On Fri, 2020-09-04 at 12:05 -0400, Jeff Layton wrote:
> 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@xxxxxxxxxx>
> ---
> fs/ceph/dir.c | 32 ++++++++++++++++---
> fs/ceph/inode.c | 82 +++++++++++++++++++++++++++++++++++++++----------
> fs/ceph/super.h | 3 ++
> 3 files changed, 96 insertions(+), 21 deletions(-)
>
FWIW, this patch is not working right, and I'm not sure why.
I've validated that I'm getting the same crypttext out
of fscrypt_encrypt_symlink that I'm feeding into fscrypt_get_symlink,
but the contents always look like gibberish in a readlink.
Did I make an obvious mistake somewhere?
> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> index 0ba17c592fe1..7ff8921dd3a7 100644
> --- a/fs/ceph/dir.c
> +++ b/fs/ceph/dir.c
> @@ -948,6 +948,7 @@ static int ceph_symlink(struct inode *dir, struct dentry *dentry,
> struct ceph_mds_client *mdsc = fsc->mdsc;
> 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;
>
> @@ -973,11 +974,33 @@ 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(BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);
> + if (!req->r_path2) {
> + err = -ENOMEM;
> + goto out_req;
> + }
> +
> + len = base64_encode_fname(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);
> @@ -997,6 +1020,7 @@ 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 e578e4cdcf30..dd39f886b03c 100644
> --- a/fs/ceph/inode.c
> +++ b/fs/ceph/inode.c
> @@ -14,6 +14,7 @@
> #include <linux/random.h>
> #include <linux/sort.h>
> #include <linux/iversion.h>
> +#include <linux/base64_fname.h>
>
> #include "super.h"
> #include "mds_client.h"
> @@ -33,8 +34,6 @@
> * (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);
>
> /*
> @@ -503,6 +502,7 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
> atomic64_set(&ci->i_complete_seq[0], 0);
> atomic64_set(&ci->i_complete_seq[1], 0);
> ci->i_symlink = NULL;
> + ci->i_symlink_len = 0;
>
> ci->i_max_bytes = 0;
> ci->i_max_files = 0;
> @@ -590,6 +590,7 @@ 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);
> }
>
> @@ -991,34 +992,60 @@ 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 = base64_decode_fname(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)
> + if (!ci->i_symlink) {
> ci->i_symlink = sym;
> - else
> + ci->i_symlink_len = symlen;
> + } else {
> kfree(sym); /* lost a race */
> + }
> + }
> +
> + 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;
> }
> - inode->i_link = ci->i_symlink;
> break;
> case S_IFDIR:
> inode->i_op = &ceph_dir_iops;
> @@ -2123,16 +2150,37 @@ 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 (inode->i_link)
> + return inode->i_link;
> +
> + if (!dentry)
> + return ERR_PTR(-ECHILD);
> +
> + return fscrypt_get_symlink(inode, ci->i_symlink, ci->i_symlink_len, 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 7c859824f64c..eea0ee17b747 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -344,6 +344,7 @@ struct ceph_inode_info {
> u64 i_max_bytes, i_max_files;
>
> s32 i_dir_pin;
> + u32 i_symlink_len;
>
> struct rb_root i_fragtree;
> int i_fragtree_nsplits;
> @@ -932,6 +933,8 @@ 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);
--
Jeff Layton <jlayton@xxxxxxxxxx>
