From 326a490f7f70a7df190560d8e941b60a5e066b59 Mon Sep 17 00:00:00 2001 From: obiwac Date: Wed, 31 Aug 2022 13:03:14 +0200 Subject: [PATCH] src: remap invalid file descriptors using `dup2` When checking for the validity of the stdio file descriptors (nodejs#875), ones which don't exist are intended to be remapped to /dev/null (and, if that doesn't work, we abort). This however doesn't work on all platforms and in all cases, and is not anymore required by POSIX; instead, use the `dup2` syscall as a more robust solution (conforms to POSIX.1). Fixes: https://github.com/nodejs/help/issues/2411 Refs: https://github.com/nodejs/node/pull/875 --- src/node.cc | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/src/node.cc b/src/node.cc index 2891c18bb9aa9a..7379fdab7c1eb0 100644 --- a/src/node.cc +++ b/src/node.cc @@ -608,11 +608,32 @@ static void PlatformInit(ProcessInitializationFlags::Flags flags) { for (auto& s : stdio) { const int fd = &s - stdio; if (fstat(fd, &s.stat) == 0) continue; + // Anything but EBADF means something is seriously wrong. We don't // have to special-case EINTR, fstat() is not interruptible. if (errno != EBADF) ABORT(); - if (fd != open("/dev/null", O_RDWR)) ABORT(); - if (fstat(fd, &s.stat) != 0) ABORT(); + + // If EBADF (file descriptor doesn't exist), open /dev/null and duplicate + // its file descriptor to the invalid file descriptor. Make sure *that* + // file descriptor is valid. POSIX doesn't guarantee the next file + // descriptor open(2) gives us is the lowest available number anymore in + // POSIX.1-2017, which is why dup2(2) is needed. + int null_fd; + + do { + null_fd = open("/dev/null", O_RDWR); + } while (null_fd < 0 && errno == EINTR); + + if (null_fd != fd) { + int err; + + do { + err = dup2(null_fd, fd); + } while (err < 0 && errno == EINTR); + CHECK_EQ(err, 0); + } + + if (fstat(fd, &s.stat) < 0) ABORT(); } }