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Date: Mon, 5 Oct 2015 11:08:46 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Andreas Gruenbacher <agruenba@...hat.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>
Cc: Paul Moore <paul@...l-moore.com>,
Eric Paris <eparis@...isplace.org>, selinux@...ho.nsa.gov
Subject: Re: [PATCH v2 1/2] security: Add hook to invalidate inode security
labels
On 10/04/2015 03:19 PM, Andreas Gruenbacher wrote:
> Add a hook to invalidate an inode's security label when the cached
> information becomes invalid.
>
> Implement the new hook in selinux: set a flag when a security label becomes
> invalid. When hitting a security label which has been marked as invalid in
> inode_has_perm, try reloading the label.
>
> If an inode does not have any dentries attached, we cannot reload its
> security label because we cannot use the getxattr inode operation. In that
> case, continue using the old, invalid label until a dentry becomes
> available.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> Cc: Paul Moore <paul@...l-moore.com>
> Cc: Stephen Smalley <sds@...ho.nsa.gov>
> Cc: Eric Paris <eparis@...isplace.org>
> Cc: selinux@...ho.nsa.gov
> ---
> include/linux/lsm_hooks.h | 6 ++++++
> include/linux/security.h | 5 +++++
> security/security.c | 8 ++++++++
> security/selinux/hooks.c | 23 +++++++++++++++++++++--
> security/selinux/include/objsec.h | 3 ++-
> 5 files changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index ec3a6ba..945ae1d 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1261,6 +1261,10 @@
> * audit_rule_init.
> * @rule contains the allocated rule
> *
> + * @inode_invalidate_secctx:
> + * Notify the security module that it must revalidate the security context
> + * of an inode.
> + *
> * @inode_notifysecctx:
> * Notify the security module of what the security context of an inode
> * should be. Initializes the incore security context managed by the
> @@ -1516,6 +1520,7 @@ union security_list_options {
> int (*secctx_to_secid)(const char *secdata, u32 seclen, u32 *secid);
> void (*release_secctx)(char *secdata, u32 seclen);
>
> + void (*inode_invalidate_secctx)(struct inode *inode);
> int (*inode_notifysecctx)(struct inode *inode, void *ctx, u32 ctxlen);
> int (*inode_setsecctx)(struct dentry *dentry, void *ctx, u32 ctxlen);
> int (*inode_getsecctx)(struct inode *inode, void **ctx, u32 *ctxlen);
> @@ -1757,6 +1762,7 @@ struct security_hook_heads {
> struct list_head secid_to_secctx;
> struct list_head secctx_to_secid;
> struct list_head release_secctx;
> + struct list_head inode_invalidate_secctx;
> struct list_head inode_notifysecctx;
> struct list_head inode_setsecctx;
> struct list_head inode_getsecctx;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 2f4c1f7..9692571 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -353,6 +353,7 @@ int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen);
> int security_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid);
> void security_release_secctx(char *secdata, u32 seclen);
>
> +void security_inode_invalidate_secctx(struct inode *inode);
> int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
> int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
> int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
> @@ -1093,6 +1094,10 @@ static inline void security_release_secctx(char *secdata, u32 seclen)
> {
> }
>
> +static inline void security_inode_invalidate_secctx(struct inode *inode)
> +{
> +}
> +
> static inline int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen)
> {
> return -EOPNOTSUPP;
> diff --git a/security/security.c b/security/security.c
> index 46f405c..e4371cd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1161,6 +1161,12 @@ void security_release_secctx(char *secdata, u32 seclen)
> }
> EXPORT_SYMBOL(security_release_secctx);
>
> +void security_inode_invalidate_secctx(struct inode *inode)
> +{
> + call_void_hook(inode_invalidate_secctx, inode);
> +}
> +EXPORT_SYMBOL(security_inode_invalidate_secctx);
> +
> int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen)
> {
> return call_int_hook(inode_notifysecctx, 0, inode, ctx, ctxlen);
> @@ -1763,6 +1769,8 @@ struct security_hook_heads security_hook_heads = {
> LIST_HEAD_INIT(security_hook_heads.secctx_to_secid),
> .release_secctx =
> LIST_HEAD_INIT(security_hook_heads.release_secctx),
> + .inode_invalidate_secctx =
> + LIST_HEAD_INIT(security_hook_heads.inode_invalidate_secctx),
> .inode_notifysecctx =
> LIST_HEAD_INIT(security_hook_heads.inode_notifysecctx),
> .inode_setsecctx =
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index e4369d8..c5e4ca8 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1293,11 +1293,11 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
> unsigned len = 0;
> int rc = 0;
>
> - if (isec->initialized)
> + if (isec->initialized == 1)
> goto out;
>
> mutex_lock(&isec->lock);
> - if (isec->initialized)
> + if (isec->initialized == 1)
> goto out_unlock;
>
> sbsec = inode->i_sb->s_security;
> @@ -1625,6 +1625,14 @@ static int inode_has_perm(const struct cred *cred,
> sid = cred_sid(cred);
> isec = inode->i_security;
>
> + /*
> + * Try reloading the inode security label when it has been invalidated.
> + * This will fail if no dentry for this inode can be found; in that case,
> + * we will continue using the old label.
> + */
> + if (isec->initialized == 2)
> + inode_doinit(inode);
Not fond of these magic initialized values.
Is it always safe to call inode_doinit() from all callers of
inode_has_perm()?
What about the cases where isec->sid is used without going through
inode_has_perm()?
> +
> return avc_has_perm(sid, isec->sid, isec->sclass, perms, adp);
> }
>
> @@ -3509,6 +3517,7 @@ static int selinux_file_open(struct file *file, const struct cred *cred)
>
> fsec = file->f_security;
> isec = file_inode(file)->i_security;
> +
> /*
> * Save inode label and policy sequence number
> * at open-time so that selinux_file_permission
> @@ -5762,6 +5771,15 @@ static void selinux_release_secctx(char *secdata, u32 seclen)
> kfree(secdata);
> }
>
> +static void selinux_inode_invalidate_secctx(struct inode *inode)
> +{
> + struct inode_security_struct *isec = inode->i_security;
> +
> + mutex_lock(&isec->lock);
> + isec->initialized = 2;
> + mutex_unlock(&isec->lock);
> +}
> +
> /*
> * called with inode->i_mutex locked
> */
> @@ -5993,6 +6011,7 @@ static struct security_hook_list selinux_hooks[] = {
> LSM_HOOK_INIT(secid_to_secctx, selinux_secid_to_secctx),
> LSM_HOOK_INIT(secctx_to_secid, selinux_secctx_to_secid),
> LSM_HOOK_INIT(release_secctx, selinux_release_secctx),
> + LSM_HOOK_INIT(inode_invalidate_secctx, selinux_inode_invalidate_secctx),
> LSM_HOOK_INIT(inode_notifysecctx, selinux_inode_notifysecctx),
> LSM_HOOK_INIT(inode_setsecctx, selinux_inode_setsecctx),
> LSM_HOOK_INIT(inode_getsecctx, selinux_inode_getsecctx),
> diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
> index 81fa718..6d1fe19 100644
> --- a/security/selinux/include/objsec.h
> +++ b/security/selinux/include/objsec.h
> @@ -46,7 +46,8 @@ struct inode_security_struct {
> u32 task_sid; /* SID of creating task */
> u32 sid; /* SID of this object */
> u16 sclass; /* security class of this object */
> - unsigned char initialized; /* initialization flag */
> + unsigned char initialized; /* 0: not initialized, 1: initialized,
> + 2: invalidated */
> struct mutex lock;
> };
>
>
--
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