From dffd011480d727a819c537edf3b90ef063731725 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Thu, 21 Nov 2019 12:59:28 -0800
Subject: [PATCH] docs, parallelism: Do not leak blocking mode to other readers
Setting non-blocking via a local copy of the jobserver file descriptor
is safer than just assuming other reader processes with the same fd open
are prepared for it to be non-blocking.
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/lkml/44c01043-ab24-b4de-6544-e8efd153e27a@rasmusvillemoes.dk
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20191121205929.40371-3-keescook@chromium.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
---
scripts/jobserver-count | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/scripts/jobserver-count b/scripts/jobserver-count
index 6e15b38df3d08..7807bfa7dafa7 100755
--- a/scripts/jobserver-count
+++ b/scripts/jobserver-count
@@ -12,12 +12,6 @@ default="1"
if len(sys.argv) > 1:
default=sys.argv[1]
-# Set non-blocking for a given file descriptor.
-def nonblock(fd):
- flags = fcntl.fcntl(fd, fcntl.F_GETFL)
- fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
- return fd
-
# Extract and prepare jobserver file descriptors from envirnoment.
try:
# Fetch the make environment options.
@@ -31,8 +25,12 @@ try:
# Parse out R,W file descriptor numbers and set them nonblocking.
fds = opts[0].split("=", 1)[1]
reader, writer = [int(x) for x in fds.split(",", 1)]
- reader = nonblock(reader)
-except (KeyError, IndexError, ValueError, IOError):
+ # Open a private copy of reader to avoid setting nonblocking
+ # on an unexpecting process with the same reader fd.
+ reader = os.open("/proc/self/fd/%d" % (reader),
+ os.O_RDONLY | os.O_NONBLOCK)
+except (KeyError, IndexError, ValueError, IOError, OSError) as e:
+ print(e, file=sys.stderr)
# Any missing environment strings or bad fds should result in just
# using the default specified parallelism.
print(default)
--
GitLab