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 <quwen...@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 <quwen...@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;

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