[PATCH 3.10 025/268] fs/cifs: make share unaccessible at root level mountable

Willy Tarreau
2017-06-19T18:34:32Z

From: Aurelien Aptel <aaptel@suse.com>

commit a6b5058fafdf508904bbf16c29b24042cef3c496 upstream.

if, when mounting //HOST/share/sub/dir/foo we can query /sub/dir/foo but
not any of the path components above:

- store the /sub/dir/foo prefix in the cifs super_block info
- in the superblock, set root dentry to the subpath dentry (instead of
the share root)
- set a flag in the superblock to remember it
- use prefixpath when building path from a dentry

fixes bso#8950

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
fs/cifs/cifs_fs_sb.h | 4 ++++
fs/cifs/cifsfs.c | 14 +++++++++++++-
fs/cifs/connect.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
fs/cifs/dir.c | 20 ++++++++++++++++++--
fs/cifs/inode.c | 22 ++++++++++++++++++++--
5 files changed, 104 insertions(+), 5 deletions(-)

diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index 37e4a72..ae4e35b 100644
--- a/fs/cifs/cifs_fs_sb.h
+++ b/fs/cifs/cifs_fs_sb.h
@@ -45,6 +45,9 @@
#define CIFS_MOUNT_POSIXACL 0x100000 /* mirror of MS_POSIXACL in mnt_cifs_flags */
#define CIFS_MOUNT_CIFS_BACKUPUID 0x200000 /* backup intent bit for a user */
#define CIFS_MOUNT_CIFS_BACKUPGID 0x400000 /* backup intent bit for a group */
+#define CIFS_MOUNT_USE_PREFIX_PATH 0x1000000 /* make subpath with unaccessible
+ * root mountable
+ */

struct cifs_sb_info {
struct rb_root tlink_tree;
@@ -65,5 +68,6 @@ struct cifs_sb_info {
char *mountdata; /* options received at mount time or via DFS refs */
struct backing_dev_info bdi;
struct delayed_work prune_tlinks;
+ char *prepath;
};
#endif /* _CIFS_FS_SB_H */
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 3752b9f..134607d 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -647,6 +647,14 @@ cifs_do_mount(struct file_system_type *fs_type,
goto out_cifs_sb;
}

+ if (volume_info->prepath) {
+ cifs_sb->prepath = kstrdup(volume_info->prepath, GFP_KERNEL);
+ if (cifs_sb->prepath == NULL) {
+ root = ERR_PTR(-ENOMEM);
+ goto out_cifs_sb;
+ }
+ }
+
cifs_setup_cifs_sb(volume_info, cifs_sb);

rc = cifs_mount(cifs_sb, volume_info);
@@ -685,7 +693,11 @@ cifs_do_mount(struct file_system_type *fs_type,
sb->s_flags |= MS_ACTIVE;
}

- root = cifs_get_root(volume_info, sb);
+ if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+ root = dget(sb->s_root);
+ else
+ root = cifs_get_root(volume_info, sb);
+
if (IS_ERR(root))
goto out_super;

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 0808b08..ece9071 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3430,6 +3430,44 @@ cifs_get_volume_info(char *mount_data, const char *devname)
return volume_info;
}

+static int
+cifs_are_all_path_components_accessible(struct TCP_Server_Info *server,
+ unsigned int xid,
+ struct cifs_tcon *tcon,
+ struct cifs_sb_info *cifs_sb,
+ char *full_path)
+{
+ int rc;
+ char *s;
+ char sep, tmp;
+
+ sep = CIFS_DIR_SEP(cifs_sb);
+ s = full_path;
+
+ rc = server->ops->is_path_accessible(xid, tcon, cifs_sb, "");
+ while (rc == 0) {
+ /* skip separators */
+ while (*s == sep)
+ s++;
+ if (!*s)
+ break;
+ /* next separator */
+ while (*s && *s != sep)
+ s++;
+
+ /*
+ * temporarily null-terminate the path at the end of
+ * the current component
+ */
+ tmp = *s;
+ *s = 0;
+ rc = server->ops->is_path_accessible(xid, tcon, cifs_sb,
+ full_path);
+ *s = tmp;
+ }
+ return rc;
+}
+
int
cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *volume_info)
{
@@ -3556,6 +3594,16 @@ remote_path_check:
kfree(full_path);
goto mount_fail_check;
}
+
+ rc = cifs_are_all_path_components_accessible(server,
+ xid, tcon, cifs_sb,
+ full_path);
+ if (rc != 0) {
+ cifs_dbg(VFS, "cannot query dirs between root and final path, "
+ "enabling CIFS_MOUNT_USE_PREFIX_PATH\n");
+ cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
+ rc = 0;
+ }
kfree(full_path);
}

@@ -3813,6 +3861,7 @@ cifs_umount(struct cifs_sb_info *cifs_sb)

bdi_destroy(&cifs_sb->bdi);
kfree(cifs_sb->mountdata);
+ kfree(cifs_sb->prepath);
unload_nls(cifs_sb->local_nls);
kfree(cifs_sb);
}
diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index a998c92..5431247 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -83,6 +83,7 @@ build_path_from_dentry(struct dentry *direntry)
struct dentry *temp;
int namelen;
int dfsplen;
+ int pplen = 0;
char *full_path;
char dirsep;
struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);
@@ -94,8 +95,12 @@ build_path_from_dentry(struct dentry *direntry)
dfsplen = strnlen(tcon->treeName, MAX_TREE_SIZE + 1);
else
dfsplen = 0;
+
+ if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+ pplen = cifs_sb->prepath ? strlen(cifs_sb->prepath) + 1 : 0;
+
cifs_bp_rename_retry:
- namelen = dfsplen;
+ namelen = dfsplen + pplen;
seq = read_seqbegin(&rename_lock);
rcu_read_lock();
for (temp = direntry; !IS_ROOT(temp);) {
@@ -136,7 +141,7 @@ cifs_bp_rename_retry:
}
}
rcu_read_unlock();
- if (namelen != dfsplen || read_seqretry(&rename_lock, seq)) {
+ if (namelen != dfsplen + pplen || read_seqretry(&rename_lock, seq)) {
cifs_dbg(FYI, "did not end path lookup where expected. namelen=%ddfsplen=%d\n",
namelen, dfsplen);
/* presumably this is only possible if racing with a rename
@@ -152,6 +157,17 @@ cifs_bp_rename_retry:
those safely to '/' if any are found in the middle of the prepath */
/* BB test paths to Windows with '/' in the midst of prepath */

+ if (pplen) {
+ int i;
+
+ cifs_dbg(FYI, "using cifs_sb prepath <%s>\n", cifs_sb->prepath);
+ memcpy(full_path+dfsplen+1, cifs_sb->prepath, pplen-1);
+ full_path[dfsplen] = '\\';
+ for (i = 0; i < pplen-1; i++)
+ if (full_path[dfsplen+1+i] == '/')
+ full_path[dfsplen+1+i] = CIFS_DIR_SEP(cifs_sb);
+ }
+
if (dfsplen) {
strncpy(full_path, tcon->treeName, dfsplen);
if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS) {
diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index 54304cc..971e7be 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -895,12 +895,29 @@ struct inode *cifs_root_iget(struct super_block *sb)
struct inode *inode = NULL;
long rc;
struct cifs_tcon *tcon = cifs_sb_master_tcon(cifs_sb);
+ char *path = NULL;
+ int len;
+
+ if ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH)
+ && cifs_sb->prepath) {
+ len = strlen(cifs_sb->prepath);
+ path = kzalloc(len + 2 /* leading sep + null */, GFP_KERNEL);
+ if (path == NULL)
+ return ERR_PTR(-ENOMEM);
+ path[0] = '/';
+ memcpy(path+1, cifs_sb->prepath, len);
+ } else {
+ path = kstrdup("", GFP_KERNEL);
+ if (path == NULL)
+ return ERR_PTR(-ENOMEM);
+ }

xid = get_xid();
+ convert_delimiter(path, CIFS_DIR_SEP(cifs_sb));
if (tcon->unix_ext)
- rc = cifs_get_inode_info_unix(&inode, "", sb, xid);
+ rc = cifs_get_inode_info_unix(&inode, path, sb, xid);
else
- rc = cifs_get_inode_info(&inode, "", NULL, sb, xid, NULL);
+ rc = cifs_get_inode_info(&inode, path, NULL, sb, xid, NULL);

if (!inode) {
inode = ERR_PTR(rc);
@@ -928,6 +945,7 @@ struct inode *cifs_root_iget(struct super_block *sb)
}

out:
+ kfree(path);
/* can not call macro free_xid here since in a void func
* TODO: This is no longer true
*/
--
2.8.0.rc2.1.gbe9624a