On Tue, Mar 29, 2022 at 05:23:40PM +1100, Dave Chinner wrote: > On Tue, Mar 29, 2022 at 10:52:04AM +0530, Chandan Babu R wrote: > > On 25 Mar 2022 at 03:44, Dave Chinner wrote: > > > On Mon, Mar 21, 2022 at 10:47:46AM +0530, Chandan Babu R wrote: > > >> The maximum file size that can be represented by the data fork extent counter > > >> in the worst case occurs when all extents are 1 block in length and each block > > >> is 1KB in size. > > >> > > >> With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and with > > >> 1KB sized blocks, a file can reach upto, > > >> (2^31) * 1KB = 2TB > > >> > > >> This is much larger than the theoretical maximum size of a directory > > >> i.e. 32GB * 3 = 96GB. > > >> > > >> Since a directory's inode can never overflow its data fork extent counter, > > >> this commit replaces checking the return value of > > >> xfs_iext_count_may_overflow() with calls to ASSERT(error == 0). > > > > > > I'd really prefer that we don't add noise like this to a bunch of > > > call sites. If directories can't overflow the extent count in > > > normal operation, then why are we even calling > > > xfs_iext_count_may_overflow() in these paths? i.e. an overflow would > > > be a sign of an inode corruption, and we should have flagged that > > > long before we do an operation that might overflow the extent count. > > > > > > So, really, I think you should document the directory size > > > constraints at the site where we define all the large extent count > > > values in xfs_format.h, remove the xfs_iext_count_may_overflow() > > > checks from the directory code and replace them with a simple inode > > > verifier check that we haven't got more than 100GB worth of > > > individual extents in the data fork for directory inodes.... > > > > I don't think that we could trivially verify if the extents in a directory's > > data fork add up to more than 96GB. > > dip->di_nextents tells us how many extents there are in the data > fork, we know what the block size of the filesystem is, so it should > be pretty easy to calculate a maximum extent count for 96GB of > space. i.e. absolute maximum valid dir data fork extent count > is (96GB / blocksize). > > > > > xfs_dinode->di_size tracks the size of XFS_DIR2_DATA_SPACE. This also includes > > holes that could be created by freeing directory entries in a single directory > > block. Also, there is no easy method to determine the space occupied by > > XFS_DIR2_LEAF_SPACE and XFS_DIR2_FREE_SPACE segments of a directory. > > Sure there is. We do this sort of calc for things like transaction > reservations via definitions like XFS_DA_NODE_MAXDEPTH. That tells us Hmmm. Seeing as I just replaced XFS_BTREE_MAXLEVELS with dynamic limits set for each filesytem, is XFS_DA_NODE_MAXDEPTH even appropriate for modern filesystems? We're about to start allowing far more extended attributes in the form of parent pointers, so we should be careful about this. For a directory, there can be at most 32GB of directory entries, so the maximum number of directory entries is... 32GB / (directory block size) * (max entries per dir block) The dabtree stores (u32 hash, u32 offset) records, so I guess it wouldn't be so hard to compute the number of blocks needed for each node level until we only need one block, and that's our real XFS_DA_NODE_MAXEPTH. But then the second question is: what's the maximum height of a dabtree that indexes an xattr structure? I don't think there's any maximum limit within XFS on the number of attrs you can set on a file, is there? At least until you hit the iext_max_count check. I think the VFS institutes its own limit of 64k for the llistxattr buffer, but that's about all I can think of. I suppose right now the xattr structure can't grow larger than 2^(16+21) blocks in size, which is 2^49 bytes, but that's a mix of attr leaves and dabtree blocks, unlike directories, right? > immediately how many blocks can be in the XFS_DIR2_LEAF_SPACE > segement.... > > We also know the maximum number of individual directory blocks in > the 32GB segment (fixed at 32GB / dir block size), so the free space > array is also a fixed size at (32GB / dir block size / free space > entries per block). > > It's easy to just use (96GB / block size) and that will catch most > corruptions with no risk of a false positive detection, but we could > quite easily refine this to something like: > > data (32GB + > leaf btree blocks(XFS_DA_NODE_MAXDEPTH) + > freesp (32GB / free space records per block)) > frags / filesystem block size I think we ought to do a more careful study of XFS_DA_NODE_MAXDEPTH, but it could become more involved than we think. In the interest of keeping this series moving, can we start with a new verifier check that (di_nextents < that formula from above) and then refine that based on whatever improvements we may or may not come up with for XFS_DA_NODE_MAXDEPTH? > > > May be the following can be added to xfs_dinode_verify(), > > > > if (S_ISDIR(mode) && ((xfs_dinode->di_size + 2 * 32GB) > 96GB)) > > return __this_address > > That doesn't validate that the on disk or in-memory di_nextents > value is withing the known valid range or not. We can do that > directly (as per above), so we shouldn't need a hueristic like this. Indeed, inode size is not a good proxy variable for extent count. > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
