Red Hat Bugzilla – Bug 69254
long regexp match causes perl coredump
Last modified: 2007-11-30 17:10:30 EST
With perl-5.8.0-42, this perl script coredumps:
$lines = 906;
$_ = "foo\n" x $lines . "\n\n*** EOOH ***\n" . "foo\n" x $lines;
/^((?:.+\n)*)\n*\*\*\* EOOH \*\*\*\n((?:.+\n)*)\n+/;
If this is related to a stack overflow or something like that, you may have to
increase the setting of $lines on your system to see the coredump.
Decreasing $lines makes the coredump go away, thus confirming that this is some
sort of memory overrun.
I can't reproduce this with perl-5.8.0-48, even with $lines = 65536. can you
confirm whether it still exists or not?
It still happens for me with perl-5.8.0-49.
I can't reproduce this problem either (with perl-5.8.0-50). What locale are
you using, and what does the stack trace look like when it crashes?
It's still happening for me with -50. I have LC_COLLATE set to C and LANG set
to en_US. No other locale environment variables are set. It looks like the
stack is trashed in the core dump:
#0 0x400e6508 in S_regmatch ()
Cannot access memory at address 0xbfe00fd0
See also http://bugs.debian.org/cgi-bin/bugreport.cgi?archive=no\&bug=158300
which appears related.
There are some additional test cases in that bug which might help.
the latest rawhide perl, perl-5.8.0-70, passes all of the test cases above as
well as those in debian bugzilla
I'm still seeing the segfault running the above code with perl-5.8.0-83.
Attaching strace output.
Created attachment 89378 [details]
perl strace output
Updating from glibc-2.3.1-46 to glibc-2.3.1-51 fixed the segfault for me.
Umm, actually appears to be related to NPTL vs. Linuxthreads - the glibc upgrade
turned NPTL back on, and once I turned NPTL off, the segfault came back.
Since NPTL is the default, this is low priority.
Closing out some bugs that have been in MODIFIED state. Please reopen if they
This bug persists for me with perl-5.8.1-90.rc2.1, glibc-2.3.2-57, and a
non-NPTL kernel, but only if I increase $lines in the test script to 3447. With
$lines set to 3446, Perl doesn't segfault.
Reproducible on a 256 MB machine, Fedora Core 1, perl-5.8.3-16, $lines
Not attaching core dump (> 10 MB) ;)
This bug can be reproduced with $lines = 4366 on perl v5.8.5 built for
i386-linux-thread-multi running under Mandrake 10.1 (Linux version 22.214.171.124-10mdk)
Closing because reports are from old Fedora, and a Mandrake report is
meaningless. Open a NEW report if this is still an issue with a supported Fedora
Well, this coredumps for me on FC-4.
With lines set to 3929 it crashes, and with lines set to 3928 it doesn't. I'm
not sure whether or not this actually represents a problem. After all, I can
make practically anything coredump by allocating too much memory or whatever and
it doesn't represent a security problem. Changing my stacksize ulimit will
change the number of lines at which the problem happens.
Here is my system data.
$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
file size (blocks, -f) unlimited
pending signals (-i) 16383
max locked memory (kbytes, -l) 32
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 16383
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
$ rpm -q perl
$ uname -rvm
2.6.12-1.1447_FC4smp #1 SMP Fri Aug 26 21:03:12 EDT 2005 x86_64
$ cat /etc/redhat-release
Fedora Core release 4 (Stentz)
"After all, I can make practically anything coredump by allocating too much
memory or whatever" -- I disagree completely. A program is not supposed to
coredump if you ask it to do something which takes too much memory. It's
supposed to tell you that it couldn't do it. Any program which coredumps is by
It would be helpful if someone could install the debuginfo package and get a gdb
backtrace to attach here, along with the perl code used to reproduce that backtrace.
I am confused. Why do you need us to provide a gdb backtrace when I've already
provided (over three years ago) a 3-line perl script with which you can
trivially duplicate the problem? Wouldn't it be more useful for debugging for
you to reproduce the problem yourself in a running perl instance inside gdb
rather than having someone provide a static gdb backtrace which it seems that
you could just as easily produce yourself?
Not to mention that the backtrace is over 15000 frames long.
Good point, a stack trace isn't useful.
I talked with a perl expert, and he said that you can only trigger this behavior
with poor regexp coding. Nesting expressions in this way is inherently
exponential in complexity which is discussed in man perlretut.
What do you expect to happen when the stack grows to an unmanagable size due to
a problematic regexp? Perhaps perl could be improved to fail with an error
message, but that wouldn't be any different from perl stopping in this
situation. perl is doing exactly as it is designed to do, and the stack is of
This is not a Fedora specific problem, so you should file this upstream.
However I don't think upstream can really do anything about this.
Python had a similar sort of problem with isinstance. I found it, and I made
the same argument as email@example.com. The Python people agreed with
me, and in thinking about it carefully, they were right to. Language
interpreters especially should not just core dump because of a stack overflow.
But upstream at the perl maintainers is the right place to deal with it.
Since I don't actually use perl if I can help it, I'll leave it to someone else.
I just tested because I'm watching all the 'make Cambridge better' dependencies
and I didn't like the reason it was being closed. :-)