT_TIME_ACTUAL)

Overall I think this is fine and good, but AUDIT_STATUS_ALL doesn't
need to be in the UAPI so why don't we move it to
include/linux/audit.h?  You can put it at the very top, right above
the AUDIT_INO_UNSET macro.

>  #define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT     0x00000001
>  #define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME 0x00000002
>  #define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH   0x00000004
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 5a0216056524..592383dce090 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1295,6 +1295,8 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
>                 memset(&s, 0, sizeof(s));
>                 /* guard against past and future API changes */
>                 memcpy(&s, data, min_t(size_t, sizeof(s), data_len));
> +               if (s.mask & ~AUDIT_STATUS_ALL)
> +                       return -EINVAL;
>                 if (s.mask & AUDIT_STATUS_ENABLED) {
>                         err = audit_set_enabled(s.enabled);
>                         if (err < 0)
> --
> 2.53.0

-- 
paul-moore.com