From: Vivek Goyal <vgoyal@redhat.com>
Date: Fri, 9 Oct 2020 18:15:09 +0000 (-0400)
Subject: fuse: setattr should set FATTR_KILL_SUIDGID
X-Git-Tag: v5.11-rc1~84^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3179216135ec09825d7c7875580951a6e69dc5df;p=thirdparty%2Fkernel%2Flinux.git

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 c3e22a3dd3239..28b07ae5e55fd 100644
--- 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 2623c75b94a5c..9eb96e0564be1 100644
--- 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