ahs: jobs: Block signals during tcsetpgrpbusybox

Upstream commit:

    Date: Wed, 6 Jan 2021 15:45:12 +1100
    jobs: Block signals during tcsetpgrp

    Harald van Dijk <harald@gigawatt.nl> wrote:
    > On 19/12/2020 22:21, Steffen Nurpmeso wrote:
    >> Steffen Nurpmeso wrote in
    >>   <20201219172838.1B-WB%steffen@sdaoden.eu>:
    >>   |Long story short, after falsely accusing BSD make of not working
    >>
    >> After dinner i shortened it a bit more, and attach it again, ok?
    >> It is terrible, but now less redundant than before.
    >> Sorry for being so terse, that problem crosses my head for about
    >> a week, and i was totally mislead and if you bang your head
    >> against the wall so many hours bugs or misbehaviours in a handful
    >> of other programs is not the expected outcome.
    >
    > I think a minimal test case is simply
    >
    > all:
    >         $(SHELL) -c 'trap "echo TTOU" TTOU; set -m; echo all good'
    >
    > unless I accidentally oversimplified.
    >
    > The SIGTTOU is caused by setjobctl's xtcsetpgrp(fd, pgrp) call to make
    > its newly started process group the foreground process group when job
    > control is enabled, where xtcsetpgrp is a wrapper for tcsetpgrp. (That's
    > in dash, the other variants may have some small differences.) tcsetpgrp
    > has this little bit in its specification:
    >
    >        Attempts to use tcsetpgrp() from a process which is a member of
    >        a background process group on a fildes associated with its con‐
    >        trolling  terminal  shall  cause the process group to be sent a
    >        SIGTTOU signal. If the calling thread is blocking SIGTTOU  sig‐
    >        nals  or  the  process is ignoring SIGTTOU signals, the process
    >        shall be allowed to perform the operation,  and  no  signal  is
    >        sent.
    >
    > Ordinarily, when job control is enabled, SIGTTOU is ignored. However,
    > when a trap action is specified for SIGTTOU, the signal is not ignored,
    > and there is no blocking in place either, so the tcsetpgrp() call is not
    > allowed.
    >
    > The lowest impact change to make here, the one that otherwise preserves
    > the existing shell behaviour, is to block signals before calling
    > tcsetpgrp and unblocking them afterwards. This ensures SIGTTOU does not
    > get raised here, but also ensures that if SIGTTOU is sent to the shell
    > for another reason, there is no window where it gets silently ignored.
    >
    > Another way to fix this is by not trying to make the shell start a new
    > process group, or at least not make it the foreground process group.
    > Most other shells appear to not try to do this.

    This patch implements the blocking of SIGTTOU (and everything else)
    while we call tcsetpgrp.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

0 files changed, 0 insertions, 0 deletions