Bug 208965

Summary:	extattr(2) doesn't allow attribute names of length EXTATTR_MAXNAMELEN
Product:	Base System	Reporter:	Alan Somers <asomers>
Component:	kern	Assignee:	Conrad Meyer <cem>
Status:	Closed FIXED
Severity:	Affects Many People	CC:	amd64, ngie
Priority:	---	Keywords:	patch
Version:	CURRENT
Hardware:	Any
OS:	Any

Description Alan Somers freebsd_committer

2016-04-21 22:21:20 UTC

extattr(2) claims that attribute names may be up to EXTATTR_MAXNAMELEN in length.  However, in practice it only allows attribute names of up to EXTATTR_MAXNAMELEN - 1.

[alans@alans-fbsd-head2 /tmp]$ touch foo
[alans@alans-fbsd-head2 /tmp]$ ATTRNAME=`jot -b X -s "" 255 0`
[alans@alans-fbsd-head2 /tmp]$ setextattr user $ATTRNAME myvalue foo
setextattr: foo: failed: File name too long

Comment 1 Enji Cooper freebsd_committer

2016-04-21 22:27:28 UTC

(related to https://reviews.freebsd.org/D5889).

Comment 2 Conrad Meyer freebsd_committer

2020-04-27 02:02:55 UTC

I believe this is due to copyinstr(), which works with NUL-terminated strings (and lengths), while the stack buffer in sys_extattr_set_fd(), etc, are only sized to EXTATTR_MAXNAMELEN.  To fix this I think we just need to size the buffers one larger to allow for the trailing NUL copyinstr expects.

Comment 3 Conrad Meyer freebsd_committer

2020-04-27 02:14:31 UTC

FWIW, UFS_EXTATTR only disables the crummy extattrs in UFS1.  UFS2 extattrs are not controlled by that knob.

https://reviews.freebsd.org/D24584 is a proposed patch; it compiles but I have not tested it.

Comment 4 commit-hook freebsd_committer

2020-05-14 03:02:05 UTC

A commit references this bug:

Author: cem
Date: Thu May 14 03:01:24 UTC 2020
New revision: 361021
URL: https://svnweb.freebsd.org/changeset/base/361021

Log:
  vfs_extattr: Allow extattr names up to the full max

  Extattr names are allowed to be 255 bytes -- not 254 bytes plus trailing
  NUL.  Provide a 256 buffer so that copyinstr() has room for the trailing
  NUL.

  Re-enable test for maximal name lengths.

  PR:		208965
  Reported by:	asomers
  Reviewed by:	asomers
  Differential Revision:	https://reviews.freebsd.org/D24584

Changes:
  head/sys/kern/vfs_extattr.c
  head/usr.sbin/extattr/tests/extattr_test.sh