fdcopy(): properly update fd_freefile when skipping non-copyable fdHEADmain

fd_freefile is maintained to fulfill the POSIX guarantee that the lowest
possible file descriptor is allocated on open.  If we skip copying an
fd, it is a possible candidate for the lowest index.

First, the file descriptor installed with a kqueue created
without KQUEUE_CPONFORK missed this handling [*].

Second, fd_freefile should be updated only when the current fd index is
below it.  A skipped fd above fd_freefile could raise it past a free slot.

PR:	300234 [*]
Reported by:	Andrea Venturoli <freebsd@netfence.it>
Reviewed by:	markj
Fixes:	1265516c5c61 ("struct file: add DFLAG_FORK, indicate copying on fork")
Fixes:	809f3121be66 ("fd: assign fd_freefile early when copying")
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D61054

0 files changed, 0 insertions, 0 deletions