[glibc/release/2.25/master] libio: Disable vtable validation in case of interposition [BZ #23313]

[glibc/release/2.25/master] libio: Disable vtable validation in case of interposition [BZ #23313]

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8440c51d8981e8e40d611a2cbf9850091e7d5a72

commit 8440c51d8981e8e40d611a2cbf9850091e7d5a72
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Jun 26 10:24:52 2018 +0200

    libio: Disable vtable validation in case of interposition [BZ #23313]
    
    (cherry picked from commit c402355dfa7807b8e0adb27c009135a7e2b9f1b0)

Diff:
---
 ChangeLog       |  5 +++++
 libio/vtables.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 9a8840b..94788a9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-26  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #23313]
+	* libio/vtables.c (check_stdfiles_vtables): New ELF constructor.
+
 2019-11-01  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>
 
 	* sysdeps/unix/sysv/linux/mips/Makefile
diff --git a/libio/vtables.c b/libio/vtables.c
index 41b48db..a11226a 100644
--- a/libio/vtables.c
+++ b/libio/vtables.c
@@ -70,3 +70,19 @@ _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