Hi,
On Sun, Sep 12, 2021 at 2:23 PM Eugene Syromiatnikov <esyr@xxxxxxxxxx> wrote:
> Commit 2d151d39073a ("xfrm: Add possibility to set the default to block
> if we have no policy") broke ABI by changing the value of the XFRM_MSG_MAPPING
> enum item, thus also evading the build-time check
> in security/selinux/nlmsgtab.c:selinux_nlmsg_lookup for presence of proper
> security permission checks in nlmsg_xfrm_perms. Fix it by placing
> XFRM_MSG_SETDEFAULT/XFRM_MSG_GETDEFAULT to the end of the enum, right before
> __XFRM_MSG_MAX, and updating the nlmsg_xfrm_perms accordingly.
>
> Fixes: 2d151d39073a ("xfrm: Add possibility to set the default to block if we have no policy")
> References: https://lore.kernel.org/netdev/20210901151402.GA2557@xxxxxxxxxxxx/
> Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
> ---
> v2:
> - Updated SELinux nlmsg_xfrm_perms permissions table and selinux_nlmsg_lookup
> build-time check accordingly.
>
> v1: https://lore.kernel.org/lkml/20210901153407.GA20446@xxxxxxxxxxxxxxxxx/
> ---
> include/uapi/linux/xfrm.h | 6 +++---
> security/selinux/nlmsgtab.c | 4 +++-
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
> index b96c1ea..26f456b1 100644
> --- a/include/uapi/linux/xfrm.h
> +++ b/include/uapi/linux/xfrm.h
> @@ -213,13 +213,13 @@ enum {
> XFRM_MSG_GETSPDINFO,
> #define XFRM_MSG_GETSPDINFO XFRM_MSG_GETSPDINFO
>
> + XFRM_MSG_MAPPING,
> +#define XFRM_MSG_MAPPING XFRM_MSG_MAPPING
> +
> XFRM_MSG_SETDEFAULT,
> #define XFRM_MSG_SETDEFAULT XFRM_MSG_SETDEFAULT
> XFRM_MSG_GETDEFAULT,
> #define XFRM_MSG_GETDEFAULT XFRM_MSG_GETDEFAULT
> -
> - XFRM_MSG_MAPPING,
> -#define XFRM_MSG_MAPPING XFRM_MSG_MAPPING
Perhaps it would be a good idea to put a comment here to make it less
likely that this repeats in the future. Something like:
/* IMPORTANT: Only insert new entries right above this line, otherwise
you break ABI! */
> __XFRM_MSG_MAX
> };
> #define XFRM_MSG_MAX (__XFRM_MSG_MAX - 1)
> diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
> index d59276f..94ea2a8 100644
> --- a/security/selinux/nlmsgtab.c
> +++ b/security/selinux/nlmsgtab.c
> @@ -126,6 +126,8 @@ static const struct nlmsg_perm nlmsg_xfrm_perms[] =
> { XFRM_MSG_NEWSPDINFO, NETLINK_XFRM_SOCKET__NLMSG_WRITE },
> { XFRM_MSG_GETSPDINFO, NETLINK_XFRM_SOCKET__NLMSG_READ },
> { XFRM_MSG_MAPPING, NETLINK_XFRM_SOCKET__NLMSG_READ },
> + { XFRM_MSG_SETDEFAULT, NETLINK_XFRM_SOCKET__NLMSG_WRITE },
> + { XFRM_MSG_GETDEFAULT, NETLINK_XFRM_SOCKET__NLMSG_READ },
> };
>
> static const struct nlmsg_perm nlmsg_audit_perms[] =
> @@ -189,7 +191,7 @@ int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm)
> * structures at the top of this file with the new mappings
> * before updating the BUILD_BUG_ON() macro!
> */
> - BUILD_BUG_ON(XFRM_MSG_MAX != XFRM_MSG_MAPPING);
> + BUILD_BUG_ON(XFRM_MSG_MAX != XFRM_MSG_GETDEFAULT);
> err = nlmsg_perm(nlmsg_type, perm, nlmsg_xfrm_perms,
> sizeof(nlmsg_xfrm_perms));
> break;
> --
> 2.1.4
>
--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.
