ext4 crypto: revalidate dentry after adding or removing the key

Add a validation check for dentries for encrypted directory to make
sure we're not caching stale data after a key has been added or removed.

Also check to make sure that status of the encryption key is updated
when readdir(2) is executed.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

4 files changed, 81 insertions, 0 deletions

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index c8021208a7eb..38f7562489bb 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -467,3 +467,59 @@ uint32_t ext4_validate_encryption_key_size(uint32_t mode, uint32_t size)
                 return size;
         return 0;
 }
+
+/*
+ * Validate dentries for encrypted directories to make sure we aren't
+ * potentially caching stale data after a key has been added or
+ * removed.
+ */
+static int ext4_d_revalidate(struct dentry *dentry, unsigned int flags)
+{
+        struct inode *dir = d_inode(dentry->d_parent);
+        struct ext4_crypt_info *ci = EXT4_I(dir)->i_crypt_info;
+        int dir_has_key, cached_with_key;
+
+        if (!ext4_encrypted_inode(dir))
+                return 0;
+
+        if (ci && ci->ci_keyring_key &&
+            (ci->ci_keyring_key->flags & ((1 << KEY_FLAG_INVALIDATED) |
+                                          (1 << KEY_FLAG_REVOKED) |
+                                          (1 << KEY_FLAG_DEAD))))
+                ci = NULL;
+
+        /* this should eventually be an flag in d_flags */
+        cached_with_key = dentry->d_fsdata != NULL;
+        dir_has_key = (ci != NULL);
+
+        /*
+         * If the dentry was cached without the key, and it is a
+         * negative dentry, it might be a valid name.  We can't check
+         * if the key has since been made available due to locking
+         * reasons, so we fail the validation so ext4_lookup() can do
+         * this check.
+         *
+         * We also fail the validation if the dentry was created with
+         * the key present, but we no longer have the key, or vice versa.
+         */
+        if ((!cached_with_key && d_is_negative(dentry)) ||
+            (!cached_with_key && dir_has_key) ||
+            (cached_with_key && !dir_has_key)) {
+#if 0                           /* Revalidation debug */
+                char buf[80];
+                char *cp = simple_dname(dentry, buf, sizeof(buf));
+
+                if (IS_ERR(cp))
+                        cp = (char *) "???";
+                pr_err("revalidate: %s %p %d %d %d\n", cp, dentry->d_fsdata,
+                       cached_with_key, d_is_negative(dentry),
+                       dir_has_key);
+#endif
+                return 0;
+        }
+        return 1;
+}
+
+const struct dentry_operations ext4_encrypted_d_ops = {
+        .d_revalidate = ext4_d_revalidate,
+};
diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 1d1bca74f844..6d17f31a31d7 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -111,6 +111,12 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
         int dir_has_error = 0;
         struct ext4_str fname_crypto_str = {.name = NULL, .len = 0};
 
+        if (ext4_encrypted_inode(inode)) {
+                err = ext4_get_encryption_info(inode);
+                if (err && err != -ENOKEY)
+                        return err;
+        }
+
         if (is_dx_dir(inode)) {
                 err = ext4_dx_readdir(file, ctx);
                 if (err != ERR_BAD_DX_DIR) {
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0662b285dc8a..157b458a69d4 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2302,6 +2302,7 @@ struct page *ext4_encrypt(struct inode *inode,
 int ext4_decrypt(struct page *page);
 int ext4_encrypted_zeroout(struct inode *inode, ext4_lblk_t lblk,
                            ext4_fsblk_t pblk, ext4_lblk_t len);
+extern const struct dentry_operations ext4_encrypted_d_ops;
 
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 int ext4_init_crypto(void);
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 06574dd77614..5de8483f0062 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1558,6 +1558,24 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, unsi
         struct ext4_dir_entry_2 *de;
         struct buffer_head *bh;
 
+       if (ext4_encrypted_inode(dir)) {
+               int res = ext4_get_encryption_info(dir);
+
+                /*
+                 * This should be a properly defined flag for
+                 * dentry->d_flags when we uplift this to the VFS.
+                 * d_fsdata is set to (void *) 1 if if the dentry is
+                 * created while the directory was encrypted and we
+                 * don't have access to the key.
+                 */
+               dentry->d_fsdata = NULL;
+               if (ext4_encryption_info(dir))
+                       dentry->d_fsdata = (void *) 1;
+               d_set_d_op(dentry, &ext4_encrypted_d_ops);
+               if (res && res != -ENOKEY)
+                       return ERR_PTR(res);
+       }
+
         if (dentry->d_name.len > EXT4_NAME_LEN)
                 return ERR_PTR(-ENAMETOOLONG);