Hi folks, Bug #422909 has resulted from a broken assumption in how the shell would handle errors, and I'm unsure exactly how to do this correctly. Any assistance would be greatly appreciated. Given that this can in some circumstances result in severe dataloss, I'd very much like to get this right.
The actual problematic code is here: http://svn.debian.org/wsvn/buildd-tools/trunk/schroot/bin/schroot/setup/10mount?op=file&rev=0&sc=0 : # Unmount all filesystem under specified location # $1: mount base location do_umount_all() { "$LIBEXEC_DIR/schroot-listmounts" -m "$1" | while read mountloc; do if [ "$AUTH_VERBOSITY" = "verbose" ]; then echo "Unmounting $mountloc" fi umount "$mountloc" || exit 1 done || exit 1 } The problem here is that if schroot-listmounts segfaults (the trigger in this case) or returns an error, the script continues without any indication of the fact, despite "set -e" being in effect. In this bug this results in a failure to umount a set of mounted filesystems, and then an "rm -rf" taking out all the data further down the line. A small testcase to demonstrate:
int
main (void)
{
char *s = "segfault me";
*s = 'p';
return 0;
}
#!/bin/sh
set -e
# This SEGV goes unnoticed.
./segfault |
while read line; do
echo "Line: $line"
done || exit 3
# This one is noticed.
./segfault
trueHow can I rewrite the while loop securely (and preferably avoiding tmpfiles), such that any bad exit status or failure will result in immediate termination of the script with an error status? Sorry if this is too basic for -devel, but I need to be sure it's correct. Many thanks, Roger -- .''`. Roger Leigh : :' : Debian GNU/Linux http://people.debian.org/~rleigh/ `. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/ `- GPG Public Key: 0x25BFB848 Please GPG sign your mail.
pgpCcoBklvLAP.pgp
Description: PGP signature
