1233813 - [MDNS] fix issue with resolving services with no TXT records

Status: RESOLVED FIXED

(Core :: Networking, defect)

Description

[Kannan Vijayan [:djvj]]

Attachment: fix-mdns-attributes-set.patch

Resolving mDNS services with zero TXT records causes a crash, for the following reasons:

In MDNSResponderOperator.cpp, we initialize the "attributes" property bag to nullptr if there are no TXT attributes.
  See: https://dxr.mozilla.org/mozilla-central/source/netwerk/dns/mdns/libmdns/MDNSResponderOperator.cpp#635

Later, in GetAddrInfoOperator::Reply, we construct a new instance of nsDNSServiceInfo using the previous instance (which has a null |attributes| field).
  See: https://dxr.mozilla.org/mozilla-central/source/netwerk/dns/mdns/libmdns/MDNSResponderOperator.cpp#757

This crashes in nsDNSServiceInfo's initialize-from-pointer constructor.
  See: https://dxr.mozilla.org/mozilla-central/source/netwerk/dns/mdns/libmdns/nsDNSServiceInfo.cpp#46


The issue is that when |nsDNSServiceInfo->SetAttribute()| gets called with a nullptr, its |mIsAttributesSet| is set to true unconditionally.  That should depend on whether the incoming pointer is null or not.

Fix attached.

Comment 1

[Shih-Chiang Chien [:schien] (UTC+8) (use ni? plz)]

Comment on attachment 8700130 [details] [diff] [review]
fix-mdns-attributes-set.patch

Review of attachment 8700130 [details] [diff] [review]:
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Thanks for catching this bug!

Comment 2

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/d57e201a2d38

Comment 3

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/d57e201a2d38