openssh unix dev - Apr 2022 - Portable OpenSSH on Linux: confusing error message with scp

Hi,

With OpenSSH 8.9p1 (and earlier) and scp server-side on Linux 5.13,
one gets a very confusing error message when the target directory ends
with / and *does not exist*:

	% scp /etc/issue localhost:/usr/foobar/
	scp: /usr/foobar/: Is a directory

stracing shows:

[pid 32671] stat("/usr/foobar/", 0x7fff4aaa5fd0) = -1 ENOENT (No such
file or directory)
[pid 32671] openat(AT_FDCWD, "/usr/foobar/", O_WRONLY|O_CREAT, 0644) =
-1 EISDIR (Is a directory)

scp.c does rougly:

                exists = stat(np, &stb) == 0;
                /* ... stuff elided ... */
                if ((ofd = open(np, O_WRONLY|O_CREAT, mode)) == -1) {
bad:                    run_err("%s: %s", np, strerror(errno));
                        continue;
                }

open(2) says:

       EISDIR pathname refers to a directory and the access requested involved
              writing (that is, O_WRONLY or O_RDWR is set).

Apparently, on OpenBSD it prints "No such file or directory" instead.

I wonder if adding

		if (errno == EISDIR)
			errno = ENOENT;

would be a suitable override, or perhaps you have a better idea.
But printing something is directory when it isn't is confusing. :)

cu,
-- 
Leah Neukirchen  <leah at vuxu.org>  https://leahneukirchen.org/

On Tue, 5 Apr 2022, Leah Neukirchen wrote:
> scp.c does rougly:
> 
>                 exists = stat(np, &stb) == 0;
>                 /* ... stuff elided ... */
>                 if ((ofd = open(np, O_WRONLY|O_CREAT, mode)) == -1) {
> bad:                    run_err("%s: %s", np, strerror(errno));
>                         continue;
>                 }
> would be a suitable override, or perhaps you have a better idea.
Without looking at the code (asking the Linux kernel developers to
fix their errno? probably doesn?t have a chance), maybe:

		nexists = stat(np, &stb) ? errno : 0;
		/*?*/
		if (nexists ||
		    (ofd = open(np, O_WRONLY|O_CREAT, mode)) == -1) {
			run_err("%s: %s", np,
			    strerror(nexists ? nexists : errno));
			continue;
		}
(and do something about that bad label)

Or even:
		if (!(exists = stat(np, &stb) == 0))
			goto bad;
		/*? rest as above */
But only if that elided stuff isn?t important. If it is, maybe:

		nexists = stat(np, &stb) ? errno : 0;
		/*?*/
		if ((ofd = open(np, O_WRONLY|O_CREAT, mode)) == -1) {
			run_err("%s: %s", np,
			    strerror(nexists ? nexists : errno));
			continue;
		}

Just a shoot into the blue that came to me while reading the mail.

bye,
//mirabilos
-- 
Sometimes they [people] care too much: pretty printers [and syntax highligh-
ting, d.A.] mechanically produce pretty output that accentuates irrelevant
detail in the program, which is as sensible as putting all the prepositions
in English text in bold font.	-- Rob Pike in "Notes on Programming in
C"

On 4/5/22 22:14, Leah Neukirchen wrote:
> Hi,
> 
> With OpenSSH 8.9p1 (and earlier) and scp server-side on Linux 5.13,
> one gets a very confusing error message when the target directory ends
> with / and *does not exist*:
> 
> 	% scp /etc/issue localhost:/usr/foobar/
> 	scp: /usr/foobar/: Is a directory
> 
> stracing shows:
> 
> [pid 32671] stat("/usr/foobar/", 0x7fff4aaa5fd0) = -1 ENOENT (No
such file or directory)
> [pid 32671] openat(AT_FDCWD, "/usr/foobar/", O_WRONLY|O_CREAT,
0644) = -1 EISDIR (Is a directory)
> 
> scp.c does rougly:
> 
>                  exists = stat(np, &stb) == 0;
>                  /* ... stuff elided ... */
>                  if ((ofd = open(np, O_WRONLY|O_CREAT, mode)) == -1) {
> bad:                    run_err("%s: %s", np, strerror(errno));
>                          continue;
>                  }
> 
> open(2) says:
> 
>         EISDIR pathname refers to a directory and the access requested
involved
>                writing (that is, O_WRONLY or O_RDWR is set).
> 
> Apparently, on OpenBSD it prints "No such file or directory"
instead.
> 
> I wonder if adding
> 
> 		if (errno == EISDIR)
> 			errno = ENOENT;
> 
> would be a suitable override, or perhaps you have a better idea.
> But printing something is directory when it isn't is confusing. :)
> 
> cu,
This was first reported in 2010 as far as I know and it was one of the 
first issues I was trying to fix in OpenSSH:

https://bugzilla.mindrot.org/show_bug.cgi?id=1768

Unfortunately, without any answer from the OpenSSH developers for almost 
12 years. From time to time, somebody runs into this issue, complains 
but nothing really changed.

Hope it helps,
-- 
Jakub Jelen
Crypto Team, Security Engineering
Red Hat, Inc.