On 2022-12-14 15:15, Victoria Dye wrote:
> Matthew John Cheetham via GitGitGadget wrote:
>> +static size_t fwrite_wwwauth(char *ptr, size_t eltsize, size_t nmemb, void *p)
>> +{
>> + size_t size = eltsize * nmemb;
>> + struct strvec *values = &http_auth.wwwauth_headers;
>> + struct strbuf buf = STRBUF_INIT;
>> + const char *val;
>> + const char *z = NULL;
>> +
>> + /*
>> + * Header lines may not come NULL-terminated from libcurl so we must
>> + * limit all scans to the maximum length of the header line, or leverage
>> + * strbufs for all operations.
>> + *
>> + * In addition, it is possible that header values can be split over
>> + * multiple lines as per RFC 2616 (even though this has since been
>> + * deprecated in RFC 7230). A continuation header field value is
>> + * identified as starting with a space or horizontal tab.
>> + *
>> + * The formal definition of a header field as given in RFC 2616 is:
>> + *
>> + * message-header = field-name ":" [ field-value ]
>> + * field-name = token
>> + * field-value = *( field-content | LWS )
>> + * field-content = <the OCTETs making up the field-value
>> + * and consisting of either *TEXT or combinations
>> + * of token, separators, and quoted-string>
>> + */
>> +
>> + strbuf_add(&buf, ptr, size);
>> +
>> + /* Strip the CRLF that should be present at the end of each field */
>> + strbuf_trim_trailing_newline(&buf);
>> +
>> + /* Start of a new WWW-Authenticate header */
>> + if (skip_iprefix(buf.buf, "www-authenticate:", &val)) {
>> + while (isspace(*val))
>> + val++;
>
> Per the RFC [1]:
>
>> The field value MAY be preceded by any amount of LWS, though a single SP
>> is preferred.
>
> And LWS (linear whitespace) is defined as:
>
>> CRLF = CR LF
>> LWS = [CRLF] 1*( SP | HT )
>
> and 'isspace()' includes CR, LF, SP, and HT [2].
>
> Looks good!
>
> [1] https://datatracker.ietf.org/doc/html/rfc2616#section-4-2
> [2] https://linux.die.net/man/3/isspace
>
>> +
>> + strvec_push(values, val);
>
> I had the same question about "what happens with an empty 'val' here?" as
> Stolee did earlier [3], but I *think* the "zero length" (i.e., single null
> terminator) will be copied successfully. It's probably worth testing that
> explicitly, though (I see you set up tests in later patches - ideally a
> "www-authenticate:<mix of whitespace>" line could be tested there).
>
> [3] https://lore.kernel.org/git/9fded44b-c503-f8e5-c6a6-93e882d50e27@xxxxxxxxxx/
There is a bug here. Empty header values would indeed be appended
successfully, but this eventually results in empty values for `wwwauth[]`
being sent over to credential helpers (which should treat the empty value as
a reset of the existing list!!)
Really, empty values should be ignored.
My next iteration should hopefully be a bit more careful around these cases.
>> + http_auth.header_is_last_match = 1;
>> + goto exit;
>> + }
>> +
>> + /*
>> + * This line could be a continuation of the previously matched header
>> + * field. If this is the case then we should append this value to the
>> + * end of the previously consumed value.
>> + */
>> + if (http_auth.header_is_last_match && isspace(*buf.buf)) {
>> + const char **v = values->v + values->nr - 1;
>> + char *append = xstrfmt("%s%.*s", *v, (int)(size - 1), ptr + 1);
>
> In this case (where the line is a continuation of a 'www-authenticate'
> header), it looks like the code here expects *exactly* one LWS at the start
> of the line ('isspace(*buf.buf)' requiring at least one space to append the
> header, 'ptr + 1' skipping no more than one). But, according to the RFC, it
> could be more than one:
>
>> Header fields can be extended over multiple lines by preceding each extra
>> line with at least one SP or HT.
>
> So I think 'buf.buf' might need to have all preceding spaces removed, like
> you did in the "Start of a new WWW-Authenticate header" block.
>
> Also, if you're copying 'ptr' into 'buf' to avoid issues from a missing null
> terminator, wouldn't you want to use 'buf.buf' (instead of 'ptr') in
> 'xstrfmt()'?
Sure! Good points.
>> +
>> + free((void*)*v);
>> + *v = append;
>
> I was about to suggest (optionally) rewriting this to use 'strvec_pop()' and
> 'strvec_push_nodup()':
>
> strvec_pop(values);
> strvec_push_nodup(values, append);
>
> to maybe make this a bit easier to follow, but unfortunately
> 'strvec_push_nodup()' isn't available outside of 'strvec.c'. If you did want
> to use 'strvec' functions, you could remove the 'static' from
> 'strvec_push_nodup()' and add it to 'strvec.h' it in a later reroll, but I
> don't consider that change "blocking" or even important enough to warrant
> its own reroll.
That wouldn't be too much effort, and would help simplify overall the move
to using `strbuf_` functions. Check my next iteration for this.
>> +
>> + goto exit;
>> + }
>> +
>> + /* This is the start of a new header we don't care about */
>> + http_auth.header_is_last_match = 0;
>> +
>> + /*
>> + * If this is a HTTP status line and not a header field, this signals
>> + * a different HTTP response. libcurl writes all the output of all
>> + * response headers of all responses, including redirects.
>> + * We only care about the last HTTP request response's headers so clear
>> + * the existing array.
>> + */
>> + if (skip_iprefix(buf.buf, "http/", &z))
>> + strvec_clear(values);
>
> The comments describing the intended behavior (as well as the commit
> message) are clear and explain the somewhat esoteric (at least to my
> untrained eye ;) ) code. Thanks!
>
>> +
>> +exit:
>> + strbuf_release(&buf);
>> + return size;
>> +}
>> +
>> size_t fwrite_null(char *ptr, size_t eltsize, size_t nmemb, void *strbuf)
>> {
>> return nmemb;
>> @@ -1864,6 +1940,8 @@ static int http_request(const char *url,
>> fwrite_buffer);
>> }
>>
>> + curl_easy_setopt(slot->curl, CURLOPT_HEADERFUNCTION, fwrite_wwwauth);
>> +
>> accept_language = http_get_accept_language_header();
>>
>> if (accept_language)
>
Thanks,
Matthew
