Re: [PATCH] libio: Disable vtable validation in case of interposition [BZ #23313]

[Florian Weimer <fweimer at redhat dot com>]

On 06/22/2018 12:51 PM, Florian Weimer wrote:
> Right.  I don't think we need to support static linking for backwards 
> compatibility with these old libraries, so I'll “#ifndef SHARED” around 
> the constructor.

Here's what I've committed.

Thanks,
Florian

Subject: [PATCH COMMITTED] libio: Disable vtable validation in case of interposition [BZ #23313]
To: libc-alpha@sourceware.org

2018-06-26  Florian Weimer  <fweimer@redhat.com>

	[BZ #23313]
	* libio/vtables.c (check_stdfiles_vtables): New ELF constructor.

diff --git a/libio/vtables.c b/libio/vtables.c
index 9fd4ccf642..9df75668c8 100644
--- a/libio/vtables.c
+++ b/libio/vtables.c
@@ -71,3 +71,19 @@ _IO_vtable_check (void)
 
   __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
 }
+
+/* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
+   install their own vtables directly, without calling _IO_init or
+   other functions.  Detect this by looking at the vtables values
+   during startup, and disable vtable validation in this case.  */
+#ifdef SHARED
+__attribute__ ((constructor))
+static void
+check_stdfiles_vtables (void)
+{
+  if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
+      || _IO_2_1_stdout_.vtable != &_IO_file_jumps
+      || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
+    IO_set_accept_foreign_vtables (&_IO_vtable_check);
+}
+#endif