At init, and then whenever the TERM variable changes, ed_setup()
uses sh_trap() to run the external 'tput' command to get the
current terminal escape sequence for moving up the cursor one line.
A sh_trap() call executes a shell command as if a shell script's
trap action had executed it, so is subject to modes like the
restricted mode. As of 7ff6b73b, we execute tput using its absolute
path (found and hardcoded at compile time) for better
robustness/security. This fails in restricted mode as it does not
allow executing commands by absolute path. But in C, nothing stops
us from turning that off.
src/cmd/ksh93/edit/edit.c: ed_setup():
- Block SIGINT while doing all of the following, so the user can't
interrupt it and escape from restricted mode. Even without that,
it's probably a good idea to do this, so an interrupt doesn't
cause an inconsistent state.
Note that sigblock() and sigrelease() are macros defined in
features/sigfeatures. To get those, we need to include <fault.h>.
- Temporarily turn off SH_RESTRICTED before sh_trap()ping tput to
get the terminal command to move the cursor up one position.
- Avoid potentially using a sequence that was cut off. Only use the
resulting string if its length does not exceed the space reserved
for CURSOR_UP. Otherwise, empty it.
src/cmd/ksh93/Mamfile:
- Add fault.h dependency to edit.c.
src/cmd/ksh93/edit/history.c:
- Fix typos in introductory comment.
ef8b80cfd7