Merge pull request #24784 from yuwata/core-exec-directory

core: do not create symlink to private directory if parent already exists

src/core/execute.c

@@ -91,6 +91,7 @@
 #include "signal-util.h"
 #include "smack-util.h"
 #include "socket-util.h"
+#include "sort-util.h"
 #include "special.h"
 #include "stat-util.h"
 #include "string-table.h"
@@ -2412,12 +2413,24 @@ static int setup_exec_directory(
                                         goto fail;
                         }
 
-                        /* And link it up from the original place. Note that if a mount namespace is going to be
-                         * used, then this symlink remains on the host, and a new one for the child namespace will
-                         * be created later. */
-                        r = symlink_idempotent(pp, p, true);
-                        if (r < 0)
-                                goto fail;
+                        if (!context->directories[type].items[i].only_create) {
+                                /* And link it up from the original place.
+                                 * Notes
+                                 * 1) If a mount namespace is going to be used, then this symlink remains on
+                                 *    the host, and a new one for the child namespace will be created later.
+                                 * 2) It is not necessary to create this symlink when one of its parent
+                                 *    directories is specified and already created. E.g.
+                                 *        StateDirectory=foo foo/bar
+                                 *    In that case, the inode points to pp and p for "foo/bar" are the same:
+                                 *        pp = "/var/lib/private/foo/bar"
+                                 *        p = "/var/lib/foo/bar"
+                                 *    and, /var/lib/foo is a symlink to /var/lib/private/foo. So, not only
+                                 *    we do not need to create the symlink, but we cannot create the symlink.
+                                 *    See issue #24783. */
+                                r = symlink_idempotent(pp, p, true);
+                                if (r < 0)
+                                        goto fail;
+                        }
 
                 } else {
                         _cleanup_free_ char *target = NULL;
@@ -3289,7 +3302,8 @@ static int compile_bind_mounts(
                 if (!params->prefix[t])
                         continue;
 
-                n += context->directories[t].n_items;
+                for (size_t i = 0; i < context->directories[t].n_items; i++)
+                        n += !context->directories[t].items[i].only_create;
         }
 
         if (n <= 0) {
@@ -3358,6 +3372,11 @@ static int compile_bind_mounts(
                 for (size_t i = 0; i < context->directories[t].n_items; i++) {
                         char *s, *d;
 
+                        /* When one of the parent directories is in the list, we cannot create the symlink
+                         * for the child directory. See also the comments in setup_exec_directory(). */
+                        if (context->directories[t].items[i].only_create)
+                                continue;
+
                         if (exec_directory_is_private(context, t))
                                 s = path_join(params->prefix[t], "private", context->directories[t].items[i].path);
                         else
@@ -3437,7 +3456,9 @@ static int compile_symlinks(
                                         return r;
                         }
 
-                        if (!exec_directory_is_private(context, dt) || exec_context_with_rootfs(context))
+                        if (!exec_directory_is_private(context, dt) ||
+                            exec_context_with_rootfs(context) ||
+                            context->directories[dt].items[i].only_create)
                                 continue;
 
                         private_path = path_join(params->prefix[dt], "private", context->directories[dt].items[i].path);
@@ -7041,33 +7062,82 @@ void exec_directory_done(ExecDirectory *d) {
         d->mode = 0755;
 }
 
-int exec_directory_add(ExecDirectoryItem **d, size_t *n, const char *path, char **symlinks) {
+static ExecDirectoryItem *exec_directory_find(ExecDirectory *d, const char *path) {
+        assert(d);
+        assert(path);
+
+        for (size_t i = 0; i < d->n_items; i++)
+                if (path_equal(d->items[i].path, path))
+                        return &d->items[i];
+
+        return NULL;
+}
+
+int exec_directory_add(ExecDirectory *d, const char *path, const char *symlink) {
         _cleanup_strv_free_ char **s = NULL;
         _cleanup_free_ char *p = NULL;
+        ExecDirectoryItem *existing;
+        int r;
 
         assert(d);
-        assert(n);
         assert(path);
 
+        existing = exec_directory_find(d, path);
+        if (existing) {
+                r = strv_extend(&existing->symlinks, symlink);
+                if (r < 0)
+                        return r;
+
+                return 0; /* existing item is updated */
+        }
+
         p = strdup(path);
         if (!p)
                 return -ENOMEM;
 
-        if (symlinks) {
-                s = strv_copy(symlinks);
+        if (symlink) {
+                s = strv_new(symlink);
                 if (!s)
                         return -ENOMEM;
         }
 
-        if (!GREEDY_REALLOC(*d, *n + 1))
+        if (!GREEDY_REALLOC(d->items, d->n_items + 1))
                 return -ENOMEM;
 
-        (*d)[(*n) ++] = (ExecDirectoryItem) {
+        d->items[d->n_items++] = (ExecDirectoryItem) {
                 .path = TAKE_PTR(p),
                 .symlinks = TAKE_PTR(s),
         };
 
-        return 0;
+        return 1; /* new item is added */
+}
+
+static int exec_directory_item_compare_func(const ExecDirectoryItem *a, const ExecDirectoryItem *b) {
+        assert(a);
+        assert(b);
+
+        return path_compare(a->path, b->path);
+}
+
+void exec_directory_sort(ExecDirectory *d) {
+        assert(d);
+
+        /* Sort the exec directories to make always parent directories processed at first in
+         * setup_exec_directory(), e.g., even if StateDirectory=foo/bar foo, we need to create foo at first,
+         * then foo/bar. Also, set .only_create flag if one of the parent directories is contained in the
+         * list. See also comments in setup_exec_directory() and issue #24783. */
+
+        if (d->n_items <= 1)
+                return;
+
+        typesafe_qsort(d->items, d->n_items, exec_directory_item_compare_func);
+
+        for (size_t i = 1; i < d->n_items; i++)
+                for (size_t j = 0; j < i; j++)
+                        if (path_startswith(d->items[i].path, d->items[j].path)) {
+                                d->items[i].only_create = true;
+                                break;
+                        }
 }
 
 DEFINE_HASH_OPS_WITH_VALUE_DESTRUCTOR(exec_set_credential_hash_ops, char, string_hash_func, string_compare_func, ExecSetCredential, exec_set_credential_free);