linux-kernel - Re: [PATCH v2 1/6] LSM: Ensure the correct LSM context releaser

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Message-ID: <dad74779768e7c00d2a3c9bf8c60045d@paul-moore.com>
Date: Mon, 21 Oct 2024 19:39:48 -0400
From: Paul Moore <paul@...l-moore.com>
To: Casey Schaufler <casey@...aufler-ca.com>, casey@...aufler-ca.com, linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org, john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp, stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org, selinux@...r.kernel.org, mic@...ikod.net, linux-integrity@...r.kernel.org, netdev@...r.kernel.org, audit@...r.kernel.org, netfilter-devel@...r.kernel.org, linux-nfs@...r.kernel.org, Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH v2 1/6] LSM: Ensure the correct LSM context releaser

On Oct 14, 2024 Casey Schaufler <casey@...aufler-ca.com> wrote:
> 
> Add a new lsm_context data structure to hold all the information about a
> "security context", including the string, its size and which LSM allocated
> the string. The allocation information is necessary because LSMs have
> different policies regarding the lifecycle of these strings. SELinux
> allocates and destroys them on each use, whereas Smack provides a pointer
> to an entry in a list that never goes away.
> 
> Update security_release_secctx() to use the lsm_context instead of a
> (char *, len) pair. Change its callers to do likewise.  The LSMs
> supporting this hook have had comments added to remind the developer
> that there is more work to be done.
> 
> The BPF security module provides all LSM hooks. While there has yet to
> be a known instance of a BPF configuration that uses security contexts,
> the possibility is real. In the existing implementation there is
> potential for multiple frees in that case.
> 
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> Cc: linux-integrity@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Cc: audit@...r.kernel.org
> Cc: netfilter-devel@...r.kernel.org
> To: Pablo Neira Ayuso <pablo@...filter.org>
> Cc: linux-nfs@...r.kernel.org
> Cc: Todd Kjos <tkjos@...gle.com>
> Reviewed-by: Serge Hallyn <sergeh@...nel.org>
> ---
>  drivers/android/binder.c                | 24 ++++++-------
>  fs/ceph/xattr.c                         |  6 +++-
>  fs/nfs/nfs4proc.c                       |  8 +++--
>  fs/nfsd/nfs4xdr.c                       |  8 +++--
>  include/linux/lsm_hook_defs.h           |  2 +-
>  include/linux/security.h                | 35 +++++++++++++++++--
>  include/net/scm.h                       | 11 +++---
>  kernel/audit.c                          | 30 ++++++++---------
>  kernel/auditsc.c                        | 23 +++++++------
>  net/ipv4/ip_sockglue.c                  | 10 +++---
>  net/netfilter/nf_conntrack_netlink.c    | 10 +++---
>  net/netfilter/nf_conntrack_standalone.c |  9 +++--
>  net/netfilter/nfnetlink_queue.c         | 13 ++++---
>  net/netlabel/netlabel_unlabeled.c       | 45 +++++++++++--------------
>  net/netlabel/netlabel_user.c            | 11 +++---
>  security/apparmor/include/secid.h       |  2 +-
>  security/apparmor/secid.c               | 11 ++++--
>  security/security.c                     |  8 ++---
>  security/selinux/hooks.c                | 11 ++++--
>  19 files changed, 167 insertions(+), 110 deletions(-)

...

> diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
> index 1bc2d0890a9f..8303bbcfc543 100644
> --- a/net/netlabel/netlabel_unlabeled.c
> +++ b/net/netlabel/netlabel_unlabeled.c
> @@ -1127,14 +1122,14 @@ static int netlbl_unlabel_staticlist_gen(u32 cmd,
>  		secid = addr6->secid;
>  	}
>  
> -	ret_val = security_secid_to_secctx(secid, &secctx, &secctx_len);
> +	ret_val = security_secid_to_secctx(secid, &ctx.context, &ctx.len);
>  	if (ret_val != 0)
>  		goto list_cb_failure;
>  	ret_val = nla_put(cb_arg->skb,
>  			  NLBL_UNLABEL_A_SECCTX,
> -			  secctx_len,
> -			  secctx);
> -	security_release_secctx(secctx, secctx_len);
> +			  ctx.len,
> +			  ctx.context);

Nitpicky alignment issue; please keep the arguments aligned as they
are currently.

> +	security_release_secctx(&ctx);
>  	if (ret_val != 0)
>  		goto list_cb_failure;
>  

--
paul-moore.com