expect uses memcpy instead of memmove to copy overlapping memory

[Per Cederqvist]

The ecases_remove_by_expi() function in expect.c uses memcpy() to shift
elements down. The areas can be overlapping. When they are, the
construct is non-portable and can lead to memory corruption.

Please replace the memcpy call with a memmove call. That fixes the
issue. I have attached a proposed patch.

I have already reported this issue at Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=728663

Debian has accepted the patch.

I have also reported it upstream:
https://sourceforge.net/p/expect/patches/16/

The following script demonstrates the problem. Save it in a file called
trigger2.expect and run the following:

$ valgrind expect trigger2.expect

You will see an error message similar to:

==10665== Source and destination overlap in memcpy(0x60b9170, 0x60b9178, 16)
==10665== at 0x4C2E820: memcpy@@GLIBC_2.14 (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)

(Note: it seems that valgrind 3.7 does not detect this, but valgrind 3.8.1 does detect it.)

---cut here for trigger2.expect---
#!/usr/bin/env expect

spawn cat
set a $spawn_id

spawn sleep 1
set b $spawn_id

set spawn_id $a

expect_after {
    -i $a full_buffer { }
    -i $b full_buffer { }
    timeout { }
}

expect eof { }
---cut here for trigger2.expect---

It would be nice if this fix was backported to versions of Ubuntu that are still supported with updates.

[Matthias Klose (doko)]

fixed in 16.04 LTS and later