On Mon, Apr 20, 2020 at 04:29:32PM +0100, Peter Maydell wrote: > On Mon, 20 Apr 2020 at 16:24, Eric Blake <eblake@xxxxxxxxxx> wrote: > > It will be interesting to find how much code (wrongly) assumes it can > > use a blind assignment of fcntl(fd, F_SETFD, 1) and thereby accidentally > > wipes out other existing flags, when it should have instead been doing a > > read-modify-write to protect flags other than FD_CLOEXEC. > > For instance, a quick grep shows 4 instances of this in QEMU :-) Fortunately, most applications aren't going to be interested in forcing 32-bit mode for 64-bit applications, QEMU being the notable exception. We do need to make sure that for 32-bit applications, we either make FD_32BIT_MODE a no-op (don't set the bit, and ignore the bit). We could allow the bit to be visible for 32-bit applications, but we would want to disallow clearing the the bit for 32-bit applications if it was visible. If we did that, then blind assignments of fcntl(fd, F_SETFD, 1) should be mostly harmless with respect to the FD_32BIT_MODE bit. - Ted
