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nspawn: lock down a few things in /proc by default
This tightens security on /proc: a couple of files exposed there are now made inaccessible. These files might potentially leak kernel internals or expose non-virtualized concepts, hence lock them down by default. Moreover, a couple of dirs in /proc that expose stuff also exposed in /sys are now marked read-only, similar to how we handle /sys. The list is taken from what docker/runc based container managers generally apply, but slightly extended.
This commit is contained in:
Lennart Poettering
parent
10af01a5ff
commit
d4b653c589
@ -508,6 +508,18 @@ int mount_all(const char *dest,
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uid_t uid_shift, uid_t uid_range,
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const char *selinux_apifs_context) {
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#define PROC_INACCESSIBLE(path) \
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{ NULL, (path), NULL, NULL, MS_BIND, \
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MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO|MOUNT_INACCESSIBLE_REG }, /* Bind mount first ... */ \
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{ NULL, (path), NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT, \
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MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO } /* Then, make it r/o */
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#define PROC_READ_ONLY(path) \
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{ (path), (path), NULL, NULL, MS_BIND, \
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MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* Bind mount first ... */ \
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{ NULL, (path), NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT, \
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MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO } /* Then, make it r/o */
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typedef struct MountPoint {
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const char *what;
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const char *where;
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@ -518,39 +530,72 @@ int mount_all(const char *dest,
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} MountPoint;
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static const MountPoint mount_table[] = {
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/* inner child mounts */
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{ "proc", "/proc", "proc", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV, MOUNT_FATAL|MOUNT_IN_USERNS },
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{ "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND, MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* Bind mount first ... */
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{ "/proc/sys/net", "/proc/sys/net", NULL, NULL, MS_BIND, MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO|MOUNT_APPLY_APIVFS_NETNS }, /* (except for this) */
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{ NULL, "/proc/sys", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT, MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* ... then, make it r/o */
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{ "/proc/sysrq-trigger", "/proc/sysrq-trigger", NULL, NULL, MS_BIND, MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* Bind mount first ... */
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{ NULL, "/proc/sysrq-trigger", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT, MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* ... then, make it r/o */
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/* First we list inner child mounts (i.e. mounts applied *after* entering user namespacing) */
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{ "proc", "/proc", "proc", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
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MOUNT_FATAL|MOUNT_IN_USERNS },
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/* outer child mounts */
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{ "tmpfs", "/tmp", "tmpfs", "mode=1777", MS_NOSUID|MS_NODEV|MS_STRICTATIME, MOUNT_FATAL },
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{ "tmpfs", "/sys", "tmpfs", "mode=755", MS_NOSUID|MS_NOEXEC|MS_NODEV, MOUNT_FATAL|MOUNT_APPLY_APIVFS_NETNS },
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{ "sysfs", "/sys", "sysfs", NULL, MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV, MOUNT_FATAL|MOUNT_APPLY_APIVFS_RO }, /* skipped if above was mounted */
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{ "sysfs", "/sys", "sysfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV, MOUNT_FATAL }, /* skipped if above was mounted */
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{ "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND,
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MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* Bind mount first ... */
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{ "/proc/sys/net", "/proc/sys/net", NULL, NULL, MS_BIND,
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MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO|MOUNT_APPLY_APIVFS_NETNS }, /* (except for this) */
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{ NULL, "/proc/sys", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
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MOUNT_FATAL|MOUNT_IN_USERNS|MOUNT_APPLY_APIVFS_RO }, /* ... then, make it r/o */
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/* Make these files inaccessible to container payloads: they potentially leak information about kernel
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* internals or the host's execution environment to the container */
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PROC_INACCESSIBLE("/proc/kallsyms"),
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PROC_INACCESSIBLE("/proc/kcore"),
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PROC_INACCESSIBLE("/proc/keys"),
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PROC_INACCESSIBLE("/proc/sysrq-trigger"),
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PROC_INACCESSIBLE("/proc/timer_list"),
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/* Make these directories read-only to container payloads: they show hardware information, and in some
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* cases contain tunables the container really shouldn't have access to. */
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PROC_READ_ONLY("/proc/acpi"),
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PROC_READ_ONLY("/proc/apm"),
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PROC_READ_ONLY("/proc/asound"),
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PROC_READ_ONLY("/proc/bus"),
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PROC_READ_ONLY("/proc/fs"),
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PROC_READ_ONLY("/proc/irq"),
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PROC_READ_ONLY("/proc/scsi"),
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/* Then we list outer child mounts (i.e. mounts applied *before* entering user namespacing) */
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{ "tmpfs", "/tmp", "tmpfs", "mode=1777", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
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MOUNT_FATAL },
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{ "tmpfs", "/sys", "tmpfs", "mode=755", MS_NOSUID|MS_NOEXEC|MS_NODEV,
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MOUNT_FATAL|MOUNT_APPLY_APIVFS_NETNS },
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{ "sysfs", "/sys", "sysfs", NULL, MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV,
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MOUNT_FATAL|MOUNT_APPLY_APIVFS_RO }, /* skipped if above was mounted */
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{ "sysfs", "/sys", "sysfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV,
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MOUNT_FATAL }, /* skipped if above was mounted */
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{ "tmpfs", "/dev", "tmpfs", "mode=755", MS_NOSUID|MS_STRICTATIME,
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MOUNT_FATAL },
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{ "tmpfs", "/dev/shm", "tmpfs", "mode=1777", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
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MOUNT_FATAL },
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{ "tmpfs", "/run", "tmpfs", "mode=755", MS_NOSUID|MS_NODEV|MS_STRICTATIME,
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MOUNT_FATAL },
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{ "tmpfs", "/dev", "tmpfs", "mode=755", MS_NOSUID|MS_STRICTATIME, MOUNT_FATAL },
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{ "tmpfs", "/dev/shm", "tmpfs", "mode=1777", MS_NOSUID|MS_NODEV|MS_STRICTATIME, MOUNT_FATAL },
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{ "tmpfs", "/run", "tmpfs", "mode=755", MS_NOSUID|MS_NODEV|MS_STRICTATIME, MOUNT_FATAL },
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#if HAVE_SELINUX
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{ "/sys/fs/selinux", "/sys/fs/selinux", NULL, NULL, MS_BIND, 0 }, /* Bind mount first */
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{ NULL, "/sys/fs/selinux", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT, 0 }, /* Then, make it r/o */
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{ "/sys/fs/selinux", "/sys/fs/selinux", NULL, NULL, MS_BIND,
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0 }, /* Bind mount first */
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{ NULL, "/sys/fs/selinux", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
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0 }, /* Then, make it r/o */
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#endif
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};
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size_t k;
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_cleanup_(unlink_and_freep) char *inaccessible = NULL;
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bool use_userns = (mount_settings & MOUNT_USE_USERNS);
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bool netns = (mount_settings & MOUNT_APPLY_APIVFS_NETNS);
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bool ro = (mount_settings & MOUNT_APPLY_APIVFS_RO);
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bool in_userns = (mount_settings & MOUNT_IN_USERNS);
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size_t k;
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int r;
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for (k = 0; k < ELEMENTSOF(mount_table); k++) {
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_cleanup_free_ char *where = NULL, *options = NULL;
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const char *o;
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const char *o, *what;
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bool fatal = (mount_table[k].mount_settings & MOUNT_FATAL);
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if (in_userns != (bool)(mount_table[k].mount_settings & MOUNT_IN_USERNS))
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@ -566,12 +611,32 @@ int mount_all(const char *dest,
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if (r < 0)
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return log_error_errno(r, "Failed to resolve %s/%s: %m", dest, mount_table[k].where);
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if (mount_table[k].mount_settings & MOUNT_INACCESSIBLE_REG) {
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if (!inaccessible) {
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_cleanup_free_ char *np = NULL;
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r = tempfn_random_child(NULL, "inaccessible", &np);
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if (r < 0)
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return log_error_errno(r, "Failed to generate inaccessible file node path: %m");
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r = touch_file(np, false, USEC_INFINITY, UID_INVALID, GID_INVALID, 0000);
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if (r < 0)
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return log_error_errno(r, "Failed to create inaccessible file node '%s': %m", np);
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inaccessible = TAKE_PTR(np);
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}
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what = inaccessible;
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} else
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what = mount_table[k].what;
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r = path_is_mount_point(where, NULL, 0);
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if (r < 0 && r != -ENOENT)
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return log_error_errno(r, "Failed to detect whether %s is a mount point: %m", where);
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/* Skip this entry if it is not a remount. */
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if (mount_table[k].what && r > 0)
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if (what && r > 0)
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continue;
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r = mkdir_userns_p(dest, where, 0755, mount_settings, uid_shift);
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@ -600,7 +665,7 @@ int mount_all(const char *dest,
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}
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r = mount_verbose(fatal ? LOG_ERR : LOG_DEBUG,
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mount_table[k].what,
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what,
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where,
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mount_table[k].type,
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mount_table[k].flags,
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@ -13,12 +13,13 @@
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#include "volatile-util.h"
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typedef enum MountSettingsMask {
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MOUNT_FATAL = 1 << 0, /* if set, a mount error is considered fatal */
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MOUNT_USE_USERNS = 1 << 1, /* if set, mounts are patched considering uid/gid shifts in a user namespace */
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MOUNT_IN_USERNS = 1 << 2, /* if set, the mount is executed in the inner child, otherwise in the outer child */
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MOUNT_APPLY_APIVFS_RO = 1 << 3, /* if set, /proc/sys, and /sysfs will be mounted read-only, otherwise read-write. */
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MOUNT_APPLY_APIVFS_NETNS = 1 << 4, /* if set, /proc/sys/net will be mounted read-write.
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MOUNT_FATAL = 1U << 0, /* if set, a mount error is considered fatal */
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MOUNT_USE_USERNS = 1U << 1, /* if set, mounts are patched considering uid/gid shifts in a user namespace */
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MOUNT_IN_USERNS = 1U << 2, /* if set, the mount is executed in the inner child, otherwise in the outer child */
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MOUNT_APPLY_APIVFS_RO = 1U << 3, /* if set, /proc/sys, and /sys will be mounted read-only, otherwise read-write. */
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MOUNT_APPLY_APIVFS_NETNS = 1U << 4, /* if set, /proc/sys/net will be mounted read-write.
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Works only if MOUNT_APPLY_APIVFS_RO is also set. */
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MOUNT_INACCESSIBLE_REG = 1U << 5, /* if set, create an inaccessible regular file first and use as bind mount source */
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} MountSettingsMask;
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typedef enum CustomMountType {
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