[PATCH 23/36] ceph: create symlinks with encrypted and base64-encoded targets

Jeff Layton
2021-12-09T15:37:33Z

When creating symlinks in encrypted directories, encrypt and
base64-encode the target with the new inode's key before sending to the
MDS.

When filling a symlinked inode, base64-decode it into a buffer that
we'll keep in ci->i_symlink. When get_link is called, decrypt the buffer
into a new one that will hang off i_link.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/ceph/dir.c | 51 ++++++++++++++++++++---
fs/ceph/inode.c | 106 ++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 140 insertions(+), 17 deletions(-)

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index f8812c976ba0..bf686e4af27a 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -948,6 +948,40 @@ static int ceph_create(struct user_namespace *mnt_userns, struct inode *dir,
return ceph_mknod(mnt_userns, dir, dentry, mode, 0);
}

+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+static int prep_encrypted_symlink_target(struct ceph_mds_request *req, const char *dest)
+{
+ int err;
+ int len = strlen(dest);
+ struct fscrypt_str osd_link = FSTR_INIT(NULL, 0);
+
+ err = fscrypt_prepare_symlink(req->r_parent, dest, len, PATH_MAX, &osd_link);
+ if (err)
+ goto out;
+
+ err = fscrypt_encrypt_symlink(req->r_new_inode, dest, len, &osd_link);
+ if (err)
+ goto out;
+
+ req->r_path2 = kmalloc(FSCRYPT_BASE64URL_CHARS(osd_link.len) + 1, GFP_KERNEL);
+ if (!req->r_path2) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ len = fscrypt_base64url_encode(osd_link.name, osd_link.len, req->r_path2);
+ req->r_path2[len] = '\0';
+out:
+ fscrypt_fname_free_buffer(&osd_link);
+ return err;
+}
+#else
+static int prep_encrypted_symlink_target(struct ceph_mds_request *req, const char *dest)
+{
+ return -EOPNOTSUPP;
+}
+#endif
+
static int ceph_symlink(struct user_namespace *mnt_userns, struct inode *dir,
struct dentry *dentry, const char *dest)
{
@@ -979,14 +1013,21 @@ static int ceph_symlink(struct user_namespace *mnt_userns, struct inode *dir,
goto out_req;
}

- req->r_path2 = kstrdup(dest, GFP_KERNEL);
- if (!req->r_path2) {
- err = -ENOMEM;
- goto out_req;
- }
req->r_parent = dir;
ihold(dir);

+ if (IS_ENCRYPTED(req->r_new_inode)) {
+ err = prep_encrypted_symlink_target(req, dest);
+ if (err)
+ goto out_req;
+ } else {
+ req->r_path2 = kstrdup(dest, GFP_KERNEL);
+ if (!req->r_path2) {
+ err = -ENOMEM;
+ goto out_req;
+ }
+ }
+
set_bit(CEPH_MDS_R_PARENT_LOCKED, &req->r_req_flags);
req->r_dentry = dget(dentry);
req->r_num_caps = 2;
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 37cb0d334cf2..da242ff1756e 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -35,6 +35,7 @@
*/

static const struct inode_operations ceph_symlink_iops;
+static const struct inode_operations ceph_encrypted_symlink_iops;

static void ceph_inode_work(struct work_struct *work);

@@ -632,6 +633,7 @@ void ceph_free_inode(struct inode *inode)
#ifdef CONFIG_FS_ENCRYPTION
kfree(ci->fscrypt_auth);
#endif
+ fscrypt_free_inode(inode);
kmem_cache_free(ceph_inode_cachep, ci);
}

@@ -825,6 +827,33 @@ void ceph_fill_file_time(struct inode *inode, int issued,
inode, time_warp_seq, ci->i_time_warp_seq);
}

+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+static int decode_encrypted_symlink(const char *encsym, int enclen, u8 **decsym)
+{
+ int declen;
+ u8 *sym;
+
+ sym = kmalloc(enclen + 1, GFP_NOFS);
+ if (!sym)
+ return -ENOMEM;
+
+ declen = fscrypt_base64url_decode(encsym, enclen, sym);
+ if (declen < 0) {
+ pr_err("%s: can't decode symlink (%d). Content: %.*s\n", __func__, declen, enclen, encsym);
+ kfree(sym);
+ return -EIO;
+ }
+ sym[declen + 1] = '\0';
+ *decsym = sym;
+ return declen;
+}
+#else
+static int decode_encrypted_symlink(const char *encsym, int symlen, u8 **decsym)
+{
+ return -EOPNOTSUPP;
+}
+#endif
+
/*
* Populate an inode based on info from mds. May be called on new or
* existing inodes.
@@ -1058,26 +1087,39 @@ int ceph_fill_inode(struct inode *inode, struct page *locked_page,
inode->i_fop = &ceph_file_fops;
break;
case S_IFLNK:
- inode->i_op = &ceph_symlink_iops;
if (!ci->i_symlink) {
u32 symlen = iinfo->symlink_len;
char *sym;

spin_unlock(&ci->i_ceph_lock);

- if (symlen != i_size_read(inode)) {
- pr_err("%s %llx.%llx BAD symlink "
- "size %lld\n", __func__,
- ceph_vinop(inode),
- i_size_read(inode));
+ if (IS_ENCRYPTED(inode)) {
+ if (symlen != i_size_read(inode))
+ pr_err("%s %llx.%llx BAD symlink size %lld\n",
+ __func__, ceph_vinop(inode), i_size_read(inode));
+
+ err = decode_encrypted_symlink(iinfo->symlink, symlen, (u8 **)&sym);
+ if (err < 0) {
+ pr_err("%s decoding encrypted symlink failed: %d\n",
+ __func__, err);
+ goto out;
+ }
+ symlen = err;
i_size_write(inode, symlen);
inode->i_blocks = calc_inode_blocks(symlen);
- }
+ } else {
+ if (symlen != i_size_read(inode)) {
+ pr_err("%s %llx.%llx BAD symlink size %lld\n",
+ __func__, ceph_vinop(inode), i_size_read(inode));
+ i_size_write(inode, symlen);
+ inode->i_blocks = calc_inode_blocks(symlen);
+ }

- err = -ENOMEM;
- sym = kstrndup(iinfo->symlink, symlen, GFP_NOFS);
- if (!sym)
- goto out;
+ err = -ENOMEM;
+ sym = kstrndup(iinfo->symlink, symlen, GFP_NOFS);
+ if (!sym)
+ goto out;
+ }

spin_lock(&ci->i_ceph_lock);
if (!ci->i_symlink)
@@ -1085,7 +1127,17 @@ int ceph_fill_inode(struct inode *inode, struct page *locked_page,
else
kfree(sym); /* lost a race */
}
- inode->i_link = ci->i_symlink;
+
+ if (IS_ENCRYPTED(inode)) {
+ /*
+ * Encrypted symlinks need to be decrypted before we can
+ * cache their targets in i_link. Don't touch it here.
+ */
+ inode->i_op = &ceph_encrypted_symlink_iops;
+ } else {
+ inode->i_link = ci->i_symlink;
+ inode->i_op = &ceph_symlink_iops;
+ }
break;
case S_IFDIR:
inode->i_op = &ceph_dir_iops;
@@ -2133,6 +2185,29 @@ static void ceph_inode_work(struct work_struct *work)
iput(inode);
}

+static const char *ceph_encrypted_get_link(struct dentry *dentry, struct inode *inode,
+ struct delayed_call *done)
+{
+ struct ceph_inode_info *ci = ceph_inode(inode);
+
+ if (!dentry)
+ return ERR_PTR(-ECHILD);
+
+ return fscrypt_get_symlink(inode, ci->i_symlink, i_size_read(inode), done);
+}
+
+static int ceph_encrypted_symlink_getattr(struct user_namespace *mnt_userns,
+ const struct path *path, struct kstat *stat,
+ u32 request_mask, unsigned int query_flags)
+{
+ int ret;
+
+ ret = ceph_getattr(mnt_userns, path, stat, request_mask, query_flags);
+ if (ret)
+ return ret;
+ return fscrypt_symlink_getattr(path, stat);
+}
+
/*
* symlinks
*/
@@ -2143,6 +2218,13 @@ static const struct inode_operations ceph_symlink_iops = {
.listxattr = ceph_listxattr,
};

+static const struct inode_operations ceph_encrypted_symlink_iops = {
+ .get_link = ceph_encrypted_get_link,
+ .setattr = ceph_setattr,
+ .getattr = ceph_encrypted_symlink_getattr,
+ .listxattr = ceph_listxattr,
+};
+
int __ceph_setattr(struct inode *inode, struct iattr *attr, struct ceph_iattr *cia)
{
struct ceph_inode_info *ci = ceph_inode(inode);
--
2.33.1