Once I'd finished upgrading my openssh instances (which are linked against musl not glibc) I thought it'd be interesting to have a poke at musl's syslog(3) and see if it allocates too and so is easily exploitable in the same way. But as far as I can see, it doesn't:

https://github.com/bminor/musl/blob/master/src/misc/syslog.c

Everything there is either on stack or in static variables protected from reentrancy by the lock. The {d,sn,vsn}printf() calls there don't allocate in musl, although they might in glibc. Have I missed anything here?