There are some backward incompatible optimizations pending
for months, mainly due to on-disk format expensions.
However, we should ensure that it cannot be mounted with
old kernels. Otherwise, it will causes unexpected behaviors.
Fixes: ba2b77a82022 ("staging: erofs: add super block operations")
Cc: <stable@xxxxxxxxxxxxxxx> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
drivers/staging/erofs/erofs_fs.h | 11 +++++++++--
drivers/staging/erofs/super.c | 8 ++++++++
2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
index fa52898df006..531821757845 100644
--- a/drivers/staging/erofs/erofs_fs.h
+++ b/drivers/staging/erofs/erofs_fs.h
@@ -17,10 +17,16 @@
#define EROFS_SUPER_MAGIC_V1 0xE0F5E1E2
#define EROFS_SUPER_OFFSET 1024
+/*
+ * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
+ * incompatible with this kernel version.
+ */
+#define EROFS_ALL_REQUIREMENTS 0
+
struct erofs_super_block {
/* 0 */__le32 magic; /* in the little endian */
/* 4 */__le32 checksum; /* crc32c(super_block) */
-/* 8 */__le32 features;
+/* 8 */__le32 features; /* extra features for the image */
/* 12 */__u8 blkszbits; /* support block_size == PAGE_SIZE only */
/* 13 */__u8 reserved;
@@ -34,8 +40,9 @@ struct erofs_super_block {
/* 44 */__le32 xattr_blkaddr;
/* 48 */__u8 uuid[16]; /* 128-bit uuid for volume */
/* 64 */__u8 volume_name[16]; /* volume name */
+/* 80 */__le32 requirements; /* all mandatory minimum requirements */
-/* 80 */__u8 reserved2[48]; /* 128 bytes */
+/* 84 */__u8 reserved2[44]; /* 128 bytes */
} __packed;
/*
diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index f580d4ef77a1..815e5825db59 100644
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -104,6 +104,14 @@ static int superblock_read(struct super_block *sb)
goto out;
}
+ /* check if the kernel meets all mandatory requirements */
+ if (le32_to_cpu(layout->requirements) & (~EROFS_ALL_REQUIREMENTS)) {
+ errln("too old to meet minimum requirements: %x supported: %x",
+ le32_to_cpu(layout->requirements),
+ EROFS_ALL_REQUIREMENTS);
+ goto out;
+ }
+
sbi->blocks = le32_to_cpu(layout->blocks);
sbi->meta_blkaddr = le32_to_cpu(layout->meta_blkaddr);
#ifdef CONFIG_EROFS_FS_XATTR
--
2.17.1
