[lwip-devel] [bug #49863] Data race in netconn_gethostbyname()

[Thomas Mueller]

URL:
  <http://savannah.nongnu.org/bugs/?49863>

                 Summary: Data race in netconn_gethostbyname()
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: tmu
            Submitted on: Fri 16 Dec 2016 01:35:03 PM GMT
                Category: DNS
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.0.0

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Details:

Function netconn_gethostbyname() uses tcpip_callback() to
execute lwip_netconn_do_gethostbyname() in the context
of tcpip_thread. In configurations with LWIP_MPU_COMPATIBLE=0
netconn_gethostbyname() passes the address of local variable
'err' in the argument to function lwip_netconn_do_gethostbyname()
Variable 'err' is also used to store the return value of tcpip_callback().

Depending on scheduling policies and priorities, the function
to be executed by the tcpip_thread may have completed before
function tcpip_callback() returns and storing the return value
of tcpip_callback() in 'err' will overwrite the value returned
by lwip_netconn_do_gethostbyname().

Using a separate local variable to store the return value of
tcpip_callback() resolves the issue.








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