fuse: setattr should set FATTR_KILL_SUIDGID

If fc->handle_killpriv_v2 is enabled, we expect file server to clear
suid/sgid/security.capbility upon chown/truncate/write as appropriate.

Upon truncate (ATTR_SIZE), suid/sgid are cleared only if caller does not
have CAP_FSETID.  File server does not know whether caller has CAP_FSETID
or not.  Hence set FATTR_KILL_SUIDGID upon truncate to let file server know
that caller does not have CAP_FSETID and it should kill suid/sgid as
appropriate.

On chown (ATTR_UID/ATTR_GID) suid/sgid need to be cleared irrespective of
capabilities of calling process, so set FATTR_KILL_SUIDGID unconditionally
in that case.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index c3e22a3..28b07ae 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1648,10 +1648,20 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
                inarg.valid |= FATTR_FH;
                inarg.fh = ff->fh;
        }
+
+       /* Kill suid/sgid for non-directory chown unconditionally */
+       if (fc->handle_killpriv_v2 && !S_ISDIR(inode->i_mode) &&
+           attr->ia_valid & (ATTR_UID | ATTR_GID))
+               inarg.valid |= FATTR_KILL_SUIDGID;
+
        if (attr->ia_valid & ATTR_SIZE) {
                /* For mandatory locking in truncate */
                inarg.valid |= FATTR_LOCKOWNER;
                inarg.lock_owner = fuse_lock_owner_id(fc, current->files);
+
+               /* Kill suid/sgid for truncate only if no CAP_FSETID */
+               if (fc->handle_killpriv_v2 && !capable(CAP_FSETID))
+                       inarg.valid |= FATTR_KILL_SUIDGID;
        }
        fuse_setattr_fill(fc, &args, inode, &inarg, &outarg);
        err = fuse_simple_request(fm, &args);

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 2623c75..9eb96e0 100644 (file)
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -177,7 +177,7 @@
  *  - add flags to fuse_attr, add FUSE_ATTR_SUBMOUNT, add FUSE_SUBMOUNTS
  *
  *  7.33
- *  - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID
+ *  - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID
  */
 
 #ifndef _LINUX_FUSE_H
@@ -274,6 +274,7 @@ struct fuse_file_lock {
 #define FATTR_MTIME_NOW        (1 << 8)
 #define FATTR_LOCKOWNER        (1 << 9)
 #define FATTR_CTIME    (1 << 10)
+#define FATTR_KILL_SUIDGID     (1 << 11)
 
 /**
  * Flags returned by the OPEN request