[PATCH v13 10/11] SELinux: Add selfattr hooks

[PATCH v13 10/11] SELinux: Add selfattr hooks

[Casey Schaufler]

Add hooks for setselfattr and getselfattr. These hooks are not very
different from their setprocattr and getprocattr equivalents, and
much of the code is shared.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Cc: selinux@vger.kernel.org
Cc: Paul Moore <paul@paul-moore.com>
---
 security/selinux/hooks.c | 136 +++++++++++++++++++++++++++++++--------
 1 file changed, 109 insertions(+), 27 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c900813fc8f7..f66a28f672b2 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6265,8 +6265,8 @@ static void selinux_d_instantiate(struct dentry *dentry, struct inode *inode)
 		inode_doinit_with_dentry(inode, dentry);
 }
 
-static int selinux_getprocattr(struct task_struct *p,
-			       const char *name, char **value)
+static int selinux_lsm_getattr(unsigned int attr, struct task_struct *p,
+			       char **value)
 {
 	const struct task_security_struct *__tsec;
 	u32 sid;
@@ -6283,20 +6283,27 @@ static int selinux_getprocattr(struct task_struct *p,
 			goto bad;
 	}
 
-	if (!strcmp(name, "current"))
+	switch (attr) {
+	case LSM_ATTR_CURRENT:
 		sid = __tsec->sid;
-	else if (!strcmp(name, "prev"))
+		break;
+	case LSM_ATTR_PREV:
 		sid = __tsec->osid;
-	else if (!strcmp(name, "exec"))
+		break;
+	case LSM_ATTR_EXEC:
 		sid = __tsec->exec_sid;
-	else if (!strcmp(name, "fscreate"))
+		break;
+	case LSM_ATTR_FSCREATE:
 		sid = __tsec->create_sid;
-	else if (!strcmp(name, "keycreate"))
+		break;
+	case LSM_ATTR_KEYCREATE:
 		sid = __tsec->keycreate_sid;
-	else if (!strcmp(name, "sockcreate"))
+		break;
+	case LSM_ATTR_SOCKCREATE:
 		sid = __tsec->sockcreate_sid;
-	else {
-		error = -EINVAL;
+		break;
+	default:
+		error = -EOPNOTSUPP;
 		goto bad;
 	}
 	rcu_read_unlock();
@@ -6314,7 +6321,7 @@ static int selinux_getprocattr(struct task_struct *p,
 	return error;
 }
 
-static int selinux_setprocattr(const char *name, void *value, size_t size)
+static int selinux_lsm_setattr(u64 attr, void *value, size_t size)
 {
 	struct task_security_struct *tsec;
 	struct cred *new;
@@ -6325,23 +6332,31 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 	/*
 	 * Basic control over ability to set these attributes at all.
 	 */
-	if (!strcmp(name, "exec"))
+	switch (attr) {
+	case LSM_ATTR_EXEC:
 		error = avc_has_perm(mysid, mysid, SECCLASS_PROCESS,
 				     PROCESS__SETEXEC, NULL);
-	else if (!strcmp(name, "fscreate"))
+		break;
+	case LSM_ATTR_FSCREATE:
 		error = avc_has_perm(mysid, mysid, SECCLASS_PROCESS,
 				     PROCESS__SETFSCREATE, NULL);
-	else if (!strcmp(name, "keycreate"))
+		break;
+	case LSM_ATTR_KEYCREATE:
 		error = avc_has_perm(mysid, mysid, SECCLASS_PROCESS,
 				     PROCESS__SETKEYCREATE, NULL);
-	else if (!strcmp(name, "sockcreate"))
+		break;
+	case LSM_ATTR_SOCKCREATE:
 		error = avc_has_perm(mysid, mysid, SECCLASS_PROCESS,
 				     PROCESS__SETSOCKCREATE, NULL);
-	else if (!strcmp(name, "current"))
+		break;
+	case LSM_ATTR_CURRENT:
 		error = avc_has_perm(mysid, mysid, SECCLASS_PROCESS,
 				     PROCESS__SETCURRENT, NULL);
-	else
-		error = -EINVAL;
+		break;
+	default:
+		error = -EOPNOTSUPP;
+		break;
+	}
 	if (error)
 		return error;
 
@@ -6353,13 +6368,14 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 		}
 		error = security_context_to_sid(value, size,
 						&sid, GFP_KERNEL);
-		if (error == -EINVAL && !strcmp(name, "fscreate")) {
+		if (error == -EINVAL && attr == LSM_ATTR_FSCREATE) {
 			if (!has_cap_mac_admin(true)) {
 				struct audit_buffer *ab;
 				size_t audit_size;
 
-				/* We strip a nul only if it is at the end, otherwise the
-				 * context contains a nul and we should audit that */
+				/* We strip a nul only if it is at the end,
+				 * otherwise the context contains a nul and
+				 * we should audit that */
 				if (str[size - 1] == '\0')
 					audit_size = size - 1;
 				else
@@ -6370,7 +6386,8 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 				if (!ab)
 					return error;
 				audit_log_format(ab, "op=fscreate invalid_context=");
-				audit_log_n_untrustedstring(ab, value, audit_size);
+				audit_log_n_untrustedstring(ab, value,
+							    audit_size);
 				audit_log_end(ab);
 
 				return error;
@@ -6393,11 +6410,11 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 	   checks and may_create for the file creation checks. The
 	   operation will then fail if the context is not permitted. */
 	tsec = selinux_cred(new);
-	if (!strcmp(name, "exec")) {
+	if (attr == LSM_ATTR_EXEC) {
 		tsec->exec_sid = sid;
-	} else if (!strcmp(name, "fscreate")) {
+	} else if (attr == LSM_ATTR_FSCREATE) {
 		tsec->create_sid = sid;
-	} else if (!strcmp(name, "keycreate")) {
+	} else if (attr == LSM_ATTR_KEYCREATE) {
 		if (sid) {
 			error = avc_has_perm(mysid, sid,
 					     SECCLASS_KEY, KEY__CREATE, NULL);
@@ -6405,9 +6422,9 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 				goto abort_change;
 		}
 		tsec->keycreate_sid = sid;
-	} else if (!strcmp(name, "sockcreate")) {
+	} else if (attr == LSM_ATTR_SOCKCREATE) {
 		tsec->sockcreate_sid = sid;
-	} else if (!strcmp(name, "current")) {
+	} else if (attr == LSM_ATTR_CURRENT) {
 		error = -EINVAL;
 		if (sid == 0)
 			goto abort_change;
@@ -6449,6 +6466,69 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 	return error;
 }
 
+static int selinux_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
+			       size_t *size, u32 flags)
+{
+	char *value;
+	size_t total_len;
+	int len;
+	int rc;
+
+	len = selinux_lsm_getattr(attr, current, &value);
+	if (len < 0)
+		return len;
+
+	total_len = ALIGN(struct_size(ctx, ctx, len), 8);
+
+	if (total_len > *size)
+		rc = -E2BIG;
+	else if (ctx)
+		rc = lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
+	else
+		rc = 1;
+
+	kfree(value);
+	*size = total_len;
+	if (rc < 0)
+		return rc;
+	return 1;
+}
+
+static int selinux_setselfattr(unsigned int __user attr, struct lsm_ctx *ctx,
+			       size_t __user size, u32 __user flags)
+{
+	int rc;
+
+	rc = selinux_lsm_setattr(attr, ctx->ctx, ctx->ctx_len);
+	if (rc > 0)
+		return 0;
+	return rc;
+}
+
+static int selinux_getprocattr(struct task_struct *p,
+			       const char *name, char **value)
+{
+	unsigned int attr = lsm_name_to_attr(name);
+	int rc;
+
+	if (attr) {
+		rc = selinux_lsm_getattr(attr, p, value);
+		if (rc != -EOPNOTSUPP)
+			return rc;
+	}
+
+	return -EINVAL;
+}
+
+static int selinux_setprocattr(const char *name, void *value, size_t size)
+{
+	int attr = lsm_name_to_attr(name);
+
+	if (attr)
+		return selinux_lsm_setattr(attr, value, size);
+	return -EINVAL;
+}
+
 static int selinux_ismaclabel(const char *name)
 {
 	return (strcmp(name, XATTR_SELINUX_SUFFIX) == 0);
@@ -7080,6 +7160,8 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 
 	LSM_HOOK_INIT(d_instantiate, selinux_d_instantiate),
 
+	LSM_HOOK_INIT(getselfattr, selinux_getselfattr),
+	LSM_HOOK_INIT(setselfattr, selinux_setselfattr),
 	LSM_HOOK_INIT(getprocattr, selinux_getprocattr),
 	LSM_HOOK_INIT(setprocattr, selinux_setprocattr),
 
-- 
2.41.0

Re: [PATCH v13 10/11] SELinux: Add selfattr hooks

[Paul Moore]

On Aug  2, 2023 Casey Schaufler <casey@schaufler-ca.com> wrote:
> 
> Add hooks for setselfattr and getselfattr. These hooks are not very
> different from their setprocattr and getprocattr equivalents, and
> much of the code is shared.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Cc: selinux@vger.kernel.org
> Cc: Paul Moore <paul@paul-moore.com>
> ---
>  security/selinux/hooks.c | 136 +++++++++++++++++++++++++++++++--------
>  1 file changed, 109 insertions(+), 27 deletions(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index c900813fc8f7..f66a28f672b2 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c

...

> @@ -6449,6 +6466,69 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
>  	return error;
>  }
>  
> +static int selinux_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
> +			       size_t *size, u32 flags)
> +{
> +	char *value;
> +	size_t total_len;
> +	int len;
> +	int rc;
> +
> +	len = selinux_lsm_getattr(attr, current, &value);
> +	if (len < 0)
> +		return len;
> +
> +	total_len = ALIGN(struct_size(ctx, ctx, len), 8);
> +
> +	if (total_len > *size)
> +		rc = -E2BIG;
> +	else if (ctx)
> +		rc = lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
> +	else
> +		rc = 1;

I'd probably either set rc to zero when at declaration time and drop
this final else, or explicitly set rc to one here to better fit what
lsm_fill_user_ctx() does on success.  However, the end result is the
same so we can just fix that with a follow-up patch once this is
merged into the lsm/next branch.

> +	kfree(value);
> +	*size = total_len;
> +	if (rc < 0)
> +		return rc;
> +	return 1;
> +}

--
paul-moore.com

Re: [PATCH v13 10/11] SELinux: Add selfattr hooks

[Mickaël Salaün]

On Wed, Aug 02, 2023 at 10:44:33AM -0700, Casey Schaufler wrote:
> Add hooks for setselfattr and getselfattr. These hooks are not very
> different from their setprocattr and getprocattr equivalents, and
> much of the code is shared.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Cc: selinux@vger.kernel.org
> Cc: Paul Moore <paul@paul-moore.com>
> ---
>  security/selinux/hooks.c | 136 +++++++++++++++++++++++++++++++--------
>  1 file changed, 109 insertions(+), 27 deletions(-)

> +static int selinux_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
> +			       size_t *size, u32 flags)
> +{
> +	char *value;
> +	size_t total_len;
> +	int len;
> +	int rc;
> +
> +	len = selinux_lsm_getattr(attr, current, &value);
> +	if (len < 0)
> +		return len;
> +
> +	total_len = ALIGN(struct_size(ctx, ctx, len), 8);
> +
> +	if (total_len > *size)

It looks a bit weird that size must be greater than all the LSM
attributes even when ctx is NULL. Same for other getselfattr hook
implementations.

> +		rc = -E2BIG;
> +	else if (ctx)
> +		rc = lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
> +	else
> +		rc = 1;

Agreed with Paul, we should initialize rc to zero.

> +
> +	kfree(value);
> +	*size = total_len;
> +	if (rc < 0)
> +		return rc;
> +	return 1;
> +}
> +
> +static int selinux_setselfattr(unsigned int __user attr, struct lsm_ctx *ctx,
> +			       size_t __user size, u32 __user flags)

This __user attribute is dedicated to user pointers, not values.

> +{
> +	int rc;
> +

Good to see this refactoring!

> +	rc = selinux_lsm_setattr(attr, ctx->ctx, ctx->ctx_len);
> +	if (rc > 0)
> +		return 0;
> +	return rc;
> +}
> +
> +static int selinux_getprocattr(struct task_struct *p,
> +			       const char *name, char **value)
> +{
> +	unsigned int attr = lsm_name_to_attr(name);
> +	int rc;
> +
> +	if (attr) {
> +		rc = selinux_lsm_getattr(attr, p, value);
> +		if (rc != -EOPNOTSUPP)
> +			return rc;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int selinux_setprocattr(const char *name, void *value, size_t size)
> +{
> +	int attr = lsm_name_to_attr(name);
> +
> +	if (attr)
> +		return selinux_lsm_setattr(attr, value, size);
> +	return -EINVAL;
> +}
> +
>  static int selinux_ismaclabel(const char *name)
>  {
>  	return (strcmp(name, XATTR_SELINUX_SUFFIX) == 0);
> @@ -7080,6 +7160,8 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>  
>  	LSM_HOOK_INIT(d_instantiate, selinux_d_instantiate),
>  
> +	LSM_HOOK_INIT(getselfattr, selinux_getselfattr),
> +	LSM_HOOK_INIT(setselfattr, selinux_setselfattr),
>  	LSM_HOOK_INIT(getprocattr, selinux_getprocattr),
>  	LSM_HOOK_INIT(setprocattr, selinux_setprocattr),
>  
> -- 
> 2.41.0
>