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Fix some UB in signal handling #18

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Fix some UB in signal handling #18

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Commits on Aug 25, 2019

  1. microcom: initialize the struct sigaction before use 

    sigaction(2) reads the sa_mask and sa_flags struct members as well, but
we didn't initialize them so far. We probably didn't run into problems,
because we allocate it when the stack is fresh and full of zeroes.

Fix this by explicitly zeroing the struct and emptying the signal set.

Signed-off-by: Ahmad Fatoum <[email protected]>
    @a3f
    a3f committed Aug 25, 2019
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  2. Don't call async-signal-unsafe free in signal handler 

    We use malloc elsewhere in the code with signals unmasked, but use free
in a signal handler. This could result in a dead lock when terminating
microcom by signal.

The duplication of exit(0) call is ok, as the call site in the signal
handler will be replaced in a follow-up commit.

Signed-off-by: Ahmad Fatoum <[email protected]>
    @a3f
    a3f committed Aug 25, 2019
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  3. microcom: make microcom_exit async-signal-safer 

    Both printf and exit aren't async signal safe, replace them with write
and _Exit respectively.

The access to ios and ios->exit and callees is still illegal, but at
least we don't run risk reentering stdio and causing a deadlock anymore.

As exit flushes stdio buffers as well, we now risk losing unflushed
stdio output. This is acceptable as we aren't buffering the serial
port output and the program is being terminated abnormally anyway.

Signed-off-by: Ahmad Fatoum <[email protected]>
    @a3f
    a3f committed Aug 25, 2019
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