From 7b26b3a6684c7737e889b0e93f57d14e726c5bab Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Thu, 16 May 2019 15:42:49 +0800 Subject: [PATCH] iomap: sub-block dio needs to zeroout beyond EOF mainline inclusion from mainline-4.20-rc4 commit b450672fb66b4a991a5b55ee24209ac7ae7690ce category: bugfix bugzilla: 15775 CVE: NA --------------------------- 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 Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: zhengbin Reviewed-by: Hou Tao Signed-off-by: Yang Yingliang --- fs/iomap.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/iomap.c b/fs/iomap.c index 914c07c9e0d6..d3d227682f7d 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -1700,7 +1700,14 @@ 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) -- GitLab