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 <[email protected]>
---
v3: Keep the default case and update the message.
v2: Record the path, pid and command as well.
fs/iomap/direct-io.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index c1aafb2ab990..b7f3311569bd 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -374,6 +374,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
void *data, struct iomap *iomap, struct iomap *srcmap)
{
struct iomap_dio *dio = data;
+ char pathname[128], *path;
switch (iomap->type) {
case IOMAP_HOLE:
@@ -388,6 +389,21 @@ 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.
+ */
+ path = file_path(dio->iocb->ki_filp, pathname,
+ sizeof(pathname));
+ if (IS_ERR(path))
+ path = "(unknown)";
+
+ pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %s Comm: %.20s\n",
+ path, current->comm);
+ return -EIO;
default:
WARN_ON_ONCE(1);
return -EIO;
--
2.18.4
On Mon, Aug 31, 2020 at 01:25:34PM -0400, Qian Cai wrote:
> 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 <[email protected]>
Looks good,
Reviewed-by: Christoph Hellwig <[email protected]>
On Mon, Aug 31, 2020 at 01:25:34PM -0400, Qian Cai wrote:
> + 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.
> + */
> + path = file_path(dio->iocb->ki_filp, pathname,
> + sizeof(pathname));
> + if (IS_ERR(path))
> + path = "(unknown)";
> +
> + pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %s Comm: %.20s\n",
> + path, current->comm);
"File: %pD4"?
On Mon, Aug 31, 2020 at 06:42:19PM +0100, Matthew Wilcox wrote:
> On Mon, Aug 31, 2020 at 01:25:34PM -0400, Qian Cai wrote:
> > + 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.
> > + */
> > + path = file_path(dio->iocb->ki_filp, pathname,
> > + sizeof(pathname));
> > + if (IS_ERR(path))
> > + path = "(unknown)";
> > +
> > + pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %s Comm: %.20s\n",
> > + path, current->comm);
>
> "File: %pD4"?
Sounds like a good idea. I could use that.