bugGNU Wget - Bugs: bug #60494, Percent character in filename gets...

 
 

bug #60494: Percent character in filename gets escaped twice

Submitter:  None
Submitted:  Sat 01 May 2021 04:53:06 PM UTC
   
 
Category:  Program Logic Severity:  3 - Normal
Priority:  5 - Normal Status:  None
Privacy:  Public Assigned to:  None
Originator Name:  Ed Grochowski Originator Email:  -email is unavailable-
Open/Closed:  Open Release:  trunk
Operating System:  GNU/Linux Reproducibility:  Every Time
Fixed Release:  None Planned Release:  None
Regression:  None Work Required:  None
Patch Included:  No
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Sat 22 May 2021 12:41:04 PM UTC, comment #8: 

So what KodeCharlie says is correct (regarding b)).
I would reword it like: We have arbitrary user input which has nothing to do what RFCs say. And this is the hard part as we have to 'guess' what the user meant.
Once the input is 'normalized' (unescaped, charset translated (into utf-8), protcoll extended, ...), the rest is straight forward following the RFCs.

@PetrPisar Regarding the filename: it is also user input. And the problem is that the wget author(s) made some decisions in the past on how to treat user input. There is no black and white here and any decision has it's pros and cons.
I think that part of the problem is that URLs on web sites are often printed in their escaped form. And wget users explicitly wanted to use copy&paste (from web site to console).

Then the next aspect is: we don't want to change a long-standing (default) behavior. This breaks (production) scripts and command lines. What we can possibly do is to add a new '--strict-input' option that skips 'guessing' and instead assumes a 100% valid URL. BTW, this is a good idea for wget2 ;-)

I agree that "wget [option]... [URL]..." is not 100% correct in terms of RFCs. But wget is also a user tool, and normal users don't have the RFCs in mind when they think about URLs.


Tim Ruehsen <rockdaboot>
Group administrator
Sun 16 May 2021 08:18:45 PM UTC, comment #7: 

My $0.02:  there's (a) the specification, and then there's (b) the reality of what's out there in the wild.  Inline docs for wget make it clear that at least part of the logic is concerned with (b).

An inefficient but possibly easy fix to this bug might simply be to make a deep copy of the struct url each time url_escape() is called. This issue, after all, has grown out of an optimization (ie, in-place string-edits) that isn't working quite as expected.

Kode Charlie <kodecharlie>
Sun 16 May 2021 03:59:57 PM UTC, comment #6: 

You cannot state a question like that because a random string is ambiguous by it's nature.

According to the specification <https://datatracker.ietf.org/doc/html/rfc3986#section-2.4> there is nothing as an unescaped URI. URI is always escaped by the definition.

Look at the original report: You have a file name "qtwebengine-everywhere-src-5.15.2-%231904652.patch.gz". It's a file name. Not an URI. If you construct a URL for the file name using an "https://mirrors.slackware.com/slackware/slackware64-current/source/l/qt5/patches/" base URL, then you need to escape the file name string and then append it it after a path delimiter of the base URL. I.e. you convert the file name to "qtwebengine-everywhere-src-5.15.2-%25231904652.patch.gz" and then append it to the base resulting into "https://mirrors.slackware.com/slackware/slackware64-current/source/l/qt5/patches/qtwebengine-everywhere-src-5.15.2-%25231904652.patch.gz" URL. This URL is passed to to wget command. Thus wget should not escape it again. It could validate and report an error. But not escape it.

I will quote the specification here:

   Under normal circumstances, the only time when octets within a URI
   are percent-encoded is during the process of producing the URI from
   its component parts.  This is when an implementation determines which
   of the reserved characters are to be used as subcomponent delimiters
   and which can be safely used as data.  Once produced, a URI is always
   in its percent-encoded form.

Please, pay attention to the last sentence.

Of course wget could state that its argument is a byte stream without any other constrains. But a manual of wget(1) reads something different, it states it's a URL:

SYNOPSIS
       wget [option]... [URL]...

Hence wget should not attempt any escaping.

Petr Pisar <petrp>
Sun 16 May 2021 03:00:43 PM UTC, comment #5: 

The main Q is how does Wget know if the input URL is already escaped or not ?

Did you read this comment ?
https://gitlab.com/gnuwget/wget/-/blob/master/src/url.c#L329

Tim Ruehsen <rockdaboot>
Group administrator
Sat 15 May 2021 07:05:05 PM UTC, comment #4: 

Here's one proposed change (see patch below).  It likely is not comprehensive enough. 

The broader issue seems to be that there are circumstances in ./src/retr.c when retrieve_url() calls url_parse(), which already was called in ./src/main.c.  This can result in the file property in struct url being modified in-place more than once (triggering errors as the one originally reported in this issue).

For now, I'm going to defer making these changes (including suggested patch below) to those more familiar with the wget repo than I.


diff --git a/src/http.c b/src/http.c
index d25762fa..a9fa237f 100644
--- a/src/http.c
+++ b/src/http.c
@@ -4280,8 +4280,10 @@ http_loop (const struct url *u, struct url *original_url, char **newloc,
     }
   else if (!opt.content_disposition)
     {
-      hstat.local_file =
-        url_file_name (opt.trustservernames ? u : original_url, NULL);
+      if (opt.trustservernames)
+        hstat.local_file = url_file_name (u, NULL);
+      else
+        hstat.local_file = original_url->file;
       got_name = true;
     }


Kode Charlie <kodecharlie>
Sat 15 May 2021 04:15:11 PM UTC, comment #3: 

I have an explanation but as yet, no fix.

In ./src/url.c, the routine url_unescape() is called twice for the same path component (ie, the basename).  Since url_unescape_1() modifies the path component in-place, the effect of processing:

qtwebengine-everywhere-src-5.15.2-%25231904652.patch.gz

twice is that after the first pass, the substring %2523 is converted to %23, and then after the second pass to #.

Hence, the resulting filename:

qtwebengine-everywhere-src-5.15.2-#1904652.patch.gz


I'm looking into a fix.

Kode Charlie <kodecharlie>
Sat 15 May 2021 11:58:38 AM UTC, comment #2: 

Correction: based on debug-logs, quoted logic does seem ok. I am looking into other logic before convert_fname() (which calls iconv()) is called.

comment #1:

> system: macOS Big Sur v. 11.2.3
> wget: master branch
>
> Offending logic from ./src/url.c is shown below. I believe the issue is in iconv().
>


>       if (iconv (cd, (ICONV_CONST char **) &fname, &inlen, &s, &outlen) == 0
>           && iconv (cd, NULL, NULL, &s, &outlen) == 0)
>         {
>           *(converted_fname + len - outlen - done) = '\0';
>           iconv_close (cd);
>           DEBUGP (("Converted file name '%s' (%s) -> '%s' (%s)\n",
>                    orig_fname, from_encoding, converted_fname, to_encoding));
>           xfree (orig_fname);
>           return converted_fname;
>         }


Kode Charlie <kodecharlie>
Sat 15 May 2021 11:34:42 AM UTC, comment #1: 

system: macOS Big Sur v. 11.2.3
wget: master branch

Offending logic from ./src/url.c is shown below. I believe the issue is in iconv().


      if (iconv (cd, (ICONV_CONST char **) &fname, &inlen, &s, &outlen) == 0
          && iconv (cd, NULL, NULL, &s, &outlen) == 0)
        {
          *(converted_fname + len - outlen - done) = '\0';
          iconv_close (cd);
          DEBUGP (("Converted file name '%s' (%s) -> '%s' (%s)\n",
                   orig_fname, from_encoding, converted_fname, to_encoding));
          xfree (orig_fname);
          return converted_fname;
        }


Kode Charlie <kodecharlie>
Sat 01 May 2021 04:53:06 PM UTC, original submission:  

On Slackware64-current, the repository has a file whose name contains a percent character.  The original name is qtwebengine-everywhere-src-5.15.2-%231904652.patch.gz

When I download this file with wget 1.21.1, the saved filename is wrong.  The percent character is being escaped twice, once correctly and a second time superfluously.

% wget https://mirrors.slackware.com/slackware/slackware64-current/source/l/qt5/patches/qtwebengine-everywhere-src-5.15.2-%25231904652.patch.gz
--2021-04-30 16:31:02--  https://mirrors.slackware.com/slackware/slackware64-current/source/l/qt5/patches/qtwebengine-everywhere-src-5.15.2-%25231904652.patch.gz
Resolving mirrors.slackware.com (mirrors.slackware.com)... 207.223.116.213
Connecting to mirrors.slackware.com (mirrors.slackware.com)|207.223.116.213|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1653 (1.6K) [application/x-gzip]
Saving to: ‘qtwebengine-everywhere-src-5.15.2-#1904652.patch.gz’

qtwebengine-everywh 100%[===================>]   1.61K  --.-KB/s    in 0s     

2021-04-30 16:31:02 (676 MB/s) - ‘qtwebengine-everywhere-src-5.15.2-#1904652.patch.gz’ saved [1653/1653]

% ls -l
total 4
-rw-r--r-- 1 ed users 1653 Feb  8 13:44 qtwebengine-everywhere-src-5.15.2-#1904652.patch.gz

Anonymous

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

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Attached Files
file #51350:  wget-debug.txt added by None (2KiB - text/plain)

 

Depends on the following items: None found

Items that depend on this one: None found

 

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  • -email is unavailable- added by petrp (Posted a comment)
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    Date Changed by Updated Field Previous Value => Replaced by
    2021-05-01 None Attached File- Added wget-debug.txt, #51350

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