system/ruby: libedit compatibility patch [read:]

Ruby pretends editline (libedit) is readline.  This is normally fine.
However, editline's readline emulation does not account for changes to
rl_instream or rl_outstream.  If a Ruby application using the Readline
extension changes .input or .output, this will cause a use-after-free:

==32694== Invalid read of size 4
==32694==    at 0x4070A38: fwrite (fwrite.c:32)
==32694==    by 0x406F707: fputs (fputs.c:7)
==32694==    by 0x660EAC7: el_wgets (in /usr/lib/libedit.so.0.0.60)
==32694==    by 0x6607BDB: el_gets (in /usr/lib/libedit.so.0.0.60)
==32694==    by 0x6620EDB: readline (in /usr/lib/libedit.so.0.0.60)
==32694==    by 0x65DE3D3: readline_get (readline.c:346)
==32694==    by 0x4DFA49B: rb_protect (eval.c:996)
==32694==    by 0x65DE4FF: readline_readline (readline.c:507)
==32694==    by 0x4F7AD4B: call_cfunc_m1 (vm_insnhelper.c:1723)
==32694==  Address 0x67503dc is 140 bytes inside a block of size 1,264 free'd
==32694==    at 0x490AFC0: free (in /usr/lib/valgrind/vgpreload_memcheck-ppc64be-linux.so)
==32694==    by 0x406D44F: fclose (fclose.c:35)
==32694==    by 0x65DE013: clear_rl_outstream (readline.c:365)
==32694==    by 0x65DE0DF: readline_s_set_output (readline.c:599)
==32694==  Block was alloc'd at
==32694==    at 0x49092C0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-ppc64be-linux.so)
==32694==    by 0x406BEC7: fdopen (__fdopen.c:21)
==32694==    by 0x65DE103: readline_s_set_output (readline.c:603)

Since rl_instream and rl_outstream are read on each rl_initialize, and
editline's rl_initialize is smart enough to not leak memory if it is
called multiple times during program execution, we use this as a way to
force re-reading of rl_instream and rl_outstream.

I hate this patch; I really do.  Better fixes are highly welcome.

1 files changed, 22 insertions, 0 deletions

diff --git a/system/ruby/libedit-compat.patch b/system/ruby/libedit-compat.patch
new file mode 100644
index 000000000..601a9feea
--- /dev/null
+++ b/system/ruby/libedit-compat.patch
@@ -0,0 +1,22 @@
+--- ruby-2.5.5/ext/readline/readline.c.old	2017-09-30 08:35:23.000000000 +0000
++++ ruby-2.5.5/ext/readline/readline.c	2019-09-09 06:12:00.300098741 +0000
+@@ -571,6 +571,9 @@
+             rb_syserr_fail(save_errno, "fdopen");
+         }
+         rl_instream = readline_rl_instream = f;
++#ifdef HAVE_EDITLINE_READLINE_H
++        rl_initialize();
++#endif
+         readline_instream = input;
+     }
+     return input;
+@@ -607,6 +610,9 @@
+             rb_syserr_fail(save_errno, "fdopen");
+         }
+         rl_outstream = readline_rl_outstream = f;
++#ifdef HAVE_EDITLINE_READLINE_H
++        rl_initialize();
++#endif
+         readline_outstream = output;
+     }
+     return output;