From daba5427dad6b260256053f914de2c0b79f7a79f Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Wed, 19 Feb 2014 15:39:16 +1100 Subject: [PATCH] xfs: skip verification on initial "guess" superblock read When xfs_readsb() does the very first read of the superblock, it makes a guess at the length of the buffer, based on the sector size of the underlying storage. This may or may not match the filesystem sector size in sb_sectsize, so we can't i.e. do a CRC check on it; it might be too short. In fact, mounting a filesystem with sb_sectsize larger than the device sector size will cause a mount failure if CRCs are enabled, because we are checksumming a length which exceeds the buffer passed to it. So always read twice; the first time we read with NULL buffer ops to skip verification; then set the proper read length, hook up the proper verifier, and give it another go. Once we are sure that we've got the right buffer length, we can also use bp->b_length in the xfs_sb_read_verify, rather than the less-trusted on-disk sectorsize for secondary superblocks. Before this we ran the risk of passing junk to the crc32c routines, which didn't always handle extreme values. Signed-off-by: Eric Sandeen Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- fs/xfs/xfs_mount.c | 24 ++++++++++++++++-------- fs/xfs/xfs_sb.c | 3 +-- 2 files changed, 17 insertions(+), 10 deletions(-) diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c index 02df7b408a26..f96c05669a9e 100644 --- a/fs/xfs/xfs_mount.c +++ b/fs/xfs/xfs_mount.c @@ -282,22 +282,29 @@ xfs_readsb( struct xfs_sb *sbp = &mp->m_sb; int error; int loud = !(flags & XFS_MFSI_QUIET); + const struct xfs_buf_ops *buf_ops; ASSERT(mp->m_sb_bp == NULL); ASSERT(mp->m_ddev_targp != NULL); + /* + * For the initial read, we must guess at the sector + * size based on the block device. It's enough to + * get the sb_sectsize out of the superblock and + * then reread with the proper length. + * We don't verify it yet, because it may not be complete. + */ + sector_size = xfs_getsize_buftarg(mp->m_ddev_targp); + buf_ops = NULL; + /* * Allocate a (locked) buffer to hold the superblock. * This will be kept around at all times to optimize * access to the superblock. */ - sector_size = xfs_getsize_buftarg(mp->m_ddev_targp); - reread: bp = xfs_buf_read_uncached(mp->m_ddev_targp, XFS_SB_DADDR, - BTOBB(sector_size), 0, - loud ? &xfs_sb_buf_ops - : &xfs_sb_quiet_buf_ops); + BTOBB(sector_size), 0, buf_ops); if (!bp) { if (loud) xfs_warn(mp, "SB buffer read failed"); @@ -328,12 +335,13 @@ reread: } /* - * If device sector size is smaller than the superblock size, - * re-read the superblock so the buffer is correctly sized. + * Re-read the superblock so the buffer is correctly sized, + * and properly verified. */ - if (sector_size < sbp->sb_sectsize) { + if (buf_ops == NULL) { xfs_buf_relse(bp); sector_size = sbp->sb_sectsize; + buf_ops = loud ? &xfs_sb_buf_ops : &xfs_sb_quiet_buf_ops; goto reread; } diff --git a/fs/xfs/xfs_sb.c b/fs/xfs/xfs_sb.c index 5071ccb67f07..359b19a4df42 100644 --- a/fs/xfs/xfs_sb.c +++ b/fs/xfs/xfs_sb.c @@ -611,7 +611,7 @@ xfs_sb_read_verify( XFS_SB_VERSION_5) || dsb->sb_crc != 0)) { - if (!xfs_verify_cksum(bp->b_addr, be16_to_cpu(dsb->sb_sectsize), + if (!xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length), offsetof(struct xfs_sb, sb_crc))) { /* Only fail bad secondaries on a known V5 filesystem */ if (bp->b_bn == XFS_SB_DADDR || @@ -644,7 +644,6 @@ xfs_sb_quiet_read_verify( { struct xfs_dsb *dsb = XFS_BUF_TO_SBP(bp); - if (dsb->sb_magicnum == cpu_to_be32(XFS_SB_MAGIC)) { /* XFS filesystem, verify noisily! */ xfs_sb_read_verify(bp); -- 2.30.2