From: silentcreek <silentcreek@users.noreply.github.com>
Date: Sat, 4 Apr 2026 21:26:01 +0000 (+0000)
Subject: libblkid: Ignore secondary LUKS2 header in blkid_do_safeprobe()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3e60c1fe124dccd4e04d258ed7ff23f2d3ff4931;p=thirdparty%2Futil-linux.git

libblkid: Ignore secondary LUKS2 header in blkid_do_safeprobe()

The secondary LUKS2 header can match file data content on other
filesystems (e.g. an image file of a LUKS2 device stored on XFS whose
data blocks happen to land at device offsets where blkid looks for the
secondary LUKS2 header). This causes blkid to report a crypto_LUKS
superblock instead of the real filesystem.

Add a new flag BLKID_PROBE_FL_SAFEPROBE and skip scanning for the
secondary LUKS2 header in blkid_do_safeprobe(). The secondary LUKS2
header is only important for wipefs which uses a promiscuous probe.

Fixes: #4170
Fixes: 8bee1a2
Signed-off-by: Timo Sigurdsson <public_timo.s@silentcreek.de>

--
v2: Fix conflict with BLKID_FL_TINY_DEV flag
v3: Use pr->prob_flags instead of pr->flags
v4: Use original mask again as the use prob_flags resolves the conflict
---

diff --git a/libblkid/src/blkidP.h b/libblkid/src/blkidP.h
index f1bb3f8f5..dd4937fd0 100644
--- a/libblkid/src/blkidP.h
+++ b/libblkid/src/blkidP.h
@@ -245,6 +245,7 @@ struct blkid_struct_probe
 
 /* private per-probing flags */
 #define BLKID_PROBE_FL_IGNORE_PT (1 << 1)	/* ignore partition table */
+#define BLKID_PROBE_FL_SAFEPROBE (1 << 2)	/* safeprobe mode */
 
 extern blkid_probe blkid_clone_probe(blkid_probe parent);
 extern blkid_probe blkid_probe_get_wholedisk_probe(blkid_probe pr);
diff --git a/libblkid/src/probe.c b/libblkid/src/probe.c
index fba7eb124..0b0badc1e 100644
--- a/libblkid/src/probe.c
+++ b/libblkid/src/probe.c
@@ -1809,6 +1809,7 @@ int blkid_do_safeprobe(blkid_probe pr)
 		return BLKID_PROBE_NONE;
 
 	blkid_probe_start(pr);
+	pr->prob_flags |= BLKID_PROBE_FL_SAFEPROBE;
 
 	for (i = 0; i < BLKID_NCHAINS; i++) {
 		struct blkid_chain *chn;
diff --git a/libblkid/src/superblocks/luks.c b/libblkid/src/superblocks/luks.c
index 5ab7e73c9..e7e379c8d 100644
--- a/libblkid/src/superblocks/luks.c
+++ b/libblkid/src/superblocks/luks.c
@@ -126,16 +126,19 @@ static int probe_luks(blkid_probe pr, const struct blkid_idmag *mag __attribute_
 		return luks_attributes(pr, header, 0);
 	}
 
-	/* No primary header, scan for known offsets of LUKS2 secondary header. */
-	for (i = 0; i < ARRAY_SIZE(secondary_offsets); i++) {
-		header = (struct luks2_phdr *) blkid_probe_get_buffer(pr,
-			  secondary_offsets[i], sizeof(struct luks2_phdr));
 
-		if (!header)
-			return errno ? -errno : BLKID_PROBE_NONE;
+	/* No primary header, scan for known offsets of LUKS2 secondary header unless this is a safeprobe */
+	if (!(pr->prob_flags & BLKID_PROBE_FL_SAFEPROBE)) {
+		for (i = 0; i < ARRAY_SIZE(secondary_offsets); i++) {
+			header = (struct luks2_phdr *) blkid_probe_get_buffer(pr,
+				  secondary_offsets[i], sizeof(struct luks2_phdr));
 
-		if (luks_valid(header, LUKS_MAGIC_2, secondary_offsets[i]))
-			return luks_attributes(pr, header, secondary_offsets[i]);
+			if (!header)
+				return errno ? -errno : BLKID_PROBE_NONE;
+
+			if (luks_valid(header, LUKS_MAGIC_2, secondary_offsets[i]))
+				return luks_attributes(pr, header, secondary_offsets[i]);
+		}
 	}
 
 	return BLKID_PROBE_NONE;