core: add ability to define arbitrary bind mounts for services

This adds two new settings BindPaths= and BindReadOnlyPaths=. They allow
defining arbitrary bind mounts specific to particular services. This is
particularly useful for services with RootDirectory= set as this permits making
specific bits of the host directory available to chrooted services.

The two new settings follow the concepts nspawn already possess in --bind= and
--bind-ro=, as well as the .nspawn settings Bind= and BindReadOnly= (and these
latter options should probably be renamed to BindPaths= and BindReadOnlyPaths=
too).

Fixes: #3439

1 files changed, 127 insertions, 0 deletions

diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index a2e7097de0..f325d853c6 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -3891,6 +3891,132 @@ int config_parse_namespace_path_strv(
         return 0;
 }
 
+int config_parse_bind_paths(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        ExecContext *c = data;
+        const char *p;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        if (isempty(rvalue)) {
+                /* Empty assignment resets the list */
+                bind_mount_free_many(c->bind_mounts, c->n_bind_mounts);
+                c->bind_mounts = NULL;
+                c->n_bind_mounts = 0;
+                return 0;
+        }
+
+        p = rvalue;
+        for (;;) {
+                _cleanup_free_ char *source = NULL, *destination = NULL;
+                char *s = NULL, *d = NULL;
+                bool rbind = true, ignore_enoent = false;
+
+                r = extract_first_word(&p, &source, ":" WHITESPACE, EXTRACT_QUOTES|EXTRACT_DONT_COALESCE_SEPARATORS);
+                if (r == 0)
+                        break;
+                if (r == -ENOMEM)
+                        return log_oom();
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse %s: %s", lvalue, rvalue);
+                        return 0;
+                }
+
+                s = source;
+                if (s[0] == '-') {
+                        ignore_enoent = true;
+                        s++;
+                }
+
+                if (!utf8_is_valid(s)) {
+                        log_syntax_invalid_utf8(unit, LOG_ERR, filename, line, s);
+                        return 0;
+                }
+                if (!path_is_absolute(s)) {
+                        log_syntax(unit, LOG_ERR, filename, line, 0, "Not an absolute source path, ignoring: %s", s);
+                        return 0;
+                }
+
+                path_kill_slashes(s);
+
+                /* Optionally, the destination is specified. */
+                if (p && p[-1] == ':') {
+                        r = extract_first_word(&p, &destination, ":" WHITESPACE, EXTRACT_QUOTES|EXTRACT_DONT_COALESCE_SEPARATORS);
+                        if (r == -ENOMEM)
+                                return log_oom();
+                        if (r < 0) {
+                                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse %s: %s", lvalue, rvalue);
+                                return 0;
+                        }
+                        if (r == 0) {
+                                log_syntax(unit, LOG_ERR, filename, line, 0, "Missing argument after ':': %s", rvalue);
+                                return 0;
+                        }
+
+                        if (!utf8_is_valid(destination)) {
+                                log_syntax_invalid_utf8(unit, LOG_ERR, filename, line, destination);
+                                return 0;
+                        }
+                        if (!path_is_absolute(destination)) {
+                                log_syntax(unit, LOG_ERR, filename, line, 0, "Not an absolute destination path, ignoring: %s", destination);
+                                return 0;
+                        }
+
+                        d = path_kill_slashes(destination);
+
+                        /* Optionally, there's also a short option string specified */
+                        if (p && p[-1] == ':') {
+                                _cleanup_free_ char *options = NULL;
+
+                                r = extract_first_word(&p, &options, NULL, EXTRACT_QUOTES);
+                                if (r == -ENOMEM)
+                                        return log_oom();
+                                if (r < 0) {
+                                        log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse %s: %s", lvalue, rvalue);
+                                        return 0;
+                                }
+
+                                if (isempty(options) || streq(options, "rbind"))
+                                        rbind = true;
+                                else if (streq(options, "norbind"))
+                                        rbind = false;
+                                else {
+                                        log_syntax(unit, LOG_ERR, filename, line, 0, "Invalid option string, ignoring setting: %s", options);
+                                        return 0;
+                                }
+                        }
+                } else
+                        d = s;
+
+                r = bind_mount_add(&c->bind_mounts, &c->n_bind_mounts,
+                                   &(BindMount) {
+                                           .source = s,
+                                           .destination = d,
+                                           .read_only = !!strstr(lvalue, "ReadOnly"),
+                                           .recursive = rbind,
+                                           .ignore_enoent = ignore_enoent,
+                                   });
+                if (r < 0)
+                        return log_oom();
+        }
+
+        return 0;
+}
+
 int config_parse_no_new_privileges(
                 const char* unit,
                 const char *filename,
@@ -4388,6 +4514,7 @@ void unit_dump_config_items(FILE *f) {
                 { config_parse_sec,                   "SECONDS" },
                 { config_parse_nsec,                  "NANOSECONDS" },
                 { config_parse_namespace_path_strv,   "PATH [...]" },
+                { config_parse_bind_paths,            "PATH[:PATH[:OPTIONS]] [...]" },
                 { config_parse_unit_requires_mounts_for, "PATH [...]" },
                 { config_parse_exec_mount_flags,      "MOUNTFLAG [...]" },
                 { config_parse_unit_string_printf,    "STRING" },