iomap: sub-block dio needs to zeroout beyond EOF

BugLink: https://bugs.launchpad.net/bugs/1857158
[ Upstream commit b450672fb66b4a991a5b55ee24209ac7ae7690ce ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/fs/iomap.c b/fs/iomap.c
index 27e5b669bf7608fc926a8d86e706d78b1ce1c1a2..f99c7b6a7f9eeff2c8aa2999f96ef293f4ef649a 100644 (file)
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -950,7 +950,14 @@ iomap_dio_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)