[PATCH v2 14/25] evm: add support for fscaps security hooks

Seth Forshee (DigitalOcean)
2024-02-21T21:25:06Z

Support the new fscaps security hooks by converting the vfs_caps to raw
xattr data and then handling them the same as other xattrs.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---
include/linux/evm.h | 39 +++++++++++++++++++++++++
security/integrity/evm/evm_main.c | 60 +++++++++++++++++++++++++++++++++++++++
2 files changed, 99 insertions(+)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index 36ec884320d9..aeb9ff52ad22 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -57,6 +57,20 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
{
return evm_inode_post_setxattr(dentry, acl_name, NULL, 0);
}
+extern int evm_inode_set_fscaps(struct mnt_idmap *idmap,
+ struct dentry *dentry,
+ const struct vfs_caps *caps, int flags);
+static inline int evm_inode_remove_fscaps(struct dentry *dentry)
+{
+ return evm_inode_set_fscaps(&nop_mnt_idmap, dentry, NULL, XATTR_REPLACE);
+}
+extern void evm_inode_post_set_fscaps(struct mnt_idmap *idmap,
+ struct dentry *dentry,
+ const struct vfs_caps *caps, int flags);
+static inline void evm_inode_post_remove_fscaps(struct dentry *dentry)
+{
+ return evm_inode_post_set_fscaps(&nop_mnt_idmap, dentry, NULL, 0);
+}

int evm_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr, struct xattr *xattrs,
@@ -164,6 +178,31 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
return;
}

+static inline int evm_inode_set_fscaps(struct mnt_idmap *idmap,
+ struct dentry *dentry,
+ const struct vfs_caps *caps, int flags)
+{
+ return 0;
+}
+
+static inline int evm_inode_remove_fscaps(struct dentry *dentry)
+{
+ return 0;
+}
+
+static inline void evm_inode_post_set_fscaps(struct mnt_idmap *idmap,
+ struct dentry *dentry,
+ const struct vfs_caps *caps,
+ int flags)
+{
+ return;
+}
+
+static inline void evm_inode_post_remove_fscaps(struct dentry *dentry)
+{
+ return;
+}
+
static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr,
struct xattr *xattrs,
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index cc7956d7878b..ecf4634a921a 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -805,6 +805,66 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
evm_update_evmxattr(dentry, xattr_name, NULL, 0);
}

+int evm_inode_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
+ const struct vfs_caps *caps, int flags)
+{
+ struct inode *inode = d_inode(dentry);
+ struct vfs_ns_cap_data nscaps;
+ const void *xattr_data = NULL;
+ int size = 0;
+
+ /* Policy permits modification of the protected xattrs even though
+ * there's no HMAC key loaded
+ */
+ if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
+ return 0;
+
+ if (caps) {
+ size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps, &nscaps,
+ sizeof(nscaps));
+ if (size < 0)
+ return size;
+ xattr_data = &nscaps;
+ }
+
+ return evm_protect_xattr(idmap, dentry, XATTR_NAME_CAPS, xattr_data, size);
+}
+
+void evm_inode_post_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
+ const struct vfs_caps *caps, int flags)
+{
+ struct inode *inode = d_inode(dentry);
+ struct vfs_ns_cap_data nscaps;
+ const void *xattr_data = NULL;
+ int size = 0;
+
+ if (!evm_revalidate_status(XATTR_NAME_CAPS))
+ return;
+
+ evm_reset_status(dentry->d_inode);
+
+ if (!(evm_initialized & EVM_INIT_HMAC))
+ return;
+
+ if (is_unsupported_fs(dentry))
+ return;
+
+ if (caps) {
+ size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps, &nscaps,
+ sizeof(nscaps));
+ /*
+ * The fscaps here should have been converted to an xattr by
+ * evm_inode_set_fscaps() already, so a failure to convert
+ * here is a bug.
+ */
+ if (WARN_ON_ONCE(size < 0))
+ return;
+ xattr_data = &nscaps;
+ }
+
+ evm_update_evmxattr(dentry, XATTR_NAME_CAPS, xattr_data, size);
+}
+
static int evm_attr_change(struct mnt_idmap *idmap,
struct dentry *dentry, struct iattr *attr)
{

--
2.43.0