Re: [PATCH 1/1] file capabilities: clear fcaps on inode change (v2)

From: Stephen Smalley
Date: Tue Aug 07 2007 - 09:59:08 EST


On Mon, 2007-08-06 at 13:52 -0500, Serge E. Hallyn wrote:
> >From 1376764cbb54243f088cf00c39000c4f4418f461 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@xxxxxxxxxx>
> Date: Mon, 6 Aug 2007 14:20:06 -0400
> Subject: [PATCH 1/1] file capabilities: clear fcaps on inode change (v2)
>
> When a file with posix capabilities is overwritten, the
> file capabilities, like a setuid bit, should be removed.
>
> This patch introduces security_inode_killpriv(). This is
> currently only defined for capability, and is called when
> an inode is changed to inform the security module that
> it may want to clear out any privilege attached to that inode.
> The capability module checks whether any file capabilities
> are defined for the inode, and, if so, clears them.
>
> Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
> ---
> fs/attr.c | 7 +++++++
> fs/nfsd/vfs.c | 4 ++--
> fs/open.c | 3 ++-
> fs/splice.c | 4 ++++
> include/linux/fs.h | 1 +
> include/linux/security.h | 18 ++++++++++++++++++
> mm/filemap.c | 5 +++++
> security/capability.c | 1 +
> security/commoncap.c | 27 +++++++++++++++++++++++++++
> security/dummy.c | 6 ++++++
> security/security.c | 5 +++++
> 11 files changed, 78 insertions(+), 3 deletions(-)
>

> diff --git a/security/capability.c b/security/capability.c
> index dc2b66c..e23864e 100644
> --- a/security/capability.c
> +++ b/security/capability.c
> @@ -37,6 +37,7 @@ static struct security_operations capability_ops = {
>
> .inode_setxattr = cap_inode_setxattr,
> .inode_removexattr = cap_inode_removexattr,
> + .inode_removexattr = cap_inode_killpriv,

s/inode_removexattr/inode_killpriv/

Also, doesn't SELinux then need to define a corresponding hook function
to call the secondary module? Otherwise, it will fall back to the dummy
implementation and stacking selinux + capabilities with file caps won't
yield the right behavior.

--
Stephen Smalley
National Security Agency

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