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Subject[PATCH v7] erofs: support superblock checksum
Date
From: Pratik Shinde <pratikshinde320@gmail.com>

Introduce superblock checksum feature in order to
check at mounting time.

Note that the first 1024 bytes are ignore for x86
boot sectors and other oddities.

Link: https://lore.kernel.org/r/20191030050846.175623-1-gaoxiang25@huawei.com
Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
changes since v6:
- fix kunmap(data) to kunmap(page) by mistake
reported by Dan Carpenter;

fs/erofs/Kconfig | 1 +
fs/erofs/erofs_fs.h | 3 ++-
fs/erofs/internal.h | 1 +
fs/erofs/super.c | 36 ++++++++++++++++++++++++++++++++++--
4 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 9d634d3a1845..74b0aaa7114c 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -3,6 +3,7 @@
config EROFS_FS
tristate "EROFS filesystem support"
depends on BLOCK
+ select LIBCRC32C
help
EROFS (Enhanced Read-Only File System) is a lightweight
read-only file system with modern designs (eg. page-sized
diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index b1ee5654750d..385fa49c7749 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -11,6 +11,8 @@

#define EROFS_SUPER_OFFSET 1024

+#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001
+
/*
* Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
* be incompatible with this kernel version.
@@ -37,7 +39,6 @@ struct erofs_super_block {
__u8 uuid[16]; /* 128-bit uuid for volume */
__u8 volume_name[16]; /* volume name */
__le32 feature_incompat;
-
__u8 reserved2[44];
};

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 544a453f3076..96d97eab88e3 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -85,6 +85,7 @@ struct erofs_sb_info {

u8 uuid[16]; /* 128-bit uuid for volume */
u8 volume_name[16]; /* volume name */
+ u32 feature_compat;
u32 feature_incompat;

unsigned int mount_opt;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 0e369494f2f2..849c0bdf49d9 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -9,6 +9,7 @@
#include <linux/statfs.h>
#include <linux/parser.h>
#include <linux/seq_file.h>
+#include <linux/crc32c.h>
#include "xattr.h"

#define CREATE_TRACE_POINTS
@@ -46,6 +47,30 @@ void _erofs_info(struct super_block *sb, const char *function,
va_end(args);
}

+static int erofs_superblock_csum_verify(struct super_block *sb, void *sbdata)
+{
+ struct erofs_super_block *dsb;
+ u32 expected_crc, crc;
+
+ dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET,
+ EROFS_BLKSIZ - EROFS_SUPER_OFFSET, GFP_KERNEL);
+ if (!dsb)
+ return -ENOMEM;
+
+ expected_crc = le32_to_cpu(dsb->checksum);
+ dsb->checksum = 0;
+ /* to allow for x86 boot sectors and other oddities. */
+ crc = crc32c(~0, dsb, EROFS_BLKSIZ - EROFS_SUPER_OFFSET);
+ kfree(dsb);
+
+ if (crc != expected_crc) {
+ erofs_err(sb, "invalid checksum 0x%08x, 0x%08x expected",
+ crc, expected_crc);
+ return -EBADMSG;
+ }
+ return 0;
+}
+
static void erofs_inode_init_once(void *ptr)
{
struct erofs_inode *vi = ptr;
@@ -112,7 +137,7 @@ static int erofs_read_superblock(struct super_block *sb)

sbi = EROFS_SB(sb);

- data = kmap_atomic(page);
+ data = kmap(page);
dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);

ret = -EINVAL;
@@ -121,6 +146,13 @@ static int erofs_read_superblock(struct super_block *sb)
goto out;
}

+ sbi->feature_compat = le32_to_cpu(dsb->feature_compat);
+ if (sbi->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) {
+ ret = erofs_superblock_csum_verify(sb, data);
+ if (ret)
+ goto out;
+ }
+
blkszbits = dsb->blkszbits;
/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
if (blkszbits != LOG_BLOCK_SIZE) {
@@ -155,7 +187,7 @@ static int erofs_read_superblock(struct super_block *sb)
}
ret = 0;
out:
- kunmap_atomic(data);
+ kunmap(page);
put_page(page);
return ret;
}
--
2.17.1
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