[Bug stdio/30039] __vsprintf_internal does not handle unspecified buffer length in fortify mode

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

https://sourceware.org/bugzilla/show_bug.cgi?id=30039

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
              Flags|                            |security-
   Target Milestone|---                         |2.37

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
Fixed for 2.37 via:

commit 0d50f477f47ba637b54fb03ac48d769ec4543e8d
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed Jan 25 08:01:00 2023 +0100

    stdio-common: Handle -1 buffer size in __sprintf_chk & co (bug 30039)

    This shows up as an assertion failure when sprintf is called with
    a specifier like "%.8g" and libquadmath is linked in:

    Fatal glibc error: printf_buffer_as_file.c:31
      (__printf_buffer_as_file_commit): assertion failed:
      file->stream._IO_write_ptr <= file->next->write_end

    Fix this by detecting pointer wraparound in __vsprintf_internal
    and saturate the addition to the end of the address space instead.

    Reviewed-by: Carlos O'Donell <carlos@redhat.com>
    Tested-by: Carlos O'Donell <carlos@redhat.com>

Introduce in the vfprintf refactoring, so need for backporting.

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