Bugs item #1911069, was opened at 2008-03-10 16:31
Message generated for change (Comment added) made by imercury
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Category: libcurl
Group: crash
Status: Open
Resolution: None
Priority: 7
Private: No
Submitted By: Andrey (imercury)
Assigned to: Daniel Stenberg (bagder)
Summary: Race Condition in Curl_resolv(hostip.c) (dns cache)

Initial Comment:
Hello.

I've noticed a bug in Curl_resolv which can lead to crash of curl(or bad behaviour)(I've checked versions 7.16.1 and 7.18.0, but I think older versions are also buggy). Look at hostip.c:423 (curl 7.18.0). Consider we're sharing dns cache between 2 threads(A and B).
A: locks dns cache
A: gets dns from cache
A: unlocks dns cache
B: locks dns cache
B: gets dns from cache
B: unlock dns cache
A: checks remove_entry_if_stale and it returns true
.
So dns entry is removed from cache and thread A knows it, so it sets dns = NULL; but thread B doesn't know it and it has dns variable pointed to nobody knows what...

My solution for that, diff hostip_old.c hostip.c (v7.18.0) is attached. Not sure it's ok, but it worked on 7.16.1 (at least I didn't get curl crashed).

Regards, Andrew..

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>Comment By: Andrey (imercury)
Date: 2008-03-11 14:58

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Not sure it's ok though. It just works in my case..
File Added: mydiff

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Comment By: Daniel Stenberg (bagder)
Date: 2008-03-11 01:33

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Thanks a lot, but can you please make the diff with -u and submit such a
version?

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You can respond by visiting:
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Received on 2008-03-11