The posix acl api provides a dedicated security and integrity hook for
setting posix acls. This means that
evm_protect_xattr()
-> evm_xattr_change()
-> evm_xattr_acl_change()
is now only hit during vfs_remove_acl() at which point we are guaranteed
that xattr_value and xattr_value_len are NULL and 0. In this case evm
always used to return 1. Simplify this function to do just that.
Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
---
security/integrity/evm/evm_main.c | 62 +++++++------------------------
1 file changed, 14 insertions(+), 48 deletions(-)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 15aa5995fff4..1fbe1b8d0364 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -436,62 +436,29 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
/*
* 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.
+ * This is only hit during xattr removal at which point we always return 1.
+ * Splat a warning in case someone managed to pass data to this function. That
+ * should never happen.
*
* 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)
+static int evm_xattr_acl_change(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;
+ int rc = 0;
- if (inode->i_mode != mode)
- return 1;
+#ifdef CONFIG_FS_POSIX_ACL
+ WARN_ONCE(xattr_value != NULL,
+ "Passing xattr value for POSIX ACLs not supported\n");
+ WARN_ONCE(xattr_value_len != 0,
+ "Passing non-zero length for POSIX ACLs not supported\n");
+ rc = 1;
#endif
- return 0;
+
+ return rc;
}
/*
@@ -514,8 +481,7 @@ static int evm_xattr_change(struct user_namespace *mnt_userns,
int rc = 0;
if (posix_xattr_acl(xattr_name))
- return evm_xattr_acl_change(mnt_userns, dentry, xattr_name,
- xattr_value, xattr_value_len);
+ return evm_xattr_acl_change(xattr_value, xattr_value_len);
rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data,
0, GFP_NOFS);
--
2.34.1
