dissect: ignore old uevents when waiting for loopback partition scan

Let's drop all monitor uevent that were enqueued before we actually
started setting up the device.

This doesn't fix the race, but it makes the race window smaller: since
we cannot determine the uevent seqnum and the loopback attachment
atomically, there's a tiny window where uevents might be generated by
the device which we mistake for being associated with out use of the
loopback device.

diff --git a/src/core/namespace.c b/src/core/namespace.c
index 9f9d47d34a2cd276161f3498f489fa96c7e357f1..bffcb5ac86e4e79b11e7373a4ba294418091ca70 100644 (file)
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -1863,6 +1863,7 @@ int setup_namespace(
                                 loop_device->fd,
                                 &verity,
                                 root_image_options,
+                                loop_device->uevent_seqnum_not_before,
                                 dissect_image_flags,
                                 &dissected_image);
                 if (r < 0)

diff --git a/src/dissect/dissect.c b/src/dissect/dissect.c
index c21d3e47e40af9a5a45e2ca9910731bb10dc311a..d70f1e791f607e71cfcc4cca8fcfa8bc52d369fd 100644 (file)
--- a/src/dissect/dissect.c
+++ b/src/dissect/dissect.c
@@ -781,6 +781,7 @@ static int run(int argc, char *argv[]) {
                         arg_image,
                         &arg_verity_settings,
                         NULL,
+                        d->uevent_seqnum_not_before,
                         arg_flags,
                         &m);
         if (r < 0)

diff --git a/src/gpt-auto-generator/gpt-auto-generator.c b/src/gpt-auto-generator/gpt-auto-generator.c
index 42549a2cd8c6785c864767433fc30376b175b2ff..eb80165bbee92581815880e7754d68268cddcb93 100644 (file)
--- a/src/gpt-auto-generator/gpt-auto-generator.c
+++ b/src/gpt-auto-generator/gpt-auto-generator.c
@@ -672,6 +672,7 @@ static int enumerate_partitions(dev_t devnum) {
         r = dissect_image(
                         fd,
                         NULL, NULL,
+                        UINT64_MAX,
                         DISSECT_IMAGE_GPT_ONLY|
                         DISSECT_IMAGE_NO_UDEV|
                         DISSECT_IMAGE_USR_NO_ROOT,

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 164a3302072cc5d575ee48beb32eb176533e83d5..070160241881360d0d1a636abe71e0655c394716 100644 (file)
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -5483,6 +5483,7 @@ static int run(int argc, char *argv[]) {
                                 arg_image,
                                 &arg_verity_settings,
                                 NULL,
+                                loop->uevent_seqnum_not_before,
                                 dissect_image_flags,
                                 &dissected_image);
                 if (r == -ENOPKG) {

diff --git a/src/portable/portable.c b/src/portable/portable.c
index e2bce279473c26a42d94db36b16f672156b44ab2..28d884a95139c1788e331a9eccc16327bb9941b6 100644 (file)
--- a/src/portable/portable.c
+++ b/src/portable/portable.c
@@ -395,6 +395,7 @@ static int portable_extract_by_path(
                 r = dissect_image(
                                 d->fd,
                                 NULL, NULL,
+                                d->uevent_seqnum_not_before,
                                 DISSECT_IMAGE_READ_ONLY |
                                 DISSECT_IMAGE_GENERIC_ROOT |
                                 DISSECT_IMAGE_REQUIRE_ROOT |

diff --git a/src/shared/discover-image.c b/src/shared/discover-image.c
index 43138e0a6f600437d1c6c484c2b050b7639f9a26..c343d089316e946d38dd2ea178e0fe3a1b0d89ee 100644 (file)
--- a/src/shared/discover-image.c
+++ b/src/shared/discover-image.c
@@ -1201,10 +1201,12 @@ int image_read_metadata(Image *i) {
                 r = dissect_image(
                                 d->fd,
                                 NULL, NULL,
+                                d->uevent_seqnum_not_before,
                                 DISSECT_IMAGE_GENERIC_ROOT |
                                 DISSECT_IMAGE_REQUIRE_ROOT |
                                 DISSECT_IMAGE_RELAX_VAR_CHECK |
-                                DISSECT_IMAGE_USR_NO_ROOT, &m);
+                                DISSECT_IMAGE_USR_NO_ROOT,
+                                &m);
                 if (r < 0)
                         return r;
 

diff --git a/src/shared/dissect-image.c b/src/shared/dissect-image.c
index f6971038def6b1982bca7a29cd692520b80dc683..345e1db9a7def9a089f7f96b678501dbed49bc78 100644 (file)
--- a/src/shared/dissect-image.c
+++ b/src/shared/dissect-image.c
@@ -260,6 +260,7 @@ struct wait_data {
         sd_device *parent_device;
         blkid_partition blkidp;
         sd_device *found;
+        uint64_t uevent_seqnum_not_before;
 };
 
 static inline void wait_data_done(struct wait_data *d) {
@@ -275,6 +276,20 @@ static int device_monitor_handler(sd_device_monitor *monitor, sd_device *device,
         if (device_for_action(device, SD_DEVICE_REMOVE))
                 return 0;
 
+        if (w->uevent_seqnum_not_before != UINT64_MAX) {
+                uint64_t seqnum;
+
+                r = sd_device_get_seqnum(device, &seqnum);
+                if (r < 0)
+                        goto finish;
+
+                if (seqnum <= w->uevent_seqnum_not_before) { /* From an older use of this loop device */
+                        log_debug("Dropping event because seqnum too old (%" PRIu64 " <= %" PRIu64 ")",
+                                  seqnum, w->uevent_seqnum_not_before);
+                        return 0;
+                }
+        }
+
         r = device_is_partition(device, w->parent_device, w->blkidp);
         if (r < 0)
                 goto finish;
@@ -294,6 +309,7 @@ static int wait_for_partition_device(
                 sd_device *parent,
                 blkid_partition pp,
                 usec_t deadline,
+                uint64_t uevent_seqnum_not_before,
                 sd_device **ret) {
 
         _cleanup_(sd_event_source_unrefp) sd_event_source *timeout_source = NULL;
@@ -336,6 +352,7 @@ static int wait_for_partition_device(
         _cleanup_(wait_data_done) struct wait_data w = {
                 .parent_device = parent,
                 .blkidp = pp,
+                .uevent_seqnum_not_before = uevent_seqnum_not_before,
         };
 
         r = sd_device_monitor_start(monitor, device_monitor_handler, &w);
@@ -492,6 +509,7 @@ int dissect_image(
                 int fd,
                 const VeritySettings *verity,
                 const MountOptions *mount_options,
+                uint64_t uevent_seqnum_not_before,
                 DissectImageFlags flags,
                 DissectedImage **ret) {
 
@@ -744,7 +762,7 @@ int dissect_image(
                 if (!pp)
                         return errno_or_else(EIO);
 
-                r = wait_for_partition_device(d, pp, deadline, &q);
+                r = wait_for_partition_device(d, pp, deadline, uevent_seqnum_not_before, &q);
                 if (r < 0)
                         return r;
 
@@ -2579,6 +2597,7 @@ int dissect_image_and_warn(
                 const char *name,
                 const VeritySettings *verity,
                 const MountOptions *mount_options,
+                uint64_t uevent_seqnum_not_before,
                 DissectImageFlags flags,
                 DissectedImage **ret) {
 
@@ -2593,7 +2612,7 @@ int dissect_image_and_warn(
                 name = buffer;
         }
 
-        r = dissect_image(fd, verity, mount_options, flags, ret);
+        r = dissect_image(fd, verity, mount_options, uevent_seqnum_not_before, flags, ret);
         switch (r) {
 
         case -EOPNOTSUPP:
@@ -2701,7 +2720,7 @@ int mount_image_privately_interactively(
         if (r < 0)
                 return log_error_errno(r, "Failed to set up loopback device: %m");
 
-        r = dissect_image_and_warn(d->fd, image, &verity, NULL, flags, &dissected_image);
+        r = dissect_image_and_warn(d->fd, image, &verity, NULL, d->uevent_seqnum_not_before, flags, &dissected_image);
         if (r < 0)
                 return r;
 
@@ -2792,6 +2811,7 @@ int verity_dissect_and_mount(
                         loop_device->fd,
                         &verity,
                         options,
+                        loop_device->uevent_seqnum_not_before,
                         dissect_image_flags,
                         &dissected_image);
         /* No partition table? Might be a single-filesystem image, try again */
@@ -2800,7 +2820,8 @@ int verity_dissect_and_mount(
                                 loop_device->fd,
                                 &verity,
                                 options,
-                                dissect_image_flags|DISSECT_IMAGE_NO_PARTITION_TABLE,
+                                loop_device->uevent_seqnum_not_before,
+                                dissect_image_flags | DISSECT_IMAGE_NO_PARTITION_TABLE,
                                 &dissected_image);
         if (r < 0)
                 return log_debug_errno(r, "Failed to dissect image: %m");

diff --git a/src/shared/dissect-image.h b/src/shared/dissect-image.h
index d51049e78a6fc9d0049f4aa158a40873c2bd5b1f..5d0b1d5e65eceb208dfc235725d400e2785d887e 100644 (file)
--- a/src/shared/dissect-image.h
+++ b/src/shared/dissect-image.h
@@ -159,8 +159,8 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(MountOptions*, mount_options_free_all);
 const char* mount_options_from_designator(const MountOptions *options, PartitionDesignator designator);
 
 int probe_filesystem(const char *node, char **ret_fstype);
-int dissect_image(int fd, const VeritySettings *verity, const MountOptions *mount_options, DissectImageFlags flags, DissectedImage **ret);
-int dissect_image_and_warn(int fd, const char *name, const VeritySettings *verity, const MountOptions *mount_options, DissectImageFlags flags, DissectedImage **ret);
+int dissect_image(int fd, const VeritySettings *verity, const MountOptions *mount_options, uint64_t uevent_seqnum_not_before, DissectImageFlags flags, DissectedImage **ret);
+int dissect_image_and_warn(int fd, const char *name, const VeritySettings *verity, const MountOptions *mount_options, uint64_t uevent_seqnum_not_before, DissectImageFlags flags, DissectedImage **ret);
 
 DissectedImage* dissected_image_unref(DissectedImage *m);
 DEFINE_TRIVIAL_CLEANUP_FUNC(DissectedImage*, dissected_image_unref);

diff --git a/src/sysext/sysext.c b/src/sysext/sysext.c
index 49ec23d93430637033a3b915eb2d8b028a8d7bd4..c305a30faef31696048aa2477b59cbb4347ac8bc 100644 (file)
--- a/src/sysext/sysext.c
+++ b/src/sysext/sysext.c
@@ -532,6 +532,7 @@ static int merge_subprocess(Hashmap *images, const char *workspace) {
                                         img->path,
                                         &verity_settings,
                                         NULL,
+                                        d->uevent_seqnum_not_before,
                                         flags,
                                         &m);
                         if (r < 0)

diff --git a/src/test/test-loop-block.c b/src/test/test-loop-block.c
index 93f2da70e77502537f28fbf8efc9e1c9c927129c..cfa999eff746ca41e0bf72869a6f5a21a4a307f0 100644 (file)
--- a/src/test/test-loop-block.c
+++ b/src/test/test-loop-block.c
@@ -51,7 +51,7 @@ static void* thread_func(void *ptr) {
 
                 log_notice("Acquired loop device %s, will mount on %s", loop->node, mounted);
 
-                r = dissect_image(loop->fd, NULL, NULL, DISSECT_IMAGE_READ_ONLY, &dissected);
+                r = dissect_image(loop->fd, NULL, NULL, loop->uevent_seqnum_not_before, DISSECT_IMAGE_READ_ONLY, &dissected);
                 if (r < 0)
                         log_error_errno(r, "Failed dissect loopback device %s: %m", loop->node);
                 assert_se(r >= 0);
@@ -188,7 +188,7 @@ int main(int argc, char *argv[]) {
         sfdisk = NULL;
 
         assert_se(loop_device_make(fd, O_RDWR, 0, UINT64_MAX, LO_FLAGS_PARTSCAN, &loop) >= 0);
-        assert_se(dissect_image(loop->fd, NULL, NULL, 0, &dissected) >= 0);
+        assert_se(dissect_image(loop->fd, NULL, NULL, loop->uevent_seqnum_not_before, 0, &dissected) >= 0);
 
         assert_se(dissected->partitions[PARTITION_ESP].found);
         assert_se(dissected->partitions[PARTITION_ESP].node);
@@ -212,7 +212,7 @@ int main(int argc, char *argv[]) {
         assert_se(make_filesystem(dissected->partitions[PARTITION_HOME].node, "ext4", "home", id, true) >= 0);
 
         dissected = dissected_image_unref(dissected);
-        assert_se(dissect_image(loop->fd, NULL, NULL, 0, &dissected) >= 0);
+        assert_se(dissect_image(loop->fd, NULL, NULL, loop->uevent_seqnum_not_before, 0, &dissected) >= 0);
 
         assert_se(mkdtemp_malloc(NULL, &mounted) >= 0);