From 27eac47b00789522ba00501b0838026e1ecb6f05 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Mon, 17 Jul 2017 11:35:54 +0200 Subject: net/unix: drop obsolete fd-recursion limits All unix sockets now account inflight FDs to the respective sender. This was introduced in: commit 712f4aad406bb1ed67f3f98d04c044191f0ff593 Author: willy tarreau Date: Sun Jan 10 07:54:56 2016 +0100 unix: properly account for FDs passed over unix sockets and further refined in: commit 415e3d3e90ce9e18727e8843ae343eda5a58fad6 Author: Hannes Frederic Sowa Date: Wed Feb 3 02:11:03 2016 +0100 unix: correctly track in-flight fds in sending process user_struct Hence, regardless of the stacking depth of FDs, the total number of inflight FDs is limited, and accounted. There is no known way for a local user to exceed those limits or exploit the accounting. Furthermore, the GC logic is independent of the recursion/stacking depth as well. It solely depends on the total number of inflight FDs, regardless of their layout. Lastly, the current `recursion_level' suffers a TOCTOU race, since it checks and inherits depths only at queue time. If we consider `A<-B' to mean `queue-B-on-A', the following sequence circumvents the recursion level easily: A<-B B<-C C<-D ... Y<-Z resulting in: A<-B<-C<-...<-Z With all of this in mind, lets drop the recursion limit. It has no additional security value, anymore. On the contrary, it randomly confuses message brokers that try to forward file-descriptors, since any sendmsg(2) call can fail spuriously with ETOOMANYREFS if a client maliciously modifies the FD while inflight. Cc: Alban Crequy Cc: Simon McVittie Signed-off-by: David Herrmann Reviewed-by: Tom Gundersen Signed-off-by: David S. Miller --- include/net/af_unix.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include') diff --git a/include/net/af_unix.h b/include/net/af_unix.h index 678e4d6fa317..3b3194b2fc65 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -58,7 +58,6 @@ struct unix_sock { struct list_head link; atomic_long_t inflight; spinlock_t lock; - unsigned char recursion_level; unsigned long gc_flags; #define UNIX_GC_CANDIDATE 0 #define UNIX_GC_MAYBE_CYCLE 1 -- cgit v1.2.3