btrfs-progs: Check sb_bytenr with device size before scanning one device.

When using btrfs check with -s option, if using '-s 2' on a small
device which doesn't have the third superblock, "No valid Btrfs found"
will be output, but it is not appropriate.

So check sb_bytenr against device size before scanning a device and
output proper error message.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

diff --git a/disk-io.c b/disk-io.c
index e22122c..03edf8e 100644 (file)
--- a/disk-io.c
+++ b/disk-io.c
@@ -1008,10 +1008,20 @@ int btrfs_scan_fs_devices(int fd, const char *path,
                          u64 sb_bytenr, int super_recover)
 {
        u64 total_devs;
+       u64 dev_size;
        int ret;
        if (!sb_bytenr)
                sb_bytenr = BTRFS_SUPER_INFO_OFFSET;
 
+       dev_size = lseek(fd, 0, SEEK_END);
+       if (dev_size < 0)
+               return (int)(dev_size);
+       lseek(fd, 0, SEEK_SET);
+       if (sb_bytenr > dev_size) {
+               fprintf(stderr, "Superblock bytenr is larger than device size\n");
+               return -EINVAL;
+       }
+
        ret = btrfs_scan_one_device(fd, path, fs_devices,
                                    &total_devs, sb_bytenr, super_recover);
        if (ret) {