Re: [PATCH v12 10/11] SELinux: Add selfattr hooks

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On 29/06/2023 21:55, 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@xxxxxxxxxxxxxxxx>
Cc: selinux@xxxxxxxxxxxxxxx
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
---
  security/selinux/hooks.c | 148 ++++++++++++++++++++++++++++++++-------
  1 file changed, 121 insertions(+), 27 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 49ec74bc006c..a4a536552717 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6226,8 +6226,8 @@ 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;
@@ -6244,20 +6244,27 @@ 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();
@@ -6275,7 +6282,7 @@ 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;
@@ -6286,23 +6293,31 @@ 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;
@@ -6314,13 +6329,14 @@ 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
@@ -6331,7 +6347,8 @@ 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;
@@ -6354,11 +6371,11 @@ 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);
@@ -6366,9 +6383,9 @@ 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;
@@ -6410,6 +6427,81 @@ 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;
+
+	*size = total_len;
+	if (rc < 0)
+		return rc;
+	return 1;
+}
+
+static int selinux_setselfattr(unsigned int __user attr,
+			       struct lsm_ctx __user *ctx, size_t __user size,
+			       u32 __user flags)
+{
+	struct lsm_ctx *lctx;
+	int rc;
+
+	lctx = kmalloc(size, GFP_KERNEL);
+	if (lctx == NULL)
+		return -ENOMEM;
+
+	if (copy_from_user(lctx, ctx, size))
+		rc = -EFAULT;
+	else if (lctx->ctx_len > size)

Isn't this check redundant with the ones from security_setselfattr()?

This also applies to AppArmor and Smack patches. It would be simpler to move the common code/checks to security_setselfattr().


+		rc = -EINVAL;

The Smack implementation returns E2BIG instead. It would be a good idea to return the same kind of error code, and document it. Again, factoring out the common part would help.


+	else
+		rc = selinux_lsm_setattr(attr, lctx->ctx, lctx->ctx_len);
+
+	kfree(lctx);
+	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);
@@ -7041,6 +7133,8 @@ 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),



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