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iomap: sub-block dio needs to zeroout beyond EOF 

If we are doing sub-block dio that extends EOF, we need to zero
the unused tail of the block to initialise the data in it it. If we
do not zero the tail of the block, then an immediate mmap read of
the EOF block will expose stale data beyond EOF to userspace. Found
with fsx running sub-block DIO sizes vs MAPREAD/MAPWRITE operations.

Fix this by detecting if the end of the DIO write is beyond EOF
and zeroing the tail if necessary.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Dave Chinner 2018-11-19 13:31:10 -08:00 committed by Darrick J. Wong
parent 0929d85800
commit b450672fb6
1 changed files with 8 additions and 1 deletions
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9
fs/iomap.c
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@ -1677,7 +1677,14 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
dio->submit.cookie = submit_bio(bio);
} while (nr_pages);
if (need_zeroout) {
/*
* We need to zeroout the tail of a sub-block write if the extent type
* requires zeroing or the write extends beyond EOF. If we don't zero
* the block tail in the latter case, we can expose stale data via mmap
* reads of the EOF block.
*/
if (need_zeroout ||
((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
/* zero out from the end of the write to the end of the block */
pad = pos & (fs_block_size - 1);
if (pad)