[PATCH v4 25/30] evm: remove evm_xattr_acl_change()

[Christian Brauner]

The security and integrity infrastructure has dedicated hooks now so
evm_xattr_acl_change() is dead code. Before this commit the callchain was:

evm_protect_xattr()
-> evm_xattr_change()
   -> evm_xattr_acl_change()

where evm_protect_xattr() was hit from evm_inode_setxattr() and
evm_inode_removexattr(). But now we have evm_inode_set_acl() and
evm_inode_remove_acl() and have switched over the vfs to rely on the posix
acl api so the code isn't hit anymore.

Suggested-by: Paul Moore <paul at paul-moore.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner at kernel.org>
---

Notes:
    /* v2 */
    unchanged
    
    /* v3 */
    Paul Moore <paul at paul-moore.com>:
    - Remove evm_xattr_acl_change() completely.
    
    /* v4 */
    unchanged

 security/integrity/evm/evm_main.c | 64 -------------------------------
 1 file changed, 64 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 7904786b610f..e0d120383870 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -434,66 +434,6 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
 	return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
 }
 
-/*
- * evm_xattr_acl_change - check if passed ACL changes the inode mode
- * @mnt_userns: user namespace of the idmapped mount
- * @dentry: pointer to the affected dentry
- * @xattr_name: requested xattr
- * @xattr_value: requested xattr value
- * @xattr_value_len: requested xattr value length
- *
- * Check if passed ACL changes the inode mode, which is protected by EVM.
- *
- * Returns 1 if passed ACL causes inode mode change, 0 otherwise.
- */
-static int evm_xattr_acl_change(struct user_namespace *mnt_userns,
-				struct dentry *dentry, const char *xattr_name,
-				const void *xattr_value, size_t xattr_value_len)
-{
-#ifdef CONFIG_FS_POSIX_ACL
-	umode_t mode;
-	struct posix_acl *acl = NULL, *acl_res;
-	struct inode *inode = d_backing_inode(dentry);
-	int rc;
-
-	/*
-	 * An earlier comment here mentioned that the idmappings for
-	 * ACL_{GROUP,USER} don't matter since EVM is only interested in the
-	 * mode stored as part of POSIX ACLs. Nonetheless, if it must translate
-	 * from the uapi POSIX ACL representation to the VFS internal POSIX ACL
-	 * representation it should do so correctly. There's no guarantee that
-	 * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters
-	 * for the mode at some point and it's difficult to keep track of all
-	 * the LSM and integrity modules and what they do to POSIX ACLs.
-	 *
-	 * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX
-	 * ACLs it received. It requires knowledge that only the VFS is
-	 * guaranteed to have.
-	 */
-	acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode),
-				  xattr_value, xattr_value_len);
-	if (IS_ERR_OR_NULL(acl))
-		return 1;
-
-	acl_res = acl;
-	/*
-	 * Passing mnt_userns is necessary to correctly determine the GID in
-	 * an idmapped mount, as the GID is used to clear the setgid bit in
-	 * the inode mode.
-	 */
-	rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res);
-
-	posix_acl_release(acl);
-
-	if (rc)
-		return 1;
-
-	if (inode->i_mode != mode)
-		return 1;
-#endif
-	return 0;
-}
-
 /*
  * evm_xattr_change - check if passed xattr value differs from current value
  * @mnt_userns: user namespace of the idmapped mount
@@ -513,10 +453,6 @@ static int evm_xattr_change(struct user_namespace *mnt_userns,
 	char *xattr_data = NULL;
 	int rc = 0;
 
-	if (posix_xattr_acl(xattr_name))
-		return evm_xattr_acl_change(mnt_userns, dentry, xattr_name,
-					    xattr_value, xattr_value_len);
-
 	rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data,
 				0, GFP_NOFS);
 	if (rc < 0)
-- 
2.34.1