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>

1 files changed, 10 insertions, 0 deletions

diff --git a/disk-io.c b/disk-io.c
index e22122c..03edf8e 100644
--- 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) {