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UPSTREAM: fs, close_range: add flag CLOSE_RANGE_CLOEXEC

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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 <gscrivan@redhat.com>
Link: https://lore.kernel.org/r/20201118104746.873084-2-gscrivan@redhat.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
(cherry picked from commit 582f1fb6b7)
Bug: 216276716
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ib2d44f9760a80e3febdb25925d17ce5ffd14910e
This commit is contained in:
Giuseppe Scrivano
2020-11-18 11:47:45 +01:00
committed by Todd Kjos
parent a185c0f116
commit 737c09e195
2 changed files with 37 additions and 10 deletions
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44
fs/file.c
View File

@@ -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) {
/*

3
include/uapi/linux/close_range.h
View File

@@ -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 */