From b0edc606618e02baff5c454151e1fcc5c70b917c Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Mon, 31 Aug 2026 17:13:59 +0200 Subject: [PATCH] dissect: optionally allow attaching images that do not qualify as DDIs with --attach It's nice to use --attach since it validates our images. So far, it strictly insisted on checking that the image was a DDI however, which limits its use for certain usecases. Add "--relax" to address this limitation. --- man/systemd-dissect.xml | 15 ++++++++- shell-completion/bash/systemd-dissect | 3 +- src/dissect/dissect.c | 47 +++++++++++++++++---------- test/units/TEST-50-DISSECT.dissect.sh | 12 +++++++ 4 files changed, 58 insertions(+), 19 deletions(-) diff --git a/man/systemd-dissect.xml b/man/systemd-dissect.xml index b4ff042bb9..670fb2a574 100644 --- a/man/systemd-dissect.xml +++ b/man/systemd-dissect.xml @@ -209,7 +209,8 @@ of losetup --find --show --partscan, but will validate the image as DDI before attaching, and derive the correct sector size to use automatically. Moreover, it ensures the per-partition block devices are created before returning and attempts to enable direct IO mode, if - possible. Takes a path to a disk image file. + possible. Takes a path to a disk image file. Use to attach images that do + not qualify as DDI. If combined with output of the block device name is suppressed. @@ -541,6 +542,18 @@ + + + + If combined with , skips validation of the image and + attaches it to the loopback block device as it is, even if it does not qualify as DDI. If this + switch is used, no image dissection takes place, and thus it is not guaranteed that the + per-partition block devices are created before the command returns. May not be combined with any + other command than . + + + + diff --git a/shell-completion/bash/systemd-dissect b/shell-completion/bash/systemd-dissect index a9fa639c3f..10366b38f1 100644 --- a/shell-completion/bash/systemd-dissect +++ b/shell-completion/bash/systemd-dissect @@ -37,7 +37,8 @@ _systemd_dissect() { -r --read-only --mkdir --rmdir - --in-memory' + --in-memory + --relax' [ARG]='-m --mount -M -u --umount -U --attach diff --git a/src/dissect/dissect.c b/src/dissect/dissect.c index 29bf421819..f024fe2050 100644 --- a/src/dissect/dissect.c +++ b/src/dissect/dissect.c @@ -109,6 +109,7 @@ static RuntimeScope arg_runtime_scope = _RUNTIME_SCOPE_INVALID; static bool arg_all = false; static uid_t arg_uid_base = UID_INVALID; static bool arg_quiet = false; +static bool arg_relax = false; static ImageFilter *arg_image_filter = NULL; static int arg_copy_ownership = -1; @@ -355,6 +356,10 @@ static int parse_argv(int argc, char *argv[]) { arg_loop_ref_auto = true; break; + OPTION_LONG("relax", NULL, "Skip DDI validation, attach image as it is"): + arg_relax = true; + break; + OPTION_LONG("image-policy", "POLICY", "Specify image dissection policy"): r = parse_image_policy_argument(opts.arg, &arg_image_policy); if (r < 0) @@ -707,6 +712,10 @@ static int parse_argv(int argc, char *argv[]) { return r; } + if (arg_relax && arg_action != ACTION_ATTACH) + return log_error_errno(SYNTHETIC_ERRNO(EINVAL), + "The --relax switch is only supported in combination with --attach."); + SET_FLAG(arg_flags, DISSECT_IMAGE_ALLOW_INTERACTIVE_AUTH, isatty_safe(STDIN_FILENO)); return 1; @@ -1809,19 +1818,16 @@ static int action_discover(void) { return table_print_with_pager(t, arg_json_format_flags, arg_pager_flags, arg_legend); } -static int action_attach(DissectedImage *m, LoopDevice *d) { +static int action_attach(LoopDevice *d) { int r; - assert(m); assert(d); r = loop_device_set_autoclear(d, false); if (r < 0) return log_error_errno(r, "Failed to disable auto-clear logic on loopback device: %m"); - r = dissected_image_relinquish(m); - if (r < 0) - return log_error_errno(r, "Failed to relinquish DM and loopback block devices: %m"); + loop_device_relinquish(d); if (!arg_quiet) puts(d->node); @@ -1997,7 +2003,7 @@ static int run(int argc, char *argv[]) { ; } - if (arg_image) { + if (arg_image && !arg_relax) { r = verity_settings_load( &arg_verity_settings, arg_image, @@ -2053,19 +2059,26 @@ static int run(int argc, char *argv[]) { log_warning_errno(r, "Failed to set loop reference string to '%s', ignoring: %m", arg_loop_ref); } - r = dissect_loop_device_and_warn( - d, - &arg_verity_settings, - /* mount_options= */ NULL, - arg_image_policy, - arg_image_filter, - arg_flags, - &m); - if (r < 0) - return r; + /* Unless --relax is specified we insist that the image qualifies as DDI: + * dissecting it validates it against the image policy and waits until the + * kernel created the per-partition block devices, so that callers may + * access them immediately after we return. With --relax we skip dissection + * entirely, and attach the image as it is. */ + if (!arg_relax) { + r = dissect_loop_device_and_warn( + d, + &arg_verity_settings, + /* mount_options= */ NULL, + arg_image_policy, + arg_image_filter, + arg_flags, + &m); + if (r < 0) + return r; + } if (arg_action == ACTION_ATTACH) - return action_attach(m, d); + return action_attach(d); r = dissected_image_load_verity_sig_partition( m, diff --git a/test/units/TEST-50-DISSECT.dissect.sh b/test/units/TEST-50-DISSECT.dissect.sh index a8908fcfef..7a1e7daa3b 100755 --- a/test/units/TEST-50-DISSECT.dissect.sh +++ b/test/units/TEST-50-DISSECT.dissect.sh @@ -1066,6 +1066,18 @@ test ! -e "/dev/disk/by-loop-ref/$name" systemd-dissect --detach "$MINIMAL_IMAGE.raw" (! systemd-dissect --detach "$MINIMAL_IMAGE.raw") +# --attach --relax also works on images that do not qualify as DDI, e.g. an entirely blank one +BLANK_IMAGE="$(mktemp /var/tmp/blankXXX.raw)" +truncate -s 16M "$BLANK_IMAGE" +(! systemd-dissect --attach "$BLANK_IMAGE") +LOOP="$(systemd-dissect --attach --relax "$BLANK_IMAGE")" +test -b "$LOOP" +systemd-dissect --detach "$LOOP" +rm -f "$BLANK_IMAGE" + +# --relax makes no sense for the other verbs +(! systemd-dissect --relax "$MINIMAL_IMAGE.raw") + # check for confext functionality mkdir -p /run/confexts/test/etc/extension-release.d echo "ID=_any" >/run/confexts/test/etc/extension-release.d/extension-release.test