Bug 1120

Summary:	sftp deletes files if destination==source and client==server
Product:	Portable OpenSSH	Reporter:	1useaccount_84
Component:	sftp	Assignee:	Assigned to nobody <unassigned-bugs>
Status:	CLOSED WONTFIX
Severity:	enhancement
Priority:	P5
Version:	3.9p1
Hardware:	ix86
OS:	Linux

Description 1useaccount_84 2005-11-18 04:37:22 AEDT

If one inadvertently does a "self-connection" (i.e., from the client machine "mymachine" types "sftp mymachine"), logs in, and then "put foo", sftp transfers the file foo **leaving it empty** (0 bytes), therefore producing data loss.

Maybe it is easier with an example:
++++++++++++++++++++++++++++++++++++++++++++
user@mymachine:~$ ls -l foo
-rw-rw-r--  1 user user 550 Nov 17 18:29 foo
user@mymachine:~$ sftp mymachine
Connecting to mymachine...
user@mymachine's password:
sftp> put foo
Uploading foo to /home/user/foo
foo                                             0%    0     0.0KB/s   --:-- ETA
sftp> quit
user@mymachine:~$ ls -l foo
-rw-rw-r--  1 user user 0 Nov 17 18:30 foo
+++++++++++++++++++++++++++++++++++++++++++++

Comment 1 Frank Cusack 2005-11-18 05:14:14 AEDT

How is this a bug???  It's like saying 'cp foo foo' is a bug.  I guess the server
side could write to a tmp file (like rsync would do), but severity seems like
it should be trivial at best

Comment 2 Damien Miller 2005-11-23 22:28:54 AEDT

writing to a temp file and doing an atomic replace changes the semantics on transfer a bit, but I am not sure it matters much. This certainly is not a critical bug.

Comment 3 1useaccount_84 2005-11-24 03:11:46 AEDT

Well, IMHO it *is* a critical bug since there is data loss (actually, I lost some critical info that luckily was partially backed up).

Note that it is different from "cp foo foo" (in my case at least): cp complains that destination is the same as source and does nothing. 
It is also different from "scp foo mymachine:foo" since scp "copies" foo but leaves it untouched (not with 0 bytes as sftp does).

I am reseting the severity back to "critical" for that reason, but I will accept your final word if you still think that I am wrong (and hence you revert it to "enhancement" again).

Comment 4 Darren Tucker 2005-11-24 13:45:52 AEDT

Also "cp foo foo" can check the inode numbers to see if they're the same file (or different hard links to the same file), whereas sftp can't.

A better example would be "cat <foo >foo"; that'll trash the source file on most systems.  Welcome to Unix.

Writing to a tempfile and doing an atomic rename will mean that you will use up to twice the storage during the transfer, too.

Comment 5 Damien Miller 2006-04-18 14:45:35 AEST

wontfix - generally, it is impossible to detect this reliably. Just don't do it.

Comment 6 Darren Tucker 2006-10-07 11:43:14 AEST

Change all RESOLVED bug to CLOSED with the exception of the ones fixed post-4.4.