[PATCH 1/7] man/man7/unix.7: ERRORS: ETOOMANYREFS: Fix the conditions

["Günther Noack" <gnoack3000@gmail.com>]

The ETOOMANYREFS error is detected in too_many_unix_fds() in
net/unix/af_unix.c when the user's (not the processes') in-flight FDs
exceed RLIMIT_NOFILE, and the process has neither CAP_SYS_RESOURCE nor
CAP_SYS_ADMIN.  The error is raised when all of the following
(simplified) conditions are true:

* user->unix_inflight > task_rlimit(p, RLIMIT_NOFILE)
* !capable(CAP_SYS_RESOURCE)
* !capable(CAP_SYS_ADMIN)

The check was introduced in linux.git 712f4aad406b (2016-01-11; "unix:
properly account for FDs passed over unix sockets").

Fixes: dc4eea68b565 (2016-12-17; "unix.7: Document ETOOMANYREFS for SCM_RIGHTS send exceeding RLIMIT_NOFILE limit")
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Assisted-by: LLM
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
---

Notes:
    Double checked in code -- the condition under which this error is
    returned was not fully spelled out.

 man/man7/unix.7 | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/man/man7/unix.7 b/man/man7/unix.7
index 79198445c581..0d2ea8bda2ae 100644
--- a/man/man7/unix.7
+++ b/man/man7/unix.7
@@ -785,10 +785,14 @@ when sending a file descriptor as ancillary data over
 a UNIX domain socket (see the description of
 .BR SCM_RIGHTS ,
 above).
-It occurs if the number of "in-flight" file descriptors exceeds the
+It occurs if the number of "in-flight" file descriptors
+sent by processes of the caller's real user ID
+exceeds the caller's
 .B RLIMIT_NOFILE
-resource limit and the caller does not have the
+resource limit and the caller has neither the
 .B CAP_SYS_RESOURCE
+nor the
+.B CAP_SYS_ADMIN
 capability.
 An in-flight file descriptor is one that has been sent using
 .BR sendmsg (2)
-- 
2.56.0