From: Dave Chinner <dchinner@xxxxxxxxxx>
If we are soing 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@xxxxxxxxxx>
---
fs/iomap.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/iomap.c b/fs/iomap.c
index 64ce240217a1..16d16596b00f 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1676,7 +1676,14 @@ 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 th 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)
--
2.19.1
