VFS/Security: Rework inode_getsecurity and callers to return resulting buffer

This patch modifies the interface to inode_getsecurity to have the function
return a buffer containing the security blob and its length via parameters
instead of relying on the calling function to give it an appropriately sized
buffer.

Security blobs obtained with this function should be freed using the
release_secctx LSM hook.  This alleviates the problem of the caller having to
guess a length and preallocate a buffer for this function allowing it to be
used elsewhere for Labeled NFS.

The patch also removed the unused err parameter.  The conversion is similar to
the one performed by Al Viro for the security_getprocattr hook.

Signed-off-by: David P. Quigley <dpquigl@tycho.nsa.gov>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Chris Wright <chrisw@sous-sol.org>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 2 deletions

diff --git a/fs/xattr.c b/fs/xattr.c
index 6645b7313b33..1858552a6a1a 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -105,6 +105,33 @@ out:
 EXPORT_SYMBOL_GPL(vfs_setxattr);
 
 ssize_t
+xattr_getsecurity(struct inode *inode, const char *name, void *value,
+			size_t size)
+{
+	void *buffer = NULL;
+	ssize_t len;
+
+	if (!value || !size) {
+		len = security_inode_getsecurity(inode, name, &buffer, false);
+		goto out_noalloc;
+	}
+
+	len = security_inode_getsecurity(inode, name, &buffer, true);
+	if (len < 0)
+		return len;
+	if (size < len) {
+		len = -ERANGE;
+		goto out;
+	}
+	memcpy(value, buffer, len);
+out:
+	security_release_secctx(buffer, len);
+out_noalloc:
+	return len;
+}
+EXPORT_SYMBOL_GPL(xattr_getsecurity);
+
+ssize_t
 vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
 {
 	struct inode *inode = dentry->d_inode;
@@ -126,8 +153,7 @@ vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
 	if (!strncmp(name, XATTR_SECURITY_PREFIX,
 				XATTR_SECURITY_PREFIX_LEN)) {
 		const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
-		int ret = security_inode_getsecurity(inode, suffix, value,
-						     size, error);
+		int ret = xattr_getsecurity(inode, suffix, value, size);
 		/*
 		 * Only overwrite the return value if a security module
 		 * is actually active.