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Merge pull request #14532 from poettering/namespace-dynamic-user-fix

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Make DynamicUser=1 work in a userns container
This commit is contained in:
Lennart Poettering 2020-01-13 16:47:15 +01:00 committed by GitHub
commit 575a915a74
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3 changed files with 92 additions and 41 deletions
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10
src/core/namespace.c
View File

@ -1063,14 +1063,6 @@ static int apply_mount(
return 0;
}
/* Change per-mount flags on an existing mount */
static int bind_remount_one(const char *path, unsigned long orig_flags, unsigned long new_flags, unsigned long flags_mask) {
if (mount(NULL, path, NULL, (orig_flags & ~flags_mask) | MS_REMOUNT | MS_BIND | new_flags, NULL) < 0)
return -errno;
return 0;
}
static int make_read_only(const MountEntry *m, char **blacklist, FILE *proc_self_mountinfo) {
unsigned long new_flags = 0, flags_mask = 0;
bool submounts = false;
@ -1102,7 +1094,7 @@ static int make_read_only(const MountEntry *m, char **blacklist, FILE *proc_self
if (submounts)
r = bind_remount_recursive_with_mountinfo(mount_entry_path(m), new_flags, flags_mask, blacklist, proc_self_mountinfo);
else
r = bind_remount_one(mount_entry_path(m), m->flags, new_flags, flags_mask);
r = bind_remount_one_with_mountinfo(mount_entry_path(m), new_flags, flags_mask, proc_self_mountinfo);
/* Not that we only turn on the MS_RDONLY flag here, we never turn it off. Something that was marked
* read-only already stays this way. This improves compatibility with container managers, where we

122
src/shared/mount-util.c
View File

@ -76,35 +76,57 @@ int umount_recursive(const char *prefix, int flags) {
return n;
}
/* Get the mount flags for the mountpoint at "path" from "table" */
static int get_mount_flags(const char *path, unsigned long *flags, struct libmnt_table *table) {
struct statvfs buf = {};
struct libmnt_fs *fs = NULL;
const char *opts = NULL;
static int get_mount_flags(
struct libmnt_table *table,
const char *path,
unsigned long *ret) {
struct libmnt_fs *fs;
struct statvfs buf;
const char *opts;
int r = 0;
/* Get the mount flags for the mountpoint at "path" from "table". We have a fallback using statvfs()
* in place (which provides us with mostly the same info), but it's just a fallback, since using it
* means triggering autofs or NFS mounts, which we'd rather avoid needlessly. */
fs = mnt_table_find_target(table, path, MNT_ITER_FORWARD);
if (!fs) {
log_warning("Could not find '%s' in mount table", path);
log_debug("Could not find '%s' in mount table, ignoring.", path);
goto fallback;
}
opts = mnt_fs_get_vfs_options(fs);
r = mnt_optstr_get_flags(opts, flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
if (!opts) {
*ret = 0;
return 0;
}
r = mnt_optstr_get_flags(opts, ret, mnt_get_builtin_optmap(MNT_LINUX_MAP));
if (r != 0) {
log_warning_errno(r, "Could not get flags for '%s': %m", path);
log_debug_errno(r, "Could not get flags for '%s', ignoring: %m", path);
goto fallback;
}
/* relatime is default and trying to set it in an unprivileged container causes EPERM */
*flags &= ~MS_RELATIME;
/* MS_RELATIME is default and trying to set it in an unprivileged container causes EPERM */
*ret &= ~MS_RELATIME;
return 0;
fallback:
if (statvfs(path, &buf) < 0)
return -errno;
*flags = buf.f_flag;
/* The statvfs() flags and the mount flags mostly have the same values, but for some cases do
* not. Hence map the flags manually. (Strictly speaking, ST_RELATIME/MS_RELATIME is the most
* prominent one that doesn't match, but that's the one we mask away anyway, see above.) */
*ret =
FLAGS_SET(buf.f_flag, ST_RDONLY) * MS_RDONLY |
FLAGS_SET(buf.f_flag, ST_NODEV) * MS_NODEV |
FLAGS_SET(buf.f_flag, ST_NOEXEC) * MS_NOEXEC |
FLAGS_SET(buf.f_flag, ST_NOSUID) * MS_NOSUID |
FLAGS_SET(buf.f_flag, ST_NOATIME) * MS_NOATIME |
FLAGS_SET(buf.f_flag, ST_NODIRATIME) * MS_NODIRATIME;
return 0;
}
@ -118,9 +140,10 @@ int bind_remount_recursive_with_mountinfo(
FILE *proc_self_mountinfo) {
_cleanup_set_free_free_ Set *done = NULL;
_cleanup_free_ char *cleaned = NULL;
_cleanup_free_ char *simplified = NULL;
int r;
assert(prefix);
assert(proc_self_mountinfo);
/* Recursively remount a directory (and all its submounts) read-only or read-write. If the directory is already
@ -134,11 +157,11 @@ int bind_remount_recursive_with_mountinfo(
* If the "blacklist" parameter is specified it may contain a list of subtrees to exclude from the
* remount operation. Note that we'll ignore the blacklist for the top-level path. */
cleaned = strdup(prefix);
if (!cleaned)
simplified = strdup(prefix);
if (!simplified)
return -ENOMEM;
path_simplify(cleaned, false);
path_simplify(simplified, false);
done = set_new(&path_hash_ops);
if (!done)
@ -177,26 +200,26 @@ int bind_remount_recursive_with_mountinfo(
if (!path || !type)
continue;
if (!path_startswith(path, cleaned))
if (!path_startswith(path, simplified))
continue;
/* Ignore this mount if it is blacklisted, but only if it isn't the top-level mount
* we shall operate on. */
if (!path_equal(path, cleaned)) {
if (!path_equal(path, simplified)) {
bool blacklisted = false;
char **i;
STRV_FOREACH(i, blacklist) {
if (path_equal(*i, cleaned))
if (path_equal(*i, simplified))
continue;
if (!path_startswith(*i, cleaned))
if (!path_startswith(*i, simplified))
continue;
if (path_startswith(path, *i)) {
blacklisted = true;
log_debug("Not remounting %s blacklisted by %s, called for %s",
path, *i, cleaned);
path, *i, simplified);
break;
}
}
@ -211,7 +234,7 @@ int bind_remount_recursive_with_mountinfo(
* already triggered, then we will find
* another entry for this. */
if (streq(type, "autofs")) {
top_autofs = top_autofs || path_equal(path, cleaned);
top_autofs = top_autofs || path_equal(path, simplified);
continue;
}
@ -226,25 +249,24 @@ int bind_remount_recursive_with_mountinfo(
* the root is either already done, or an autofs, we
* are done */
if (set_isempty(todo) &&
(top_autofs || set_contains(done, cleaned)))
(top_autofs || set_contains(done, simplified)))
return 0;
if (!set_contains(done, cleaned) &&
!set_contains(todo, cleaned)) {
if (!set_contains(done, simplified) &&
!set_contains(todo, simplified)) {
/* The prefix directory itself is not yet a mount, make it one. */
if (mount(cleaned, cleaned, NULL, MS_BIND|MS_REC, NULL) < 0)
if (mount(simplified, simplified, NULL, MS_BIND|MS_REC, NULL) < 0)
return -errno;
orig_flags = 0;
(void) get_mount_flags(cleaned, &orig_flags, table);
orig_flags &= ~MS_RDONLY;
(void) get_mount_flags(table, simplified, &orig_flags);
if (mount(NULL, cleaned, NULL, (orig_flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags, NULL) < 0)
if (mount(NULL, simplified, NULL, (orig_flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags, NULL) < 0)
return -errno;
log_debug("Made top-level directory %s a mount point.", prefix);
r = set_put_strdup(done, cleaned);
r = set_put_strdup(done, simplified);
if (r < 0)
return r;
}
@ -278,8 +300,7 @@ int bind_remount_recursive_with_mountinfo(
/* Try to reuse the original flag set */
orig_flags = 0;
(void) get_mount_flags(x, &orig_flags, table);
orig_flags &= ~MS_RDONLY;
(void) get_mount_flags(table, x, &orig_flags);
if (mount(NULL, x, NULL, (orig_flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags, NULL) < 0)
return -errno;
@ -289,7 +310,12 @@ int bind_remount_recursive_with_mountinfo(
}
}
int bind_remount_recursive(const char *prefix, unsigned long new_flags, unsigned long flags_mask, char **blacklist) {
int bind_remount_recursive(
const char *prefix,
unsigned long new_flags,
unsigned long flags_mask,
char **blacklist) {
_cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
int r;
@ -300,6 +326,38 @@ int bind_remount_recursive(const char *prefix, unsigned long new_flags, unsigned
return bind_remount_recursive_with_mountinfo(prefix, new_flags, flags_mask, blacklist, proc_self_mountinfo);
}
int bind_remount_one_with_mountinfo(
const char *path,
unsigned long new_flags,
unsigned long flags_mask,
FILE *proc_self_mountinfo) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
unsigned long orig_flags = 0;
int r;
assert(path);
assert(proc_self_mountinfo);
rewind(proc_self_mountinfo);
table = mnt_new_table();
if (!table)
return -ENOMEM;
r = mnt_table_parse_stream(table, proc_self_mountinfo, "/proc/self/mountinfo");
if (r < 0)
return r;
/* Try to reuse the original flag set */
(void) get_mount_flags(table, path, &orig_flags);
if (mount(NULL, path, NULL, (orig_flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags, NULL) < 0)
return -errno;
return 0;
}
int mount_move_root(const char *path) {
assert(path);

1
src/shared/mount-util.h
View File

@ -10,6 +10,7 @@ int repeat_unmount(const char *path, int flags);
int umount_recursive(const char *target, int flags);
int bind_remount_recursive(const char *prefix, unsigned long new_flags, unsigned long flags_mask, char **blacklist);
int bind_remount_recursive_with_mountinfo(const char *prefix, unsigned long new_flags, unsigned long flags_mask, char **blacklist, FILE *proc_self_mountinfo);
int bind_remount_one_with_mountinfo(const char *path, unsigned long new_flags, unsigned long flags_mask, FILE *proc_self_mountinfo);
int mount_move_root(const char *path);