[PATCH] Do not require attributes for security_inode_init_security.

[Greg Wettstein]

The integration of the Integrity Measurement Architecture (IMA)
into the LSM infrastructure introduced a conditional check that
denies access to the security_inode_init_security() event handler
if the LSM extended attribute 'blob' size is 0.

This changes the previous behavior of this event handler and
results in variable behavior of LSM's depending on the LSM boot
configuration.

Modify the function so that it removes the need for a non-zero
extended attribute blob size and bypasses the memory allocation
and freeing that is not needed if the LSM infrastructure is not
using extended attributes.

Use a break statement to exit the loop that is iterating over the
defined handlers for this event if a halting error condition is
generated by one of the invoked LSM handlers.  The checks for how
to handle cleanup are executed at the end of the loop regardless
of how the loop terminates.

A two exit label strategy is implemented.  One of the exit
labels is a target for the no attribute case while the second is
the target for the case where memory allocated for processing of
extended attributes needs to be freed.

Signed-off-by: Greg Wettstein <greg at enjellic.com>
---
 security/security.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/security/security.c b/security/security.c
index 7035ee35a393..a0b52b964688 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1717,10 +1717,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
-	if (!blob_sizes.lbs_xattr_count)
-		return 0;
-
-	if (initxattrs) {
+	if (blob_sizes.lbs_xattr_count && initxattrs) {
 		/* Allocate +1 for EVM and +1 as terminator. */
 		new_xattrs = kcalloc(blob_sizes.lbs_xattr_count + 2,
 				     sizeof(*new_xattrs), GFP_NOFS);
@@ -1733,7 +1730,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 		ret = hp->hook.inode_init_security(inode, dir, qstr, new_xattrs,
 						  &xattr_count);
 		if (ret && ret != -EOPNOTSUPP)
-			goto out;
+			break;
 		/*
 		 * As documented in lsm_hooks.h, -EOPNOTSUPP in this context
 		 * means that the LSM is not willing to provide an xattr, not
@@ -1742,19 +1739,22 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 		 */
 	}
 
-	/* If initxattrs() is NULL, xattr_count is zero, skip the call. */
-	if (!xattr_count)
-		goto out;
+	/* Skip xattr processing if no attributes are in use. */
+	if (!blob_sizes.lbs_xattr_count)
+		goto out2;
+	/* No attrs or an LSM returned an actionable error code. */
+	if (!xattr_count || (ret && ret != -EOPNOTSUPP))
+		goto out1;
 
 	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs,
 				      &xattr_count);
-	if (ret)
-		goto out;
-	ret = initxattrs(inode, new_xattrs, fs_data);
-out:
+	if (!ret)
+		ret = initxattrs(inode, new_xattrs, fs_data);
+ out1:
 	for (; xattr_count > 0; xattr_count--)
 		kfree(new_xattrs[xattr_count - 1].value);
 	kfree(new_xattrs);
+ out2:
 	return (ret == -EOPNOTSUPP) ? 0 : ret;
 }
 EXPORT_SYMBOL(security_inode_init_security);
-- 
2.39.1