Calling printf with %f format from rtld-audit bound functions results in a segfault.

[Marcus Borkenhagen]

Calling printf functions from an rtld-audit wrapped function - not even the wrapper itself - results in a segfault from apparently ld-linux.so.

[A complete example will be attached to this bugreport.]

When the following function is called via a rtld-audit rebound wrapper, a segfault will occur on the last printf-call (the one with the %f format.) This segfault apparently happens on return from the dynamic linker itself, which seems to break its stack.

 ,-----
 | int fourtytwo(void) {
 | printf("42.%s\n", __func__);
 | printf("42.%s The current float is %a\n", __func__, 42.1618);
 | printf("42.%s The current float is %f\n", __func__, 42.1618);
 | return 42;
 | }
 `-----

Ubuntu Version:
Description: Ubuntu 19.10
Release: 19.10

Package Version:
libc6:
  Installed: 2.30-0ubuntu2.1
  Candidate: 2.30-0ubuntu2.1
  Version table:
 *** 2.30-0ubuntu2.1 500
        500 http://de.archive.ubuntu.com/ubuntu eoan-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2.30-0ubuntu2 500
        500 http://de.archive.ubuntu.com/ubuntu eoan/main amd64 Packages

[Marcus Borkenhagen (mborkenhagen-aox-tech)]

Further testing showed that the attached rtld-audit-repro.tar.xz did not reproduce the described behavior.

An updated and much simpler repro in audit.c wich does actually reproduce the described issue.

[Marcus Borkenhagen (mborkenhagen-aox-tech)]

New repro that actually works.