xfs: disallow rw remount on fs with unknown ro-compat features
PATCH 1/1 xfs: disallow rw remount on fs with unknown ro-compat features
Today, a kernel which refuses to mount a filesystem read-write due to unknown ro-compat features can still transition to read-write via the remount path. The old kernel is most likely none the wiser, because it's unaware of the new feature, and isn't using it. However, writing to the filesystem may well corrupt metadata related to that new feature, and moving to a newer kernel which understand the feature will have problems.
Right now the only ro-compat feature we have is the free inode btree, which showed up in v3.16. It would be good to push this back to all the active stable kernels, I think, so that if anyone is using newer mkfs (which enables the finobt feature) with older kernel releases, they'll be protected.
---
fs/xfs/xfs_super.c +10 -0
@@ -1276,6 +1276,16 @@ xfs_fs_remount(return -EINVAL ; } +if (XFS_SB_VERSION_NUM (sbp) ==XFS_SB_VERSION_5 && +xfs_sb_has_ro_compat_feature (sbp, +XFS_SB_FEAT_RO_COMPAT_UNKNOWN )) { +xfs_warn (mp, +"ro->rw transition prohibited on unknown (0x%x) ro-compat filesystem" , + (sbp->sb_features_ro_compat & +XFS_SB_FEAT_RO_COMPAT_UNKNOWN )); +return -EINVAL ; + } + mp->m_flags &= ~XFS_MOUNT_RDONLY ;/*
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Quoted 14 lines · Eric Sandeen
Today, a kernel which refuses to mount a filesystem read-write due to unknown ro-compat features can still transition to read-write via the remount path. The old kernel is most likely none the wiser, because it's unaware of the new feature, and isn't using it. However, writing to the filesystem may well corrupt metadata related to that new feature, and moving to a newer kernel which understand the feature will have problems.
Right now the only ro-compat feature we have is the free inode btree, which showed up in v3.16. It would be good to push this back to all the active stable kernels, I think, so that if anyone is using newer mkfs (which enables the finobt feature) with older kernel releases, they'll be protected.
Quoted 3 lines
Signed-off-by Eric Sandeen <[email protected]>---
Quoted 23 lines
fs/xfs/xfs_super.c +10
-0@@ -1276,6 +1276,16 @@ xfs_fs_remount(return -EINVAL ; } +if (XFS_SB_VERSION_NUM (sbp) ==XFS_SB_VERSION_5 && +xfs_sb_has_ro_compat_feature (sbp, +XFS_SB_FEAT_RO_COMPAT_UNKNOWN )) { +xfs_warn (mp, +"ro->rw transition prohibited on unknown (0x%x) ro-compat filesystem" , + (sbp->sb_features_ro_compat & +XFS_SB_FEAT_RO_COMPAT_UNKNOWN )); +return -EINVAL ; + } + mp->m_flags &= ~XFS_MOUNT_RDONLY ;/*
Quoted 4 lines
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Quoted 8 lines · Eric Sandeen
Today, a kernel which refuses to mount a filesystem read-write due to unknown ro-compat features can still transition to read-write via the remount path. The old kernel is most likely none the wiser, because it's unaware of the new feature, and isn't using it. However, writing to the filesystem may well corrupt metadata related to that new feature, and moving to a newer kernel which understand the feature will have problems.
Quoted 5 lines
Right now the only ro-compat feature we have is the free inode btree, which showed up in v3.16. It would be good to push this back to all the active stable kernels, I think, so that if anyone is using newer mkfs (which enables the finobt feature) with older kernel releases, they'll be protected.
Ok, so the bug was introduced with the original extended feature masks in commit e721f50 ("xfs: implement extended feature masks"), which was introduced in 3.10. So it will need to go back to stable kernels all the way back to 3.10, right?
Cheers,
Dave.
Signature · 7 lines
Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Quoted 15 lines · Dave Chinner
Quoted 8 lines · Eric Sandeen
Today, a kernel which refuses to mount a filesystem read-write due to unknown ro-compat features can still transition to read-write via the remount path. The old kernel is most likely none the wiser, because it's unaware of the new feature, and isn't using it. However, writing to the filesystem may well corrupt metadata related to that new feature, and moving to a newer kernel which understand the feature will have problems.
Quoted 5 lines
Right now the only ro-compat feature we have is the free inode btree, which showed up in v3.16. It would be good to push this back to all the active stable kernels, I think, so that if anyone is using newer mkfs (which enables the finobt feature) with older kernel releases, they'll be protected.
Quoted 9 lines
Ok, so the bug was introduced with the original extended feature masks in commit e721f50 ("xfs: implement extended feature masks"), which was introduced in 3.10. So it will need to go back to stable kernels all the way back to 3.10, right?
Cheers,
Dave.
Yeah, that seems right; it's not when the first ro-compat feature was introduced, it was when the handling was introduced, right?
If you need to massage the cc:stable line feel free, of course.
ie:
Cc: <[email protected]> # 3.10.x-
I think.
-Eric
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