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SubjectPossible race in signal handling
I'm hoping I am wrong, but I think I have found a race in signal 
handling. I believe this can only happen in an SMP system or a system
with preempt on. I'll use 2.6 for the example, but I think it applies
to 2.4, too.

In arch/i386/signal.c, in the do_signal() function, it calls
get_signal_to_deliver() which returns the signal number to deliver
(along with siginfo). get_signal_to_deliver() grabs and releases the
lock, so the signal handler lock is not held in do_signal(). Then the
do_signal() calls handle_signal(), which uses the signal number to
extract the sa_handler, etc.

Since no lock is held, it seems like another thread with the same signal
handler set can come in and call sigaction(), it can change sa_handler
between the call to get_signal_to_deliver() and fetching the value of
sa_handler. If the sigaction() call set it to SIG_IGN, SIG_DFL, or some
other fundamental change, that bad things can happen.

Am I correct here, or am I missing something?

-Corey

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