volume_id: always check for all filesystem types and skip conflicting results

We probe for all known filesystems to find conflicting signatures. If
we find multiple matching signatures and one of the detected filesystem
types claims that it can not co-exist with any other filesystem type,
we do not return a probing result.

We can not afford to mount a volume with the wrong filesystem code and
possibly corrupt it. Linux ssytems have the problem of dozens of possible
filesystem types, and volumes with left-over signatures from former
filesystem types. Invalid signature need to be removed from the volume
to make the filesystem detection successful.

We do not want to read that many bytes from probed floppies, skip volumes
smaller than a usual floppy disk.

4 files changed, 52 insertions, 6 deletions

diff --git a/extras/volume_id/lib/fat.c b/extras/volume_id/lib/fat.c
index e30318cf09..2d98b65b50 100644
--- a/extras/volume_id/lib/fat.c
+++ b/extras/volume_id/lib/fat.c
@@ -497,6 +497,7 @@ fat32:
 found:
 	volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 	id->type = "vfat";
-
+	/* we think this is fat, but we make sure no other signatures are found */
+	id->force_unique_result = 1;
 	return 0;
 }
diff --git a/extras/volume_id/lib/libvolume_id-private.h b/extras/volume_id/lib/libvolume_id-private.h
index 14f7568fec..1b4a782b65 100644
--- a/extras/volume_id/lib/libvolume_id-private.h
+++ b/extras/volume_id/lib/libvolume_id-private.h
@@ -120,6 +120,7 @@ struct volume_id {
 	uint8_t		*seekbuf;
 	uint64_t	seekbuf_off;
 	size_t		seekbuf_len;
+	int		force_unique_result;
 };
 
 /* utils */
diff --git a/extras/volume_id/lib/linux_swap.c b/extras/volume_id/lib/linux_swap.c
index c4beeab978..1698e9dbf7 100644
--- a/extras/volume_id/lib/linux_swap.c
+++ b/extras/volume_id/lib/linux_swap.c
@@ -97,5 +97,7 @@ found_label:
 
 found:
 	volume_id_set_usage(id, VOLUME_ID_OTHER);
+	/* we think this is swap, but we make sure no other signatures are found */
+	id->force_unique_result = 1;
 	return 0;
 }
diff --git a/extras/volume_id/lib/volume_id.c b/extras/volume_id/lib/volume_id.c
index 8f22509ca6..e4d2ed4cfa 100644
--- a/extras/volume_id/lib/volume_id.c
+++ b/extras/volume_id/lib/volume_id.c
@@ -369,9 +369,12 @@ int volume_id_probe_raid(struct volume_id *id, uint64_t off, uint64_t size)
 
 	info("probing at offset 0x%" PRIx64 ", size 0x%" PRIx64 "\n", off, size);
 
-	for (i = 0; i < ARRAY_SIZE(prober_raid); i++)
-		if (prober_raid[i].prober(id, off, size) == 0)
+	for (i = 0; i < ARRAY_SIZE(prober_raid); i++) {
+		if (prober_raid[i].prober(id, off, size) == 0) {
+			info("signature '%s' detected\n", id->type);
 			goto found;
+		}
+	}
 	return -1;
 
 found:
@@ -402,11 +405,50 @@ int volume_id_probe_filesystem(struct volume_id *id, uint64_t off, uint64_t size
 
 	info("probing at offset 0x%" PRIx64 ", size 0x%" PRIx64 "\n", off, size);
 
-	for (i = 0; i < ARRAY_SIZE(prober_filesystem); i++)
-		if (prober_filesystem[i].prober(id, off, size) == 0)
+	/*
+	 * We probe for all known filesystems to find conflicting signatures. If
+	 * we find multiple matching signatures and one of the detected filesystem
+	 * types claims that it can not co-exist with any other filesystem type,
+	 * we do not return a probing result.
+	 *
+	 * We can not afford to mount a volume with the wrong filesystem code and
+	 * possibly corrupt it. Linux ssytems have the problem of dozens of possible
+	 * filesystem types, and volumes with left-over signatures from former
+	 * filesystem types. Invalid signature need to be removed from the volume
+	 * to make the filesystem detection successful.
+	 *
+	 * We do not want to read that many bytes from probed floppies, skip volumes
+	 * smaller than a usual floppy disk
+	 */
+	if (size > 1440 * 1024) {
+		int found = 0;
+		int force_unique_result = 0;
+
+		for (i = 0; i < ARRAY_SIZE(prober_filesystem); i++) {
+			int match;
+
+			match = (prober_filesystem[i].prober(id, off, size) == 0);
+			if (match) {
+				info("signature '%s' detected\n", id->type);
+				if (id->force_unique_result)
+					force_unique_result = id->force_unique_result;
+				if (found && force_unique_result) {
+					info("conflicting signatures found, skip results\n");
+					return -1;
+				}
+				found = 1;
+			}
+		}
+	}
+
+	/* return the first match */
+	for (i = 0; i < ARRAY_SIZE(prober_filesystem); i++) {
+		if (prober_filesystem[i].prober(id, off, size) == 0) {
+			info("signature '%s' detected\n", id->type);
 			goto found;
+		}
+	}
 	return -1;
-
 found:
 	/* If recognized, we free the allocated buffers */
 	volume_id_free_buffer(id);