From 737c09e19577c96b23beb28c04a0abdfcf4701cc Mon Sep 17 00:00:00 2001 From: Giuseppe Scrivano Date: Wed, 18 Nov 2020 11:47:45 +0100 Subject: [PATCH] UPSTREAM: fs, close_range: add flag CLOSE_RANGE_CLOEXEC MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When the flag CLOSE_RANGE_CLOEXEC is set, close_range doesn't immediately close the files but it sets the close-on-exec bit. It is useful for e.g. container runtimes that usually install a seccomp profile "as late as possible" before execv'ing the container process itself. The container runtime could either do: 1 2 - install_seccomp_profile(); - close_range(MIN_FD, MAX_INT, 0); - close_range(MIN_FD, MAX_INT, 0); - install_seccomp_profile(); - execve(...); - execve(...); Both alternative have some disadvantages. In the first variant the seccomp_profile cannot block the close_range syscall, as well as opendir/read/close/... for the fallback on older kernels. In the second variant, close_range() can be used only on the fds that are not going to be needed by the runtime anymore, and it must be potentially called multiple times to account for the different ranges that must be closed. Using close_range(..., ..., CLOSE_RANGE_CLOEXEC) solves these issues. The runtime is able to use the existing open fds, the seccomp profile can block close_range() and the syscalls used for its fallback. Signed-off-by: Giuseppe Scrivano Link: https://lore.kernel.org/r/20201118104746.873084-2-gscrivan@redhat.com Signed-off-by: Christian Brauner (cherry picked from commit 582f1fb6b721facf04848d2ca57f34468da1813e) Bug: 216276716 Signed-off-by: Maciej Żenczykowski Change-Id: Ib2d44f9760a80e3febdb25925d17ce5ffd14910e --- fs/file.c | 44 ++++++++++++++++++++++++-------- include/uapi/linux/close_range.h | 3 +++ 2 files changed, 37 insertions(+), 10 deletions(-) diff --git a/fs/file.c b/fs/file.c index 9d02352fa18c..421daa4e4e4f 100644 --- a/fs/file.c +++ b/fs/file.c @@ -672,6 +672,35 @@ int __close_fd(struct files_struct *files, unsigned fd) } EXPORT_SYMBOL(__close_fd); /* for ksys_close() */ +static inline void __range_cloexec(struct files_struct *cur_fds, + unsigned int fd, unsigned int max_fd) +{ + struct fdtable *fdt; + + if (fd > max_fd) + return; + + spin_lock(&cur_fds->file_lock); + fdt = files_fdtable(cur_fds); + bitmap_set(fdt->close_on_exec, fd, max_fd - fd + 1); + spin_unlock(&cur_fds->file_lock); +} + +static inline void __range_close(struct files_struct *cur_fds, unsigned int fd, + unsigned int max_fd) +{ + while (fd <= max_fd) { + struct file *file; + + file = pick_file(cur_fds, fd++); + if (!file) + continue; + + filp_close(file, cur_fds); + cond_resched(); + } +} + /** * __close_range() - Close all file descriptors in a given range. * @@ -687,7 +716,7 @@ int __close_range(unsigned fd, unsigned max_fd, unsigned int flags) struct task_struct *me = current; struct files_struct *cur_fds = me->files, *fds = NULL; - if (flags & ~CLOSE_RANGE_UNSHARE) + if (flags & ~(CLOSE_RANGE_UNSHARE | CLOSE_RANGE_CLOEXEC)) return -EINVAL; if (fd > max_fd) @@ -725,16 +754,11 @@ int __close_range(unsigned fd, unsigned max_fd, unsigned int flags) } max_fd = min(max_fd, cur_max); - while (fd <= max_fd) { - struct file *file; - file = pick_file(cur_fds, fd++); - if (!file) - continue; - - filp_close(file, cur_fds); - cond_resched(); - } + if (flags & CLOSE_RANGE_CLOEXEC) + __range_cloexec(cur_fds, fd, max_fd); + else + __range_close(cur_fds, fd, max_fd); if (fds) { /* diff --git a/include/uapi/linux/close_range.h b/include/uapi/linux/close_range.h index 6928a9fdee3c..2d804281554c 100644 --- a/include/uapi/linux/close_range.h +++ b/include/uapi/linux/close_range.h @@ -5,5 +5,8 @@ /* Unshare the file descriptor table before closing file descriptors. */ #define CLOSE_RANGE_UNSHARE (1U << 1) +/* Set the FD_CLOEXEC bit instead of closing the file descriptor. */ +#define CLOSE_RANGE_CLOEXEC (1U << 2) + #endif /* _UAPI_LINUX_CLOSE_RANGE_H */