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authorLinus Torvalds <torvalds@linux-foundation.org>2020-08-04 15:12:02 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-04 15:12:02 -0700
commit4f30a60aa78410496e5ffe632a371c00f0d83a8d (patch)
treeb2f74fcd6b286c961f310548de9b2cc855787849 /arch/alpha
parent74858abbb1032222f922487fd1a24513bbed80f9 (diff)
parenta5161eeef97cb0cdc4de966005926db2f5894af4 (diff)
downloadlinux-stericsson-4f30a60aa78410496e5ffe632a371c00f0d83a8d.tar.gz
Merge tag 'close-range-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull close_range() implementation from Christian Brauner: "This adds the close_range() syscall. It allows to efficiently close a range of file descriptors up to all file descriptors of a calling task. This is coordinated with the FreeBSD folks which have copied our version of this syscall and in the meantime have already merged it in April 2019: https://reviews.freebsd.org/D21627 https://svnweb.freebsd.org/base?view=revision&revision=359836 The syscall originally came up in a discussion around the new mount API and making new file descriptor types cloexec by default. During this discussion, Al suggested the close_range() syscall. First, it helps to close all file descriptors of an exec()ing task. This can be done safely via (quoting Al's example from [1] verbatim): /* that exec is sensitive */ unshare(CLONE_FILES); /* we don't want anything past stderr here */ close_range(3, ~0U); execve(....); The code snippet above is one way of working around the problem that file descriptors are not cloexec by default. This is aggravated by the fact that we can't just switch them over without massively regressing userspace. For a whole class of programs having an in-kernel method of closing all file descriptors is very helpful (e.g. demons, service managers, programming language standard libraries, container managers etc.). Second, it allows userspace to avoid implementing closing all file descriptors by parsing through /proc/<pid>/fd/* and calling close() on each file descriptor and other hacks. From looking at various large(ish) userspace code bases this or similar patterns are very common in service managers, container runtimes, and programming language runtimes/standard libraries such as Python or Rust. In addition, the syscall will also work for tasks that do not have procfs mounted and on kernels that do not have procfs support compiled in. In such situations the only way to make sure that all file descriptors are closed is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery. Based on Linus' suggestion close_range() also comes with a new flag CLOSE_RANGE_UNSHARE to more elegantly handle file descriptor dropping right before exec. This would usually be expressed in the sequence: unshare(CLONE_FILES); close_range(3, ~0U); as pointed out by Linus it might be desirable to have this be a part of close_range() itself under a new flag CLOSE_RANGE_UNSHARE which gets especially handy when we're closing all file descriptors above a certain threshold. Test-suite as always included" * tag 'close-range-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: tests: add CLOSE_RANGE_UNSHARE tests close_range: add CLOSE_RANGE_UNSHARE tests: add close_range() tests arch: wire-up close_range() open: add close_range()
Diffstat (limited to 'arch/alpha')
-rw-r--r--arch/alpha/kernel/syscalls/syscall.tbl1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 5ddd128d4b7a..a28fb211881d 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -475,6 +475,7 @@
543 common fspick sys_fspick
544 common pidfd_open sys_pidfd_open
# 545 reserved for clone3
+546 common close_range sys_close_range
547 common openat2 sys_openat2
548 common pidfd_getfd sys_pidfd_getfd
549 common faccessat2 sys_faccessat2