Setting non-blocking via a local copy of the jobserver file descriptor is safer than just assuming the writer on the original fd is prepared for it to be non-blocking. Suggested-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/lkml/44c01043-ab24-b4de-6544-e8efd153e27a@xxxxxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- scripts/jobserver-count | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/scripts/jobserver-count b/scripts/jobserver-count index 6e15b38df3d0..a68a04ad304f 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 +25,13 @@ 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 writer. + reader = os.open("/proc/self/fd/%d" % (reader), os.O_RDONLY) + flags = fcntl.fcntl(reader, fcntl.F_GETFL) + fcntl.fcntl(reader, fcntl.F_SETFL, flags | 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) -- 2.17.1
