[WIP PATCH 1/4] udf: Do not access LVIDIU revision members when they are not filled

["Pali Rohár" <pali.rohar@gmail.com>]

minUDFReadRev, minUDFWriteRev and maxUDFWriteRev members were introduced in
UDF 1.02. Previous UDF revisions used that area for implementation specific
data. So in this case do not touch these members.

To check if LVIDIU contain revisions members, first read UDF revision from
LVD. If revision is at least 1.02 LVIDIU should contain revision members.

This change should fix mounting UDF 1.01 images in R/W mode. Kernel would
not touch, read overwrite implementation specific area of LVIDIU.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
---
 fs/udf/super.c  | 37 ++++++++++++++++++++++++++-----------
 fs/udf/udf_sb.h |  3 +++
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/fs/udf/super.c b/fs/udf/super.c
index 2d0b90800..8df6e9962 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -765,7 +765,7 @@ static int udf_check_vsd(struct super_block *sb)
 }
 
 static int udf_verify_domain_identifier(struct super_block *sb,
-					struct regid *ident, char *dname)
+					struct regid *ident, char *dname, u16 *udf_rev)
 {
 	struct domainIdentSuffix *suffix;
 
@@ -779,6 +779,8 @@ static int udf_verify_domain_identifier(struct super_block *sb,
 		goto force_ro;
 	}
 	suffix = (struct domainIdentSuffix *)ident->identSuffix;
+	if (udf_rev)
+		*udf_rev = le16_to_cpu(suffix->UDFRevision);
 	if ((suffix->domainFlags & DOMAIN_FLAGS_HARD_WRITE_PROTECT) ||
 	    (suffix->domainFlags & DOMAIN_FLAGS_SOFT_WRITE_PROTECT)) {
 		if (!sb_rdonly(sb)) {
@@ -801,7 +803,7 @@ static int udf_load_fileset(struct super_block *sb, struct fileSetDesc *fset,
 {
 	int ret;
 
-	ret = udf_verify_domain_identifier(sb, &fset->domainIdent, "file set");
+	ret = udf_verify_domain_identifier(sb, &fset->domainIdent, "file set", NULL);
 	if (ret < 0)
 		return ret;
 
@@ -1404,7 +1406,7 @@ static int udf_load_logicalvol(struct super_block *sb, sector_t block,
 	}
 
 	ret = udf_verify_domain_identifier(sb, &lvd->domainIdent,
-					   "logical volume");
+					   "logical volume", &sbi->s_lvd_udfrev);
 	if (ret)
 		goto out_bh;
 	ret = udf_sb_alloc_partition_maps(sb, le32_to_cpu(lvd->numPartitionMaps));
@@ -2055,12 +2057,19 @@ static void udf_close_lvid(struct super_block *sb)
 	mutex_lock(&sbi->s_alloc_mutex);
 	lvidiu->impIdent.identSuffix[0] = UDF_OS_CLASS_UNIX;
 	lvidiu->impIdent.identSuffix[1] = UDF_OS_ID_LINUX;
-	if (UDF_MAX_WRITE_VERSION > le16_to_cpu(lvidiu->maxUDFWriteRev))
-		lvidiu->maxUDFWriteRev = cpu_to_le16(UDF_MAX_WRITE_VERSION);
-	if (sbi->s_udfrev > le16_to_cpu(lvidiu->minUDFReadRev))
-		lvidiu->minUDFReadRev = cpu_to_le16(sbi->s_udfrev);
-	if (sbi->s_udfrev > le16_to_cpu(lvidiu->minUDFWriteRev))
-		lvidiu->minUDFWriteRev = cpu_to_le16(sbi->s_udfrev);
+
+	/* minUDFReadRev, minUDFWriteRev and maxUDFWriteRev members were
+	 * introduced in UDF 1.02. Previous UDF revisions used that area for
+	 * implementation specific data. So in this case do not touch it. */
+	if (sbi->s_lvd_udfrev >= 0x0102) {
+		if (UDF_MAX_WRITE_VERSION > le16_to_cpu(lvidiu->maxUDFWriteRev))
+			lvidiu->maxUDFWriteRev = cpu_to_le16(UDF_MAX_WRITE_VERSION);
+		if (sbi->s_udfrev > le16_to_cpu(lvidiu->minUDFReadRev))
+			lvidiu->minUDFReadRev = cpu_to_le16(sbi->s_udfrev);
+		if (sbi->s_udfrev > le16_to_cpu(lvidiu->minUDFWriteRev))
+			lvidiu->minUDFWriteRev = cpu_to_le16(sbi->s_udfrev);
+	}
+
 	if (!UDF_QUERY_FLAG(sb, UDF_FLAG_INCONSISTENT))
 		lvid->integrityType = cpu_to_le32(LVID_INTEGRITY_TYPE_CLOSE);
 
@@ -2220,8 +2229,14 @@ static int udf_fill_super(struct super_block *sb, void *options, int silent)
 			ret = -EINVAL;
 			goto error_out;
 		}
-		minUDFReadRev = le16_to_cpu(lvidiu->minUDFReadRev);
-		minUDFWriteRev = le16_to_cpu(lvidiu->minUDFWriteRev);
+
+		if (sbi->s_lvd_udfrev >= 0x0102) { /* minUDFReadRev and minUDFWriteRev were introduced in UDF 1.02 */
+			minUDFReadRev = le16_to_cpu(lvidiu->minUDFReadRev);
+			minUDFWriteRev = le16_to_cpu(lvidiu->minUDFWriteRev);
+		} else {
+			minUDFReadRev = minUDFWriteRev = sbi->s_lvd_udfrev;
+		}
+
 		if (minUDFReadRev > UDF_MAX_READ_VERSION) {
 			udf_err(sb, "minUDFReadRev=%x (max is %x)\n",
 				minUDFReadRev,
diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h
index 3d83be54c..6bd0d4430 100644
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -137,6 +137,9 @@ struct udf_sb_info {
 	/* Fileset Info */
 	__u16			s_serial_number;
 
+	/* LVD UDF revision filled to media at format time */
+	__u16			s_lvd_udfrev;
+
 	/* highest UDF revision we have recorded to this media */
 	__u16			s_udfrev;
 
-- 
2.20.1