[PATCH-v2] erofs: code for verifying superblock checksum of an erofs image.

From: Pratik Shinde
Date: Tue Oct 22 2019 - 11:40:12 EST


Patch for kernel side changes of checksum feature.Used kernel's
crc32c library for calculating the checksum.

Signed-off-by: Pratik Shinde <pratikshinde320@xxxxxxxxx>
---
fs/erofs/erofs_fs.h | 5 +++--
fs/erofs/internal.h | 3 ++-
fs/erofs/super.c | 33 +++++++++++++++++++++++++++++++++
3 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index b1ee565..4d8097a 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -17,6 +17,7 @@
*/
#define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001
#define EROFS_ALL_FEATURE_INCOMPAT EROFS_FEATURE_INCOMPAT_LZ4_0PADDING
+#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001

/* 128-byte erofs on-disk super block */
struct erofs_super_block {
@@ -37,8 +38,8 @@ struct erofs_super_block {
__u8 uuid[16]; /* 128-bit uuid for volume */
__u8 volume_name[16]; /* volume name */
__le32 feature_incompat;
-
- __u8 reserved2[44];
+ __le32 chksum_blocks; /* number of blocks used for checksum */
+ __u8 reserved2[40];
};

/*
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 544a453..cec27ca 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -86,7 +86,7 @@ struct erofs_sb_info {
u8 uuid[16]; /* 128-bit uuid for volume */
u8 volume_name[16]; /* volume name */
u32 feature_incompat;
-
+ u32 feature_compat;
unsigned int mount_opt;
};

@@ -426,6 +426,7 @@ static inline void z_erofs_exit_zip_subsystem(void) {}
#endif /* !CONFIG_EROFS_FS_ZIP */

#define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */
+#define EFSBADCRC EBADMSG /* Bad crc found */

#endif /* __EROFS_INTERNAL_H */

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 0e36949..9cda72d 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 +47,31 @@ void _erofs_info(struct super_block *sb, const char *function,
va_end(args);
}

+static int erofs_validate_sb_chksum(struct erofs_super_block *dsb,
+ struct super_block *sb)
+{
+ u32 disk_chksum, nblocks, crc = 0;
+ void *kaddr;
+ struct page *page;
+ int i;
+
+ disk_chksum = le32_to_cpu(dsb->checksum);
+ nblocks = le32_to_cpu(dsb->chksum_blocks);
+ dsb->checksum = 0;
+ for (i = 0; i < nblocks; i++) {
+ page = erofs_get_meta_page(sb, i);
+ if (IS_ERR(page))
+ return PTR_ERR(page);
+ kaddr = kmap(page);
+ crc = crc32c(crc, kaddr, EROFS_BLKSIZ);
+ kunmap(page);
+ unlock_page(page);
+ }
+ if (crc != disk_chksum)
+ return -EFSBADCRC;
+ return 0;
+}
+
static void erofs_inode_init_once(void *ptr)
{
struct erofs_inode *vi = ptr;
@@ -121,6 +147,13 @@ static int erofs_read_superblock(struct super_block *sb)
goto out;
}

+ if (dsb->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) {
+ ret = erofs_validate_sb_chksum(dsb, sb);
+ if (ret < 0) {
+ erofs_err(sb, "super block checksum incorrect");
+ goto out;
+ }
+ }
blkszbits = dsb->blkszbits;
/* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */
if (blkszbits != LOG_BLOCK_SIZE) {
--
2.9.3