[RFC PATCH v3 16/16] ceph: create symlinks with encrypted and base64-encoded targets

Jeff Layton
2020-09-14T19:17:57Z

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 | 32 +++++++++++++++++++---
fs/ceph/inode.c | 71 ++++++++++++++++++++++++++++++++++++++-----------
fs/ceph/super.h | 2 ++
3 files changed, 86 insertions(+), 19 deletions(-)

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index e9fdb9c07320..65d82ab239b2 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -928,6 +928,7 @@ static int ceph_symlink(struct inode *dir, struct dentry *dentry,
struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(dir->i_sb);
struct ceph_mds_request *req;
struct ceph_acl_sec_ctx as_ctx = {};
+ struct fscrypt_str osd_link = FSTR_INIT(NULL, 0);
umode_t mode = S_IFLNK | 0777;
int err;

@@ -953,11 +954,33 @@ static int ceph_symlink(struct inode *dir, struct dentry *dentry,
goto out_req;
}

- req->r_path2 = kstrdup(dest, GFP_KERNEL);
- if (!req->r_path2) {
- err = -ENOMEM;
- goto out_req;
+ if (IS_ENCRYPTED(req->r_new_inode)) {
+ int len = strlen(dest);
+
+ err = fscrypt_prepare_symlink(dir, dest, len, PATH_MAX, &osd_link);
+ if (err)
+ goto out_req;
+
+ err = fscrypt_encrypt_symlink(req->r_new_inode, dest, len, &osd_link);
+ if (err)
+ goto out_req;
+
+ req->r_path2 = kmalloc(FSCRYPT_BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);
+ if (!req->r_path2) {
+ err = -ENOMEM;
+ goto out_req;
+ }
+
+ len = fscrypt_base64_encode(osd_link.name, osd_link.len, req->r_path2);
+ req->r_path2[len] = '\0';
+ } else {
+ req->r_path2 = kstrdup(dest, GFP_KERNEL);
+ if (!req->r_path2) {
+ err = -ENOMEM;
+ goto out_req;
+ }
}
+
req->r_parent = dir;
set_bit(CEPH_MDS_R_PARENT_LOCKED, &req->r_req_flags);
req->r_dentry = dget(dentry);
@@ -977,6 +1000,7 @@ static int ceph_symlink(struct inode *dir, struct dentry *dentry,
if (err)
d_drop(dentry);
ceph_release_acl_sec_ctx(&as_ctx);
+ fscrypt_fname_free_buffer(&osd_link);
return err;
}

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 8e9fb1311bb8..4ac267cc9085 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -33,8 +33,6 @@
* (typically because they are in the message handler path).
*/

-static const struct inode_operations ceph_symlink_iops;
-
static void ceph_inode_work(struct work_struct *work);

/*
@@ -593,6 +591,7 @@ void ceph_free_inode(struct inode *inode)
struct ceph_inode_info *ci = ceph_inode(inode);

kfree(ci->i_symlink);
+ fscrypt_free_inode(inode);
kmem_cache_free(ceph_inode_cachep, ci);
}

@@ -996,26 +995,39 @@ 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)) {
+ /* Do base64 decode so that we get the right size (maybe?) */
+ err = -ENOMEM;
+ sym = kmalloc(symlen + 1, GFP_NOFS);
+ if (!sym)
+ goto out;
+
+ symlen = fscrypt_base64_decode(iinfo->symlink, symlen, sym);
+ /*
+ * i_size as reported by the MDS may be wrong, due to base64
+ * inflation and padding. Fix it up here.
+ */
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)
@@ -1023,7 +1035,18 @@ 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. Leave it blank for now.
+ */
+ inode->i_link = NULL;
+ 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;
@@ -2124,16 +2147,34 @@ 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, ksize(ci->i_symlink), done);
+}
+
/*
* symlinks
*/
-static const struct inode_operations ceph_symlink_iops = {
+const struct inode_operations ceph_symlink_iops = {
.get_link = simple_get_link,
.setattr = ceph_setattr,
.getattr = ceph_getattr,
.listxattr = ceph_listxattr,
};

+const struct inode_operations ceph_encrypted_symlink_iops = {
+ .get_link = ceph_encrypted_get_link,
+ .setattr = ceph_setattr,
+ .getattr = ceph_getattr,
+ .listxattr = ceph_listxattr,
+};
+
int __ceph_setattr(struct inode *inode, struct iattr *attr)
{
struct ceph_inode_info *ci = ceph_inode(inode);
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 5d5283552c03..d58296bd8235 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -939,6 +939,8 @@ struct ceph_mds_reply_dirfrag;
struct ceph_acl_sec_ctx;

extern const struct inode_operations ceph_file_iops;
+extern const struct inode_operations ceph_symlink_iops;
+extern const struct inode_operations ceph_encrypted_symlink_iops;

extern struct inode *ceph_alloc_inode(struct super_block *sb);
extern void ceph_evict_inode(struct inode *inode);
--
2.26.2