Merge branch 'fix/audit-receiver' into fix/audit-cycle

src/shared/file.c

@@ -1136,17 +1136,51 @@ int file_open_private_dir(const char* dir_path) {
   return fd;
 }
 
-/* Open a --temp-dir scratch directory exactly as rsync does: the directory must
- * already exist and is used as given (an absolute path is used verbatim, a
- * relative one was already resolved against the destination root by the
- * caller).  Unlike file_open_private_dir this neither creates it nor confines
- * it below the receive root, because rsync accepts any temp dir -- including
- * one outside the destination tree or on another filesystem.  Returns an
- * O_DIRECTORY|O_CLOEXEC fd, or -1 on error. */
+/* Open a --temp-dir scratch directory.  The directory must already exist (rsync
+ * never creates it); a relative path was already resolved against the
+ * destination root by the caller.  Unlike file_open_private_dir this neither
+ * creates it nor requires it to be a direct child of the receive root, because
+ * rsync permits a scratch dir that (via a symlink) lands on another filesystem
+ * -- but it MUST resolve inside the authorized receive root.  The directory is
+ * opened following symlinks and then judged by the REAL path of the opened fd
+ * (through /proc/self/fd), so a client-planted symlink under the receive root
+ * can never redirect receiver scratch files outside the sandbox while an
+ * in-root link to another filesystem (the EXDEV fallback case) still works.
+ * Returns an O_DIRECTORY|O_CLOEXEC fd, or -1 on error (errno set; an escaping
+ * target is reported as EACCES with a logged reason). */
 int file_open_temp_dir(const char* dir_path) {
   if (!dir_path)
     return -1;
-  return open(dir_path, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+  int fd = open(dir_path, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+  if (fd < 0)
+    return -1;
+  const char* root = utils_get_authorized_root_path();
+  if (!root) {
+    /* No authorized root (e.g. a local batch apply): nothing to confine
+       against, so preserve the historical open-as-given behavior. */
+    return fd;
+  }
+  char fd_path[64];
+  int fd_path_length = snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", fd);
+  char resolved[PATH_MAX];
+  if (fd_path_length < 0 || (size_t)fd_path_length >= sizeof(fd_path) ||
+      !realpath(fd_path, resolved)) {
+    int saved_errno = errno;
+    close(fd);
+    errno = saved_errno;
+    return -1;
+  }
+  if (!path_is_within_root(root, resolved)) {
+    char* escaped = output_escape(dir_path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_ERROR,
+                "--temp-dir '%s' resolves outside the authorized receive root; refusing",
+                escaped ? escaped : "<allocation failed>");
+    free(escaped);
+    close(fd);
+    errno = EACCES;
+    return -1;
+  }
+  return fd;
 }
 
 /* After the content and mode/times are restored on the just-written file, apply
@@ -1859,6 +1893,6 @@ bool file_write_to_disk(const char* path, const void* data, unsigned long long d
                         bool inplace, bool sparse) {
   if (!path || (!data && data_size != 0) || has_path_traversal(path))
     return false;
-  FileAttrPolicy policy = {false, false, false, false};
+  FileAttrPolicy policy = {0};
   return file_to_disk_secure(path, data, data_size, inplace, sparse, false, NULL, policy, NULL);
 }

src/shared/file.h

@@ -103,8 +103,12 @@ bool file_remove_tree_secure(const char* path);
    the authorized root.  Used for the --delay-updates staging directory. */
 int file_open_private_dir(const char* dir_path);
 
-/* Open an existing --temp-dir scratch directory as-is (absolute or relative;
-   no creation, no root confinement), matching rsync's --temp-dir handling. */
+/* Open an existing --temp-dir scratch directory (relative or absolute; no
+   creation).  When an authorized receive root is configured the directory's
+   REAL path (symlinks resolved) must lie within it, so a client-planted
+   symlink cannot redirect receiver scratch files outside the sandbox; an
+   in-root symlink to another filesystem is still allowed for rsync's EXDEV
+   fallback. */
 int file_open_temp_dir(const char* dir_path);
 
 /* The file_to_disk_secure* variants write a temporary copy in the destination

src/shared/file_attr.h

@@ -29,6 +29,12 @@ typedef struct FileAttrPolicy {
   bool times;         /* config->preserve_times: apply the source mtime */
   bool atimes;        /* config->preserve_atimes (-U): apply the source atime */
   bool executability; /* config->use_executability (-E): exec-bits-only mode */
+  /* privilege_super_mode_permitted(): when false (SUPER_MODE_OFF / --no-super,
+     or a daemon that did not grant `client owner = yes`), the setuid/setgid/
+     sticky bits are stripped from every applied mode (source mode and any
+     --chmod result) even under --perms.  When true, rsync's exact semantics are
+     preserved: -p copies the special bits and the kernel decides. */
+  bool super_permitted;
 } FileAttrPolicy;
 
 /* Build the per-attribute policy from a connection's Config.  A NULL config

src/shared/file_receive.c

@@ -474,9 +474,13 @@ static FileSaveResult file_save_special_to_disk(const char* root_directory, cons
   /* Under -p/--perms rsync copies the source's permission and special bits; a
    * kernel that denies setuid/setgid/sticky reports the failure rather than
    * having them masked here.  Without -p the node is created like any other new
-   * entry: source_mode & 0777 & ~umask. */
+   * entry: source_mode & 0777 & ~umask.  When super-user activities are
+   * forbidden, the special bits are stripped even under -p (they are
+   * super-user activities just like device-node creation). */
   mode_t perms = config->preserve_perms ? (mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777))
                                         : (mode & 0777 & ~(mode_t)file_process_umask());
+  if (!privilege_super_mode_permitted(config->super_mode))
+    perms &= ~(mode_t)(S_ISUID | S_ISGID | S_ISVTX);
 
   int rc = is_fifo ? mkfifoat(parent_fd, leaf, perms)
                    : mknodat(parent_fd, leaf, create_mode | perms, rdev);
@@ -2949,8 +2953,12 @@ void dir_metadata_list_apply(const DirTimeList* list, const char* root_directory
       }
       if (mode_ready) {
         /* rsync -p copies the source directory mode exactly, including
-         * group/other write and the setgid/sticky bits. */
+         * group/other write and the setgid/sticky bits.  Setuid/setgid/sticky
+         * are super-user activities: when the connection forbade them
+         * (SUPER_MODE_OFF / --no-super), strip them even under -p. */
         mode_t safe_mode = dir_mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+        if (!privilege_super_mode_permitted(config->super_mode))
+          safe_mode &= ~(mode_t)(S_ISUID | S_ISGID | S_ISVTX);
         if (dir_fd < 0) {
           char* escaped_path = output_escape(dir_path, log_get_8_bit_output());
           log_message(LOG_LEVEL_WARNING, "Failed to open directory %s to set its mode: %s",

src/shared/metadata.c

@@ -211,13 +211,22 @@ FileMetadata* metadata_receive(int file_descriptor, int* ok) {
 
 bool metadata_mode_for_policy(mode_t source_mode, mode_t current_mode, FileAttrPolicy policy,
                               mode_t* out_mode) {
+  const mode_t special_bits = (mode_t)(S_ISUID | S_ISGID | S_ISVTX);
   const mode_t execute_bits = S_IXUSR | S_IXGRP | S_IXOTH;
   if (policy.perms) {
     /* rsync --perms copies the source's permission and special bits exactly,
      * including group/other write and setuid/setgid/sticky.  The kernel may
      * still clear setgid when the receiver is not in the file's group; the
-     * caller logs a failed chmod rather than silently masking the bits here. */
-    *out_mode = source_mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+     * caller logs a failed chmod rather than silently masking the bits here.
+     * Setuid/setgid/sticky are super-user activities: when the connection did
+     * not permit them (SUPER_MODE_OFF / --no-super) they are stripped, so a
+     * client can never install a privileged bit on a receiver that forbade
+     * super-user activities.  This also covers bits introduced by --chmod,
+     * whose result is fed in as source_mode. */
+    mode_t bits = source_mode & (mode_t)(special_bits | 0777);
+    if (!policy.super_permitted)
+      bits &= ~special_bits;
+    *out_mode = bits;
     return true;
   }
   if (policy.executability) {
@@ -227,8 +236,11 @@ bool metadata_mode_for_policy(mode_t source_mode, mode_t current_mode, FileAttrP
      * execute); otherwise clear every execute bit.  This runs on the
      * destination-derived base (pre-existing dest mode, or source&~umask for a
      * new file), and leaves the special bits untouched.  --perms wins when both
-     * are set (handled above). */
-    mode_t base = current_mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+     * are set (handled above).  The destination's own special bits survive
+     * unless super-user activities are forbidden. */
+    mode_t base = current_mode & (mode_t)(special_bits | 0777);
+    if (!policy.super_permitted)
+      base &= ~special_bits;
     if (source_mode & 0111)
       *out_mode = base | ((base & 0444) >> 2);
     else
@@ -240,12 +252,13 @@ bool metadata_mode_for_policy(mode_t source_mode, mode_t current_mode, FileAttrP
 }
 
 FileAttrPolicy file_attr_policy_from_config(const Config* config) {
-  FileAttrPolicy policy = {false, false, false, false};
+  FileAttrPolicy policy = {0};
   if (config) {
     policy.perms = config->preserve_perms;
     policy.times = config->preserve_times;
     policy.atimes = config->preserve_atimes;
     policy.executability = config->use_executability;
+    policy.super_permitted = privilege_super_mode_permitted(config->super_mode);
   }
   return policy;
 }
@@ -314,6 +327,8 @@ bool file_restore_symlink_metadata(const char* path, const FileMetadata* metadat
      transfer never fails over it. */
   if (policy.perms) {
     mode_t link_mode = metadata->mode & (mode_t)(S_ISUID | S_ISGID | S_ISVTX | 0777);
+    if (!policy.super_permitted)
+      link_mode &= ~(mode_t)(S_ISUID | S_ISGID | S_ISVTX);
     if (fchmodat(parent_fd, leaf, link_mode, AT_SYMLINK_NOFOLLOW) != 0 && errno != EOPNOTSUPP &&
         errno != ENOTSUP && errno != ENOSYS) {
       log_message(LOG_LEVEL_DEBUG, "Could not set symlink mode on %s: %s", path, strerror(errno));