[U-Boot] [PATCH 1/1] ext4: Refuse to mount filesystems with 64bit feature set

[Tom Rini]

With e2fsprogs after 1.43 the 64bit and metadata_csum features are
enabled by default.  The metadata_csum feature changes how
ext4_group_desc->bg_checksum is calculated, which would break write
support.  The 64bit feature however introduces changes such that it
cannot be read by implementations that do not support it.  Since we do
not support this, we must not mount it.

Cc: Stephen Warren <swarren at nvidia.com>
Cc: Simon Glass <sjg at chromium.org>
Cc: Lukasz Majewski <l.majewski at samsung.com>
Cc: Stefan Roese <sr at denx.de>
Reported-by: Andrew Bradford <andrew.bradford at kodakalaris.com>
Signed-off-by: Tom Rini <trini at konsulko.com>
---
This problem has been seen in the wild a few times and reported in many
places.  If you've also found this problem, and reported it, please feel
free to reply with a Reported-by tag, patchwork will pick them up.
Further, we should look at adding support for 64bit and metadata_csum
features as they will be showing up a lot more often now, but that's
also non-trivial.  A graceful fail like this is better than users being
unable to load their files and being very puzzled.
---
 fs/ext4/ext4_common.c | 10 ++++++++++
 include/ext4fs.h      |  1 +
 2 files changed, 11 insertions(+)

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 40b798a..eb49fce 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -2229,6 +2229,16 @@ int ext4fs_mount(unsigned part_length)
 	if (__le16_to_cpu(data->sblock.magic) != EXT2_MAGIC)
 		goto fail;
 
+	/*
+	 * The 64bit feature was enabled when metadata_csum was enabled
+	 * and we do not support metadata_csum (and cannot reliably find
+	 * files when it is set.  Refuse to mount.
+	 */
+	if (data->sblock.feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) {
+		printf("Unsupported feature found (64bit, possibly metadata_csum), not mounting\n");
+		goto fail;
+	}
+
 	if (__le32_to_cpu(data->sblock.revision_level == 0))
 		fs->inodesz = 128;
 	else
diff --git a/include/ext4fs.h b/include/ext4fs.h
index cc765ae..13d2c56 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -32,6 +32,7 @@
 #define EXT4_EXT_MAGIC			0xf30a
 #define EXT4_FEATURE_RO_COMPAT_GDT_CSUM	0x0010
 #define EXT4_FEATURE_INCOMPAT_EXTENTS	0x0040
+#define EXT4_FEATURE_INCOMPAT_64BIT	0x0080
 #define EXT4_INDIRECT_BLOCKS		12
 
 #define EXT4_BG_INODE_UNINIT		0x0001
-- 
2.7.4