This is a note to let you know that I've just added the patch titled
iomap: fix WARN_ON_ONCE() from unprivileged users
to the 5.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
iomap-fix-warn_on_once-from-unprivileged-users.patch
and it can be found in the queue-5.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f4f11e409c95b954e9e1fcca0e24a1211c73e702
Author: Qian Cai <cai@xxxxxx>
Date: Thu Sep 10 08:26:15 2020 -0700
iomap: fix WARN_ON_ONCE() from unprivileged users
[ Upstream commit a805c111650cdba6ee880f528abdd03c1af82089 ]
It is trivial to trigger a WARN_ON_ONCE(1) in iomap_dio_actor() by
unprivileged users which would taint the kernel, or worse - panic if
panic_on_warn or panic_on_taint is set. Hence, just convert it to
pr_warn_ratelimited() to let users know their workloads are racing.
Thank Dave Chinner for the initial analysis of the racing reproducers.
Signed-off-by: Qian Cai <cai@xxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index ec7b78e6fecaf..28d656b15300b 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -387,6 +387,16 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
return iomap_dio_bio_actor(inode, pos, length, dio, iomap);
case IOMAP_INLINE:
return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
+ case IOMAP_DELALLOC:
+ /*
+ * DIO is not serialised against mmap() access at all, and so
+ * if the page_mkwrite occurs between the writeback and the
+ * iomap_apply() call in the DIO path, then it will see the
+ * DELALLOC block that the page-mkwrite allocated.
+ */
+ pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n",
+ dio->iocb->ki_filp, current->comm);
+ return -EIO;
default:
WARN_ON_ONCE(1);
return -EIO;
