linux-kernel - [PATCH] tmpfs: security xattr setting on inode creation

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Message-Id: <1329990365-23779-1-git-send-email-jarkko.sakkinen@intel.com>
Date:	Thu, 23 Feb 2012 11:46:05 +0200
From:	Jarkko Sakkinen <jarkko.sakkinen@...el.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>
Subject: [PATCH] tmpfs: security xattr setting on inode creation

Adds to generic xattr support introduced in Linux 3.0 by
implementing initxattrs callback. This enables consulting
of security attributes from LSM and EVM when inode is
created.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...el.com>
---
 mm/shmem.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 files changed, 66 insertions(+), 16 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 7a45ad0..cd367b1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1478,6 +1478,64 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
 }
 
 /*
+ * Allocate new xattr.
+ */
+static int shmem_xattr_alloc(size_t size, struct shmem_xattr **new_xattr)
+{
+	/* wrap around? */
+	size_t len = sizeof(**new_xattr) + size;
+	if (len <= sizeof(**new_xattr))
+		return -ENOMEM;
+
+	*new_xattr = kmalloc(len, GFP_KERNEL);
+	if (*new_xattr == NULL)
+		return -ENOMEM;
+
+	(*new_xattr)->size = size;
+	return 0;
+}
+
+/*
+ * Callback for security_inode_init_security() for acquiring xattrs.
+ */
+static int shmem_initxattrs(struct inode *inode,
+			    const struct xattr *xattr_array,
+			    void *fs_info)
+{
+	const struct xattr *xattr;
+	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_xattr *new_xattr = NULL;
+	size_t len;
+	int err = 0;
+
+	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
+		err = shmem_xattr_alloc(xattr->value_len, &new_xattr);
+		if (err < 0)
+			return err;
+
+		len = strlen(xattr->name) + 1;
+		new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
+					  GFP_KERNEL);
+		if (new_xattr->name == NULL) {
+			kfree(new_xattr);
+			return -ENOMEM;
+		}
+
+		memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
+		       XATTR_SECURITY_PREFIX_LEN);
+		memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
+		       xattr->name, len);
+		memcpy(new_xattr->value, xattr->value, xattr->value_len);
+
+		spin_lock(&info->lock);
+		list_add(&new_xattr->list, &info->xattr_list);
+		spin_unlock(&info->lock);
+	}
+
+	return 0;
+}
+
+/*
  * File creation. Allocate an inode, and we're done..
  */
 static int
@@ -1490,7 +1548,7 @@ shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
 	if (inode) {
 		error = security_inode_init_security(inode, dir,
 						     &dentry->d_name,
-						     NULL, NULL);
+						     &shmem_initxattrs, NULL);
 		if (error) {
 			if (error != -EOPNOTSUPP) {
 				iput(inode);
@@ -1630,7 +1688,7 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
 		return -ENOSPC;
 
 	error = security_inode_init_security(inode, dir, &dentry->d_name,
-					     NULL, NULL);
+					     &shmem_initxattrs, NULL);
 	if (error) {
 		if (error != -EOPNOTSUPP) {
 			iput(inode);
@@ -1731,26 +1789,19 @@ static int shmem_xattr_get(struct dentry *dentry, const char *name,
 	return ret;
 }
 
-static int shmem_xattr_set(struct dentry *dentry, const char *name,
+static int shmem_xattr_set(struct inode *inode, const char *name,
 			   const void *value, size_t size, int flags)
 {
-	struct inode *inode = dentry->d_inode;
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_xattr *xattr;
 	struct shmem_xattr *new_xattr = NULL;
-	size_t len;
 	int err = 0;
 
 	/* value == NULL means remove */
 	if (value) {
-		/* wrap around? */
-		len = sizeof(*new_xattr) + size;
-		if (len <= sizeof(*new_xattr))
-			return -ENOMEM;
-
-		new_xattr = kmalloc(len, GFP_KERNEL);
-		if (!new_xattr)
-			return -ENOMEM;
+		err = shmem_xattr_alloc(size, &new_xattr);
+		if (err < 0)
+			return err;
 
 		new_xattr->name = kstrdup(name, GFP_KERNEL);
 		if (!new_xattr->name) {
@@ -1758,7 +1809,6 @@ static int shmem_xattr_set(struct dentry *dentry, const char *name,
 			return -ENOMEM;
 		}
 
-		new_xattr->size = size;
 		memcpy(new_xattr->value, value, size);
 	}
 
@@ -1858,7 +1908,7 @@ static int shmem_setxattr(struct dentry *dentry, const char *name,
 	if (size == 0)
 		value = "";  /* empty EA, do not remove */
 
-	return shmem_xattr_set(dentry, name, value, size, flags);
+	return shmem_xattr_set(dentry->d_inode, name, value, size, flags);
 
 }
 
@@ -1878,7 +1928,7 @@ static int shmem_removexattr(struct dentry *dentry, const char *name)
 	if (err)
 		return err;
 
-	return shmem_xattr_set(dentry, name, NULL, 0, XATTR_REPLACE);
+	return shmem_xattr_set(dentry->d_inode, name, NULL, 0, XATTR_REPLACE);
 }
 
 static bool xattr_is_trusted(const char *name)
-- 
1.7.5.4

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