thr3ads.net - openssh unix dev - [Bug 2966] New: scp rev 1.202 fix doesn't quite hit the mark [Feb 2019]

If this information is useful, please help other people find it:
Share via:

bugzilla-daemon at bugzilla.mindrot.org

2019-Feb-08 16:23 UTC

[Bug 2966] New: scp rev 1.202 fix doesn't quite hit the mark

https://bugzilla.mindrot.org/show_bug.cgi?id=2966

            Bug ID: 2966
           Summary: scp rev 1.202 fix doesn't quite hit the mark
           Product: Portable OpenSSH
           Version: 7.9p1
          Hardware: Other
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: scp
          Assignee: unassigned-bugs at mindrot.org
          Reporter: norman at teach.cs.toronto.edu

Revision 1.202 to ssh/scp.c means to protect against a rogue
server that writes to unexpected file names, by checking that
the file name returned matches the original glob pattern.

The fix has two bugs:

1.  If the requested filename contains no / characters, e.g.

scp remote:'[xyz]*' .

or even

scp remote:safefile .

no check is done; the remote is permitted to send any file name
(hence overwrite any file) it likes.  The trouble is that the
new code does

        if ((restrict_pattern = strrchr(src_copy, '/')) != NULL) {
                *restrict_pattern++ = '\0';
        }

then, later,

        if (restrict_pattern != NULL &&
           fnmatch(restrict_pattern, cp, 0) != 0)
                SCREWUP("filename does not match request");

If there is no /, strrchr returns NULL, restrict_pattern is set
to NULL, and fnmatch is not called.

One simple fix might be:

        if ((restrict_pattern = strrchr(src_copy, '/')) != NULL) {
                *restrict_pattern++ = '\0';
        } else
                restrict_pattern = src_copy;

2.  Rather more subtly: before the fix, one could copy several
files while connecting and authenticating only once by doing

scp remote:'dir1/file1 dir2/file2 dir3/file3' .

or even

scp remote:'dir1/*.c dir2/*.[ch] dir3/*.o' .

Since the fix doesn't account for white space, it would
allow only file3 to be copied in the first case, and only
file names matching *.o (regardless of which directory they
came from) in the second.

One can quibble about whether multiple file names should
have been allowed like that in the first place, but it has
worked for a long time and some* have written scripts that
expect it.  More to the point, it makes the current fix
do the test wrong.

Fixing it to preserve the old behaviour seems worthwhile,
but adds complexity (I guess you'd need to allocate a
table to hold all the patterns, or just split remote
names into white-space-separated pieces at a much-higher
level in the code).  I can see the argument for not doing
that, or at least deferring it, since an insistent user
can use -T as a workaround.

But if the code isn't that white-space-aware, it should
at least check for and reject remote names containing
white space, since white space breaks the safety check.

Thanks,

Norman Wilson
Computer Science, University of Toronto

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

Mark D. Baushke

2019-Feb-08 16:38 UTC

head link

[Bug 2966] New: scp rev 1.202 fix doesn't quite hit the mark

Some filesystems have files with whitespace in the names which may
add an additional wrinkle to pattern matching fixes.

	-- Mark

bugzilla-daemon at bugzilla.mindrot.org

2019-Feb-11 06:34 UTC

head link

[Bug 2966] scp rev 1.202 fix doesn't quite hit the mark

https://bugzilla.mindrot.org/show_bug.cgi?id=2966

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
Thanks - the changes in rev 1.202 weren't complete, e.g. they don't
include support for {foo,bar} alternations. I've committed a fix that
also corrected the paths-without-slash problem along the way.

I'll take a look at the space-separated path thing; it might be
difficult to discern a space-separated source path that refers to
multiple files from one that refers to a single file with spaces in its
name. It really depends on the server's rules, and the client has no
way of knowing these.

In practice, /bin/sh is likely to be doing the dequoting/expansion,
except when it isn't.

-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.

bugzilla-daemon at bugzilla.mindrot.org

2019-Apr-04 22:37 UTC

head link

[Bug 2966] scp rev 1.202 fix doesn't quite hit the mark

https://bugzilla.mindrot.org/show_bug.cgi?id=2966

Jordan <jborean93 at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jborean93 at gmail.com

--- Comment #2 from Jordan <jborean93 at gmail.com> ---
Just to add a bit more to this problem, I've found that using single
quotes for the path component also causes it to fail with 'filename
does not match request'. For example If I was to do;

    scp -o User=username "[host]:'/tmp/file.txt'"

or even

    scp -o User=username
'[host]:'"'"'/tmp/file.txt'"'"''

It will fail with

    protocol error: filename does not match request

This worked perfectly fine before this patch and I don't see a reason
why it shouldn't continue to work going forward. Quotes aren't used all
the time but if the path we are trying to fetch has a space it is
needed. We also use single quotes so we don't have to escape any
metachars, e.g.

    scp -o User=username '[host]:'"'"'/tmp/file
$TERM.txt'"'"''

Would fetch the literal path '/tmp/file $TERM.txt' and not expand
$TERM. An alternate way would be to escape paths and meta chars with
'\' but that seems to be dependent on the shell used on the remote and
potentially fraught with danger. Being able to just enclose the path
with a single quote is a lot simpler.

https://github.com/ansible/ansible/issues/52640 has some more issues
and how we came across this problem.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

bugzilla-daemon at bugzilla.mindrot.org

2019-Apr-05 16:32 UTC

head link

[Bug 2966] scp client-side filename matching problems

https://bugzilla.mindrot.org/show_bug.cgi?id=2966

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|scp rev 1.202 fix doesn't   |scp client-side filename
                   |quite hit the mark          |matching problems

--- Comment #3 from Damien Miller <djm at mindrot.org> ---
I honestly don't know how far we're willing to chase this down in scp -
these are all extremely fiddly and easy to get wrong in the client.

To do it right means basically having to re-implement the entirety of
shell quote handling in scp. Even then, it all goes out the window if
the server happens to be using a different shell. 

In any case, it's too late to get fixes for this into OpenSSH 8.0. I
suggest adjusting your workflows to use sftp or otherwise using the new
scp -T flag to disable the extra client-side checking.

-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.

bugzilla-daemon at bugzilla.mindrot.org

2019-Apr-05 16:33 UTC

head link

[Bug 2966] scp client-side filename matching problems

https://bugzilla.mindrot.org/show_bug.cgi?id=2966

--- Comment #4 from Damien Miller <djm at mindrot.org> ---
I honestly don't know how far we're willing to chase this down in scp -
these are all extremely fiddly and easy to get wrong in the client.

To do it right means basically having to re-implement the entirety of
shell quote handling in scp. Even then, it all goes out the window if
the server happens to be using a different shell. 

In any case, it's too late to get fixes for this into OpenSSH 8.0. I
suggest adjusting your workflows to use sftp or otherwise using the new
scp -T flag to disable the extra client-side checking.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

bugzilla-daemon at bugzilla.mindrot.org

2019-Sep-26 09:56 UTC

head link