From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Fw: [Bug 89201] New: sendto changes buffer used by recvfrom of
 other proccesses
Date: Wed, 3 Dec 2014 08:32:41 -0800
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Begin forwarded message:

Date: Wed, 3 Dec 2014 05:51:34 -0800
From: "bugzilla-daemon@bugzilla.kernel.org" <bugzilla-daemon@bugzilla.kernel.org>
To: "stephen@networkplumber.org" <stephen@networkplumber.org>
Subject: [Bug 89201] New: sendto changes buffer used by recvfrom of other proccesses


https://bugzilla.kernel.org/show_bug.cgi?id=89201

            Bug ID: 89201
           Summary: sendto changes buffer used by recvfrom of other
                    proccesses
           Product: Networking
           Version: 2.5
    Kernel Version: 3.4.0-perf-ga6edd5e
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
          Assignee: shemminger@linux-foundation.org
          Reporter: tuxmind.bug@gmail.com
        Regression: No

hi,
i found a bug with recvfrom/sendto.

the affected kernel is the android one, sources can be found there:
https://android.googlesource.com/kernel/msm/+/android-msm-mako-3.4-kitkat-mr2

configuration:
https://android.googlesource.com/kernel/msm/+/android-msm-mako-3.4-kitkat-mr2/arch/arm/configs/mako_defconfig

description:
when a process call recvfrom on a PF_PACKET/SOCK_RAW socket when another
process
call sendto/write on a socket that use the same interface, the ethernet address
is weird.

recvfrom returns the following ethernet header:

UU:XX:00:00:00:00:AA:AA:03:00:00:00:YY:ZZ

instead of

UU:XX:VV:VV:VV:VV:HH:HH:HH:HH:HH:HH:YY:ZZ

where:

  HH:HH:HH:HH:HH:HH is the source MAC address
  UU:XX:VV:VV:VV:VV is the destination MAC address
  YY:ZZ is the ethernet type

i think that recvfrom save the user buffer pointer somewhere because
perform some 'long' work on the buffer ( like using a printf to debug this
problem ) increase the error rate from 2/9480 bad headers to about 779/4301.

i already opened various bug reports and questions.

external references:
 
http://stackoverflow.com/questions/27251904/recvfrom-read-wrong-ethernet-address-from-raw-socket
  https://code.google.com/p/android/issues/detail?id=81370

step to reproduce:

sample program: http://pastebin.com/kkjUrft9
( you have to change the hardcoded ip address )

  > gcc -g -o -DSENDER main.c -o sender
  > gcc -g -o main.c -o receiver
  > ./receiver wlan0 &
  > ./sender wlan0
  > Ctrl+C ( SIGINT ) after a while
  > fg
  > Ctrl+C ( SIGINT )

you should see the amount of sniffed packets and the amount of bad ones.

commenting out the fprintf/fflush calls drastically reduce bad packets count.

thanks in advance for any help.

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