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Message-Id: <1183387015.12218.25.camel@moss-spartans.epoch.ncsc.mil>
Date: Mon, 02 Jul 2007 10:36:55 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: "Serge E. Hallyn" <serue@...ibm.com>
Cc: Andrew Morgan <morgan@...nel.org>,
Chris Wright <chrisw@...s-sol.org>,
Andrew Morgan <agm@...gle.com>, casey@...aufler-ca.com,
Andrew Morton <akpm@...gle.com>,
KaiGai Kohei <kaigai@...gai.gr.jp>,
James Morris <jmorris@...ei.org>,
linux-security-module@...r.kernel.org,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] file caps: update selinux xattr hooks
On Thu, 2007-06-28 at 13:22 -0500, Serge E. Hallyn wrote:
> This fixes a shortcoming of the cap_setfcap patch I sent earlier,
> pointed out by Stephen Smalley.
>
> Seems to compile and boot on my little systems.
>
> thanks,
> -serge
>
> >From d729000b922a2877a48ce2b5a03a9366d8c65d04 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@...ibm.com>
> Date: Thu, 28 Jun 2007 11:57:19 -0400
> Subject: [PATCH 1/1] file caps: update selinux xattr hooks
>
> SELinux does not call out to it's secondary module for setxattr
> or removexattr mediation, as the secondary module would
> incorrectly prevent writing of selinux xattrs. This means
> that when selinux and capability are both loaded, admins will
> be able to write file capabilities with CAP_SYS_ADMIN as before,
> not with CAP_SETFCAP.
>
> Update the selinux hooks to hardcode logic for the special
> consideration for file caps.
>
> I changed the flow of the removexattr hook to reduce the amount
> of indentation I was getting. It was probably written the way
> it was for a reason, and if it was, I apologize and will
> rewrite :) If it wasn't, hopefully this way is ok.
>
> Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
> ---
> security/selinux/hooks.c | 75 +++++++++++++++++++++++++++++----------------
> 1 files changed, 48 insertions(+), 27 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index af42820..db0a4ed 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2289,6 +2289,30 @@ static int selinux_inode_getattr(struct vfsmount *mnt, struct dentry *dentry)
> return dentry_has_perm(current, mnt, dentry, FILE__GETATTR);
> }
>
> +/* called by selinux_inode_setxattr to mediate setting
> + * of non-selinux xattrs */
> +static int selinux_inode_setotherxattr(struct dentry *dentry, char *name)
> +{
> + if (strncmp(name, XATTR_SECURITY_PREFIX,
> + sizeof XATTR_SECURITY_PREFIX - 1))
> + return dentry_has_perm(current, NULL, dentry, FILE__SETATTR);
> +
> + /* a file capability requires cap_setfcap */
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + else
> + return 0;
> + }
> +
> + /* A different attribute in the security namespace.
> + Restrict to administrator. */
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + return 0;
> +}
In reworking the flow of this code, you've changed the behavior (more so
than you intended) - your checking above only applies the FILE__SETATTR
check if dealing with a non-security attribute, whereas the original
logic (below) applied that check to all non-selinux attributes. So with
your new logic, we don't get any process-to-object check for
security.cap or security.<other>, and thus lose the domain-to-type check
or the level-to-level check.
> @@ -2299,19 +2323,8 @@ static int selinux_inode_setxattr(struct dentry *dentry, char *name, void *value
> u32 newsid;
> int rc = 0;
>
> - if (strcmp(name, XATTR_NAME_SELINUX)) {
> - if (!strncmp(name, XATTR_SECURITY_PREFIX,
> - sizeof XATTR_SECURITY_PREFIX - 1) &&
> - !capable(CAP_SYS_ADMIN)) {
> - /* A different attribute in the security namespace.
> - Restrict to administrator. */
> - return -EPERM;
> - }
Note that if setting a security.<non-selinux> attribute, we first check
the capability but then fall through on success to the FILE__SETATTR
check below.
> -
> - /* Not an attribute we recognize, so just check the
> - ordinary setattr permission. */
> - return dentry_has_perm(current, NULL, dentry, FILE__SETATTR);
> - }
> + if (strcmp(name, XATTR_NAME_SELINUX))
> + return selinux_inode_setotherxattr(dentry, name);
>
> sbsec = inode->i_sb->s_security;
> if (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)
> @@ -2385,24 +2398,32 @@ static int selinux_inode_listxattr (struct dentry *dentry)
>
> static int selinux_inode_removexattr (struct dentry *dentry, char *name)
> {
> - if (strcmp(name, XATTR_NAME_SELINUX)) {
> - if (!strncmp(name, XATTR_SECURITY_PREFIX,
> - sizeof XATTR_SECURITY_PREFIX - 1) &&
> - !capable(CAP_SYS_ADMIN)) {
> - /* A different attribute in the security namespace.
> - Restrict to administrator. */
> - return -EPERM;
> - }
> + /* No one is allowed to remove a SELinux security label.
> + You can change the label, but all data must be labeled. */
> + if (!strcmp(name, XATTR_NAME_SELINUX))
> + return -EACCES;
>
> - /* Not an attribute we recognize, so just check the
> - ordinary setattr permission. Might want a separate
> - permission for removexattr. */
> + /* Not an attribute we recognize, so just check the
> + ordinary setattr permission. Might want a separate
> + permission for removexattr. */
> + if (strncmp(name, XATTR_SECURITY_PREFIX,
> + sizeof XATTR_SECURITY_PREFIX - 1))
> return dentry_has_perm(current, NULL, dentry, FILE__SETATTR);
Same problem here - when you changed the flow, you unintentionally
changed the behavior.
> +
> + /* a file capability requires cap_setfcap */
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + else
> + return 0;
> }
>
> - /* No one is allowed to remove a SELinux security label.
> - You can change the label, but all data must be labeled. */
> - return -EACCES;
> + /* A different attribute in the security namespace.
> + Restrict to administrator. */
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + return 0;
> }
>
> static const char *selinux_inode_xattr_getsuffix(void)
--
Stephen Smalley
National Security Agency
-
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