Bug 1798

Summary: Add fsync() support to sftp/sftp-server
Product: Portable OpenSSH Reporter: Iain Morgan <imorgan>
Component: sftp-serverAssignee: Assigned to nobody <unassigned-bugs>
Status: CLOSED FIXED    
Severity: enhancement CC: daniel.subs, djm, rjones, tj
Priority: P2    
Version: -current   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 2130    
Attachments:
Description Flags
Initial implementation of the fsync@openssh.com extension
none
Correct return code from do_fsync() when server does not support the extension
none
Updated patch vs -current
none
Updated to -current none

Description Iain Morgan 2010-07-16 09:56:50 AEST 
Created attachment 1898 [details]
Initial implementation of the fsync@openssh.com extension

In some cases the delay between when a file has been transferred and
when the operating system actually flushes data to disk may provide an
opportunity for file loss or corruption. To address this, it would
be useful to call fsync(2) after writing a file.

The attached patch adds an fsync@openssh.com extension to sftp-server
which can be used to request that fsync(2) be called. In addition, a
-f option has been added to get/put and to the sftp command-line itself
to request local or remote fsync(2) of the written file.
Comment 1 Damien Miller 2010-07-19 13:22:23 AEST 
The diff looks good, I'll add this to the list for V_5_6
Comment 2 Iain Morgan 2010-07-20 05:36:40 AEST 
Created attachment 1905 [details]
Correct return code from do_fsync() when server does not support the extension
Comment 3 Damien Miller 2010-08-03 15:41:05 AEST 
We are freezing for the OpenSSH 5.6 release. Retargetting these bugs to the next release.
Comment 4 Damien Miller 2011-01-24 12:30:52 AEDT 
Retarget unclosed bugs from 5.7=>5.8
Comment 5 Iain Morgan 2011-07-16 06:44:59 AEST 
Created attachment 2065 [details]
Updated patch vs -current
Comment 6 Damien Miller 2011-09-06 10:34:22 AEST 
Retarget unresolved bugs/features to 6.0 release
Comment 7 Damien Miller 2011-09-06 10:36:33 AEST 
Retarget unresolved bugs/features to 6.0 release
Comment 8 Damien Miller 2011-09-06 10:39:09 AEST 
Retarget unresolved bugs/features to 6.0 release

(try again - bugzilla's "change several" isn't)
Comment 9 Damien Miller 2012-02-24 10:34:31 AEDT 
Retarget from 6.0 to 6.1
Comment 10 Damien Miller 2012-02-24 10:38:10 AEDT 
Retarget 6.0 => 6.1
Comment 11 Damien Miller 2012-09-07 11:38:22 AEST 
Retarget uncompleted bugs from 6.1 => 6.2
Comment 12 Damien Miller 2012-09-07 11:40:46 AEST 
Retarget bugs from 6.1 => 6.2
Comment 13 Damien Miller 2013-03-08 10:24:13 AEDT 
retarget to openssh-6.3
Comment 14 Richard W.M. Jones 2013-04-09 00:05:02 AEST 
I just came across this proposed extension of sftp in
OpenSSH, and it's something that we could really use
in order to make qemu ssh block device safe:

http://lists.nongnu.org/archive/html/qemu-devel/2013-04/msg01118.html
Comment 15 Richard W.M. Jones 2013-04-09 19:43:41 AEST 
I have now added support to libssh2 to support this call, and
also tested that it works (it does).

http://www.libssh2.org/mail/libssh2-devel-archive-2013-04/0007.shtml
http://www.libssh2.org/mail/libssh2-devel-archive-2013-04/0006.shtml
Comment 16 Damien Miller 2013-07-25 12:18:12 AEST 
Retarget to openssh-6.4
Comment 17 Damien Miller 2013-07-25 12:21:14 AEST 
Retarget 6.3 -> 6.4
Comment 18 Richard W.M. Jones 2013-07-25 18:16:16 AEST 
Why does this keep getting delayed?  Why not just add the patch?

It's a simple & useful feature which would allow qemu to use
OpenSSH.
Comment 19 Damien Miller 2013-10-11 14:23:14 AEDT 
Created attachment 2351 [details]
Updated to -current

Revised patch, with description of extension in the PROTOCOL file.

Hopefully I'll be able to get it in this time. I wasn't able to convince everyone that it was worth the DoS risk before (many platforms implement fsync() by just calling the fs-wide sync() function which can trigger a lot of I/O), but now we have the request blacklist that can avoid this in cases where users can't be trusted.
Comment 20 Daniel Black 2013-10-11 15:32:06 AEDT 
small doco error in PROTOCOL

339		string		"hardlink@openssh.com"
Comment 21 Damien Miller 2013-10-17 11:30:30 AEDT 
Committed - this will be in OpenSSH 6.4. Thanks!
Comment 22 Damien Miller 2016-08-02 10:42:50 AEST 
Close all resolved bugs after 7.3p1 release