On Sat, 2010-09-25 at 23:30 +0200, Guilhem Bonnefille wrote:
> Hi,
>
> I'm testing ETag branch.
>
> I encountered some segfault. The segfault occurs in a
> curl_check_header function, called by curl_easy_perform. With gdb I
> found that the error is certainly due to memory corruption. So I ran
> viking under valgrind. The latter reports that the matter is a read
> from a freed memory.
>
> But the most surprising is that the free occurs AFTER the context of the
> error:
> - free at curl_download.c:216
> - curl_easy_perform at curl_download.c:189
> (line numbers can be incorrect as I played with code to understand).
>
> So, I naturally think about multi-thread issue. But I do not
> understand what can go wrong.
>
> Any tip welcome.
What I think happens is:
1) We first do a request for a tile with an ETag and apply a custom
header, this gets set into the conn->data->set.headers pointer
2) The header gets freed, but the set.headers pointer is left as a
dangling reference to the memory
3) A subsequent request is generated for a tile without an etag so we do
not overwrite the set.headers pointer and it keeps the old, invalid
value and the HTTP request code tries to reference it.
I believe the following change should fix it by ensuring the dangling
pointer gets cleared during step (2).
diff --git a/src/curl_download.c b/src/curl_download.c
index 0eb2b45..2e7a7ef 100644
--- a/src/curl_download.c
+++ b/src/curl_download.c
@@ -213,8 +213,10 @@ int curl_download_uri ( const char *uri, FILE *f,
DownloadMapOptions *options, D
}
if (!handle)
curl_easy_cleanup ( curl );
- if (curl_send_headers)
+ if (curl_send_headers) {
curl_slist_free_all(curl_send_headers);
+ curl_easy_setopt ( curl, CURLOPT_HTTPHEADER , NULL);
+ }
return res;
}
Jon
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