khttpd problems

zuzhihui

khttpd problems
khttpd
, the first http accellerator
built into the Linux kernel, is very fast, especially at serving
small files.  However, it appears to have some stability problems.
It is fairly easy to cause a server running khttpd on some versions of linux
to crash.
As of 2.4.17, it looks like you have to run with only 1 thread, and
avoid quickly cycling it up and down, to have any hope of stability -- and
even then, abruptly terminating client connections causes
an oops fairly frequently.
In 2.4.17, in my initial testing with khttpd, I couldn't fetch .http files
from khttpd because DecodeHeader was getting -EFAULT
back from sock_recvmsg!  Here's the scenario:

khttpd starts.  InitWaitHeaders is called, which allocates Buffer[] in waitheaders.c.

Operator stops khttpd.  StopWaitingForHeaders is called, which frees Buffer[] in waitheaders.c.

Operator restarts khttpd.  *InitWaitHeaders is not called again*.  When WaitForHeaders gets
a header, it calls DecodeHeader, which calls sock_recvmsg with Buffer[] as a buffer, which
causes an EFAULT as the buffer has not been allocated.
This same problem can be triggered by bringing khttpd up and down in a loop.
Here's a
test script
to do that, and
a not-very-enlightening
crash traceback
.
Another minor problem was
found by the Stanford checker
: a value
that cannot be NULL was being checked against NULL.
Patches
Here are patches to fix up khttpd:

• 
  01-khttpd-unbork.patch
  - solves above crash problems
  
• 
  02-khttpd-checker.patch
  - Fix problem found by Stanford Checker
  

I
submitted the first of these to khttpd-users
, but have not asked Marcello to apply the
to the 2.4 kernel.  I probably should.
               
               
               

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