[PATCH] btrfs-progs: Check superblock's checksum in btrfs-progs.

[PATCH] btrfs-progs: Check superblock's checksum in btrfs-progs.

[Qu Wenruo]

Btrfs-progs will read the superblock without checking the checksum.
When all superblocks are corrupted, continuing will cause disaster.

So this patch will add checksum check for btrfs-progs when reading
superblocks.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
---
 disk-io.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/disk-io.c b/disk-io.c
index 8db0335..3524834 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -990,7 +990,8 @@ int btrfs_scan_fs_devices(int fd, const char *path,
 	ret = btrfs_scan_one_device(fd, path, fs_devices,
 				    &total_devs, sb_bytenr);
 	if (ret) {
-		fprintf(stderr, "No valid Btrfs found on %s\n", path);
+		fprintf(stderr, "No valid Btrfs found or all superblock are corrupted on %s\n",
+			path);
 		return ret;
 	}
 
@@ -1100,7 +1101,7 @@ static struct btrfs_fs_info *__open_ctree_fd(int fp, const char *path,
 	else
 		ret = btrfs_read_dev_super(fp, disk_super, sb_bytenr);
 	if (ret) {
-		printk("No valid btrfs found\n");
+		fprintf(stderr, "No valid btrfs found or all super blocks are corrupted\n");
 		goto out_devices;
 	}
 
@@ -1191,6 +1192,8 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
 	int ret;
 	u64 transid = 0;
 	u64 bytenr;
+	u32 crc;
+	char crc_result[BTRFS_CSUM_SIZE];
 
 	if (sb_bytenr != BTRFS_SUPER_INFO_OFFSET) {
 		ret = pread64(fd, &buf, sizeof(buf), sb_bytenr);
@@ -1226,6 +1229,14 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
 		if (btrfs_super_magic(&buf) != BTRFS_MAGIC)
 			continue;
 
+		/* check if the superblock is damaged */
+		crc = ~(u32)0;
+		crc = btrfs_csum_data(NULL, (char *)sb + BTRFS_CSUM_SIZE,
+				      crc, BTRFS_SUPER_INFO_SIZE -
+				      BTRFS_CSUM_SIZE);
+		btrfs_csum_final(crc, crc_result);
+		if (memcmp(crc_result, sb->csum, BTRFS_CSUM_SIZE))
+			continue;
 		if (!fsid_is_initialized) {
 			memcpy(fsid, buf.fsid, sizeof(fsid));
 			fsid_is_initialized = 1;
-- 
2.0.0

Re: [PATCH] btrfs-progs: Check superblock's checksum in btrfs-progs.

[Qu Wenruo]

I'm very sorry that this patch breaks the open_ctree().
1) pread() only reads sizeof(struct btrfs_super_block), not 
BTRFS_SUPER_INFO_SIZE.
Which makes csum always dismatch.

2) memcpy() uses wrong src(should be 'buf' not 'sb').

I'll send v2 version patch soon.

Thanks,
Qu
-------- Original Message --------
Subject: [PATCH] btrfs-progs: Check superblock's checksum in btrfs-progs.
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: linux-btrfs@vger.kernel.org
Date: 2014年06月27日 10:34
> Btrfs-progs will read the superblock without checking the checksum.
> When all superblocks are corrupted, continuing will cause disaster.
>
> So this patch will add checksum check for btrfs-progs when reading
> superblocks.
>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
>   disk-io.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/disk-io.c b/disk-io.c
> index 8db0335..3524834 100644
> --- a/disk-io.c
> +++ b/disk-io.c
> @@ -990,7 +990,8 @@ int btrfs_scan_fs_devices(int fd, const char *path,
>   	ret = btrfs_scan_one_device(fd, path, fs_devices,
>   				    &total_devs, sb_bytenr);
>   	if (ret) {
> -		fprintf(stderr, "No valid Btrfs found on %s\n", path);
> +		fprintf(stderr, "No valid Btrfs found or all superblock are corrupted on %s\n",
> +			path);
>   		return ret;
>   	}
>   
> @@ -1100,7 +1101,7 @@ static struct btrfs_fs_info *__open_ctree_fd(int fp, const char *path,
>   	else
>   		ret = btrfs_read_dev_super(fp, disk_super, sb_bytenr);
>   	if (ret) {
> -		printk("No valid btrfs found\n");
> +		fprintf(stderr, "No valid btrfs found or all super blocks are corrupted\n");
>   		goto out_devices;
>   	}
>   
> @@ -1191,6 +1192,8 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
>   	int ret;
>   	u64 transid = 0;
>   	u64 bytenr;
> +	u32 crc;
> +	char crc_result[BTRFS_CSUM_SIZE];
>   
>   	if (sb_bytenr != BTRFS_SUPER_INFO_OFFSET) {
>   		ret = pread64(fd, &buf, sizeof(buf), sb_bytenr);
> @@ -1226,6 +1229,14 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
>   		if (btrfs_super_magic(&buf) != BTRFS_MAGIC)
>   			continue;
>   
> +		/* check if the superblock is damaged */
> +		crc = ~(u32)0;
> +		crc = btrfs_csum_data(NULL, (char *)sb + BTRFS_CSUM_SIZE,
> +				      crc, BTRFS_SUPER_INFO_SIZE -
> +				      BTRFS_CSUM_SIZE);
> +		btrfs_csum_final(crc, crc_result);
> +		if (memcmp(crc_result, sb->csum, BTRFS_CSUM_SIZE))
> +			continue;
>   		if (!fsid_is_initialized) {
>   			memcpy(fsid, buf.fsid, sizeof(fsid));
>   			fsid_is_initialized = 1;