Release 2.76.3: changelogs (#17393)

Merge changelogs back into master, please use a regular “merge” to merge
it.

Author: sergiocazzolato

NEWS.md

@@ -1,3 +1,20 @@
+# New in snapd 2.76.3
+* FDE: support keyboard configuration at install-time for first-boot
+* FDE: re-enable passphrases/PINs at install-time
+* FDE: require volumes authentication if HWROT is missing
+* FDE: bump secboot to rev 457b03a16d19
+* FDE: use new secboot API for reprovision TPM
+* Cross-distro: modify SELinux policy to use init_named_socket_activation() for allowing systemd to start snapd through socket activation
+* packaging: make sure that usr/bin/snap is built with correct build tags on debian sid
+* Ensure profiles are setup before running prepare-{slot, plug}* hooks
+
+# New in snapd 2.76.2
+* interfaces: steam-support, docker-support | fix mountinfo denial
+
+# New in snapd 2.76.1
+* LP: #2067006 CVE-2024-5300
+* CVE-2026-3888
+
 # New in snapd 2.76
 * assertions: add helper for validating integrity data
 * assertions: drop incorrect/non-standard Ed25519 support

cmd/snap-confine/mount-support.c

@@ -86,20 +86,8 @@ static void setup_private_tmp(const char *snap_instance) {
     int base_dir_fd SC_CLEANUP(sc_cleanup_close) = -1;
     int tmp_dir_fd SC_CLEANUP(sc_cleanup_close) = -1;
 
-    // /tmp/snap-private-tmp should have already been created by
-    // systemd-tmpfiles but we can try create it anyway since snapd may have
-    // just been installed in which case the tmpfiles conf would not have got
-    // executed yet. Internally sc_ensure_mkdir() first creates the directory
-    // with 0000 permissions and then updates its ownership and mode to 0700.
-    // Because of this, in case the directory was not present, there is a
-    // possibility for a race with another instance of snap-confine running in
-    // parallel, where one may have only created the directory with 0000
-    // permissions or owned by the user, while another observes the directory
-    // and proceeds with execution up to a point where it asserts mode bits or
-    // ownership.
-    if (sc_ensure_mkdir(SNAP_PRIVATE_TMP_ROOT_DIR, 0700, 0, 0) != 0) {
-        die("cannot create " SNAP_PRIVATE_TMP_ROOT_DIR);
-    }
+    // Open the /tmp/snap-private-tmp directory (created by packaging scripts,
+    // systemd-tmpfiles, or snapd).
     private_tmp_root_fd = open(SNAP_PRIVATE_TMP_ROOT_DIR, O_RDONLY | O_DIRECTORY | O_CLOEXEC | O_NOFOLLOW);
     if (private_tmp_root_fd < 0) {
         die("cannot open %s", SNAP_PRIVATE_TMP_ROOT_DIR);
@@ -108,35 +96,13 @@ static void setup_private_tmp(const char *snap_instance) {
     if (fstat(private_tmp_root_fd, &st) < 0) {
         die("cannot stat %s", SNAP_PRIVATE_TMP_ROOT_DIR);
     }
-    // In case we were racing with another snap-confine instance (as described
-    // earlier), the permissions or ownership we observe here may be a snapshot
-    // of an intermediate state of the directory (before its mode was updated to
-    // 0700, or still owned by the user). Test each property and amend if
-    // possible. Even if racing, another instance of snap-confine tries to reach
-    // the same state. We still have CAP_DAC_OVERRIDE, CAP_FOWNER, so we can
-    // attempt to fix the state.
     if (!S_ISDIR(st.st_mode)) {
-        // This we cannot fix
         die("%s has unexpected type", SNAP_PRIVATE_TMP_ROOT_DIR);
     }
-    // We have already verified type, check ownership.
-    if (st.st_uid != 0 || st.st_gid != 0) {
-        // May have hit a race, let's fix the ownership.
-        if (fchown(private_tmp_root_fd, 0, 0) != 0) {
-            die("%s has unexpected ownership %d:%d which could not be fixed", SNAP_PRIVATE_TMP_ROOT_DIR, st.st_uid,
-                st.st_gid);
-        }
-    }
-    // We have already verified the type and ownership, check mode.
-    if ((st.st_mode & ~S_IFMT) != 0700) {
-        // May have hit a race, let's fix the mode.
-        if (fchmod(private_tmp_root_fd, 0700) != 0) {
-            die("%s has unexpected mode 0%o which could not be fixed", SNAP_PRIVATE_TMP_ROOT_DIR, st.st_mode & ~S_IFMT);
-        }
+    if (st.st_uid != 0 || st.st_gid != 0 || st.st_mode != (S_IFDIR | 0700)) {
+        die("%s has unexpected ownership / permissions", SNAP_PRIVATE_TMP_ROOT_DIR);
     }
     // Create /tmp/snap-private-tmp/snap.$SNAP_INSTANCE_NAME/ 0700 root:root.
-    // Note that the snap is locked at this point, so a race such as when
-    // creating /tmp/snap-private-tmp would not occur.
     sc_must_snprintf(base, sizeof(base), "snap.%s", snap_instance);
     if (sc_ensure_mkdirat(private_tmp_root_fd, base, 0700, 0, 0) != 0) {
         die("cannot create base directory: %s", base);
@@ -448,7 +414,9 @@ static void sc_replicate_base_rootfs(const char *scratch_dir, const char *rootfs
             // Create an empty file which can be used as a mount point, no need
             // for 0000, parent directory already owned and writable by root
             // only.
-            int fd = open(full_path, O_CREAT | O_TRUNC, 0644);
+            // Use O_NOFOLLOW to prevent symlink attacks during the TOCTOU window
+            // between directory creation and chown.
+            int fd = open(full_path, O_CREAT | O_TRUNC | O_NOFOLLOW, 0644);
             if (fd < 0) {
                 die("cannot create mount point for file \"%s\"", full_path);
             }
@@ -506,7 +474,7 @@ static void sc_replicate_base_rootfs(const char *scratch_dir, const char *rootfs
  * snaps) or remove them, through the unmount system call.
  **/
 static void sc_bootstrap_mount_namespace(const struct sc_mount_config *config) {
-    char scratch_dir[] = "/tmp/snap.rootfs_XXXXXX";
+    char scratch_dir[] = "/tmp/snap-private-tmp/snap.rootfs_XXXXXX";
     char src[PATH_MAX] = {0};
     char dst[PATH_MAX] = {0};
     if (mkdtemp(scratch_dir) == NULL) {
@@ -765,7 +733,7 @@ static void sc_bootstrap_mount_namespace(const struct sc_mount_config *config) {
     // all-snap system where this would-be chroot didn't happen and all the
     // rules see / as the root file system _OR_ we are running on top of a
     // classic distribution and this chroot has now moved all paths to
-    // /tmp/snap.rootfs_*.
+    // /tmp/snap-private-tmp/snap.rootfs_*.
     //
     // Because we are using unshare(2) with CLONE_NEWNS we can essentially use
     // pivot_root just like chroot but this makes apparmor unaware of the old