Commit 22376023 authored by Alexander Richardson's avatar Alexander Richardson
Browse files

dix/privates.c: Avoid undefined behaviour after realloc()



Adding the offset between the realloc result and the old allocation to
update pointers into the new allocation is undefined behaviour: the
old pointers are no longer valid after realloc() according to the C
standard. While this works on almost all architectures and compilers,
it causes  problems on architectures that track pointer bounds (e.g.
CHERI or Arm's Morello): the DevPrivateKey pointers will still have the
bounds of the previous allocation and therefore any dereference will
result in a run-time trap.

I found this due to a crash (dereferencing an invalid capability) while
trying to run `XVnc` on a CHERI-RISC-V system. With this commit I can
successfully connect to the XVnc instance running inside a QEMU with a
VNC viewer on my host.
Signed-off-by: Alexander Richardson's avatarAlex Richardson <Alexander.Richardson@cl.cam.ac.uk>
parent f6f2f203
Pipeline #365735 passed with stages
in 4 minutes and 29 seconds