[PATCH 4.19 039/205] udf: Prevent write-unsupported filesystem to be remounted read-write

Greg Kroah-Hartman
2018-11-19T16:31:49Z

From: Jan Kara <jack@suse.cz>

[ Upstream commit a9ad01bc759df79b0012f43ee52164391e31cd96 ]

There are certain filesystem features which we support for reading but
not for writing. We properly refuse to mount such filesystems read-write
however for some features (such as read-only partitions), we don't check
for these features when remounting the filesystem from read-only to
read-write. Thus such filesystems could be remounted read-write leading
to strange behavior (most likely crashes).

Fix the problem by marking in superblock whether the filesystem has some
features that are supported in read-only mode and check this flag during
remount.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/udf/super.c | 30 ++++++++++++++++--------------
fs/udf/udf_sb.h | 2 ++
2 files changed, 18 insertions(+), 14 deletions(-)

--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -613,14 +613,11 @@ static int udf_remount_fs(struct super_b
struct udf_options uopt;
struct udf_sb_info *sbi = UDF_SB(sb);
int error = 0;
- struct logicalVolIntegrityDescImpUse *lvidiu = udf_sb_lvidiu(sb);
+
+ if (!(*flags & SB_RDONLY) && UDF_QUERY_FLAG(sb, UDF_FLAG_RW_INCOMPAT))
+ return -EACCES;

sync_filesystem(sb);
- if (lvidiu) {
- int write_rev = le16_to_cpu(lvidiu->minUDFWriteRev);
- if (write_rev > UDF_MAX_WRITE_VERSION && !(*flags & SB_RDONLY))
- return -EACCES;
- }

uopt.flags = sbi->s_flags;
uopt.uid = sbi->s_uid;
@@ -1257,6 +1254,7 @@ static int udf_load_partdesc(struct supe
ret = -EACCES;
goto out_bh;
}
+ UDF_SET_FLAG(sb, UDF_FLAG_RW_INCOMPAT);
ret = udf_load_vat(sb, i, type1_idx);
if (ret < 0)
goto out_bh;
@@ -2155,10 +2153,12 @@ static int udf_fill_super(struct super_b
UDF_MAX_READ_VERSION);
ret = -EINVAL;
goto error_out;
- } else if (minUDFWriteRev > UDF_MAX_WRITE_VERSION &&
- !sb_rdonly(sb)) {
- ret = -EACCES;
- goto error_out;
+ } else if (minUDFWriteRev > UDF_MAX_WRITE_VERSION) {
+ if (!sb_rdonly(sb)) {
+ ret = -EACCES;
+ goto error_out;
+ }
+ UDF_SET_FLAG(sb, UDF_FLAG_RW_INCOMPAT);
}

sbi->s_udfrev = minUDFWriteRev;
@@ -2176,10 +2176,12 @@ static int udf_fill_super(struct super_b
}

if (sbi->s_partmaps[sbi->s_partition].s_partition_flags &
- UDF_PART_FLAG_READ_ONLY &&
- !sb_rdonly(sb)) {
- ret = -EACCES;
- goto error_out;
+ UDF_PART_FLAG_READ_ONLY) {
+ if (!sb_rdonly(sb)) {
+ ret = -EACCES;
+ goto error_out;
+ }
+ UDF_SET_FLAG(sb, UDF_FLAG_RW_INCOMPAT);
}

if (udf_find_fileset(sb, &fileset, &rootdir)) {
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -30,6 +30,8 @@
#define UDF_FLAG_LASTBLOCK_SET 16
#define UDF_FLAG_BLOCKSIZE_SET 17
#define UDF_FLAG_INCONSISTENT 18
+#define UDF_FLAG_RW_INCOMPAT 19 /* Set when we find RW incompatible
+ * feature */

#define UDF_PART_FLAG_UNALLOC_BITMAP 0x0001
#define UDF_PART_FLAG_UNALLOC_TABLE 0x0002