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SubjectRe: [PATCH 1/1] file caps: update selinux xattr hooks
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On Mon, 2007-07-02 at 17:06 -0500, Serge E. Hallyn wrote:
> Thanks Stephen, does the following version appear correct? It just
> checks for a different cap for security.capability, then if granted
> goes on to check FILE__GETATTR before granting setxattr or removexattr
> on any security.* xattr.
>
> thanks,
> -serge
>
> >From 5ec50bc22d3320565002658433829f7dc5bc0aa5 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@us.ibm.com>
> Date: Mon, 2 Jul 2007 14:07:51 -0400
> Subject: [PATCH 1/1] file caps: update selinux xattr hooks (v2)
>
> 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.
>
> Note that the setxattr and removexattr logic for non selinux
> attrs appears to be identical. So I do have another patch
> where selinux_inode_setotherxattr takes an extra argument
> u32 av (in case removexattr ever gets its own av permission)
> so removexattr can shrink and just use that. But first I
> thought I'd see if this version is even close correct :)

Yes, looks sane, and feel free to have both hooks use a common helper
for non-selinux attributes. I don't think you even need to bother with
the u32 av argument; if we later split the check, we can change it then
(it isn't as though these functions need to have a stable interface).

>
> Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
> ---
> security/selinux/hooks.c | 48 ++++++++++++++++++++++++++++-----------------
> 1 files changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index af42820..336525c 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2289,6 +2289,25 @@ static int selinux_inode_getattr(struct vfsmount *mnt, struct dentry *dentry)
> return dentry_has_perm(current, mnt, dentry, FILE__GETATTR);
> }
>
> +static int selinux_inode_setotherxattr(struct dentry *dentry, char *name)
> +{
> + if (!strncmp(name, XATTR_SECURITY_PREFIX,
> + sizeof XATTR_SECURITY_PREFIX - 1)) {
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + } else if (!capable(CAP_SYS_ADMIN)) {
> + /* A different attribute in the security namespace.
> + Restrict to administrator. */
> + return -EPERM;
> + }
> + }
> +
> + /* Not an attribute we recognize, so just check the
> + ordinary setattr permission. */
> + return dentry_has_perm(current, NULL, dentry, FILE__SETATTR);
> +}
> +
> static int selinux_inode_setxattr(struct dentry *dentry, char *name, void *value, size_t size, int flags)
> {
> struct task_security_struct *tsec = current->security;
> @@ -2299,19 +2318,8 @@ 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;
> - }
> -
> - /* 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)
> @@ -2387,11 +2395,15 @@ 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;
> + sizeof XATTR_SECURITY_PREFIX - 1)) {
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + } else if (!capable(CAP_SYS_ADMIN)) {
> + /* A different attribute in the security
> + namespace. Restrict to administrator. */
> + return -EPERM;
> + }
> }
>
> /* Not an attribute we recognize, so just check the
--
Stephen Smalley
National Security Agency

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