[Bug stdio/20191] New: libio: vtables hardening

["fweimer at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20191

            Bug ID: 20191
           Summary: libio: vtables hardening
           Product: glibc
           Version: 2.24
            Status: NEW
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---
             Flags: security-

For compatibility with GCC 2.95, libio uses vtables in its implementation. 
While these vtables are in read-only memory, the pointer to them (hidden in
FILE * objects) is not, and attackers can use this to inject completely new
vtables, with function pointers of their own choice.

Some really old binaries (compiled with GCC 2.95 and maybe other pre-3.2 GCC
compilers) may also provide their own vtables, so backwards compatibility in
some form may be necessary.

This is completely new security hardening, so I'm flagging this bug as
security-.

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