net: unix: fix inflight counting bug in garbage collector
Previously I assumed that the receive queues of candidates don't
change during the GC. This is only half true, nothing can be received
from the queues (see comment in unix_gc()), but buffers could be added
through the other half of the socket pair, which may still have file
descriptors referring to it.
This can result in inc_inflight_move_tail() erronously increasing the
"inflight" counter for a unix socket for which dec_inflight() wasn't
previously called. This in turn can trigger the "BUG_ON(total_refs <
inflight_refs)" in a later garbage collection run.
Fix this by only manipulating the "inflight" counter for sockets which
are candidates themselves. Duplicating the file references in
unix_attach_fds() is also needed to prevent a socket becoming a
candidate for GC while the skb that contains it is not yet queued.
[Ported git-6209344 by Konstantin]
Reported-by: Andrea Bittau <firstname.lastname@example.org>
Signed-off-by: Miklos Szeredi <email@example.com>
Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
Signed-off-by: Konstantin Khorenko <email@example.com>
Signed-off-by: Pavel Emelyanov <firstname.lastname@example.org>