diff mbox series

iomap: fix WARN_ON_ONCE() from unprivileged users

Message ID 20200830013057.14664-1-cai@lca.pw
State Superseded
Headers show
Series iomap: fix WARN_ON_ONCE() from unprivileged users | expand

Commit Message

Qian Cai Aug. 30, 2020, 1:30 a.m. UTC
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.
Thanks Dave Chinner for the initial analysis of the racing reproducers.

Signed-off-by: Qian Cai <cai@lca.pw>
---
 fs/iomap/direct-io.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Comments

Darrick J. Wong Aug. 31, 2020, 12:30 a.m. UTC | #1
On Sat, Aug 29, 2020 at 09:30:57PM -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.
> Thanks Dave Chinner for the initial analysis of the racing reproducers.
> 
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  fs/iomap/direct-io.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..6a6b4bc13269 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -389,7 +389,14 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
>  	case IOMAP_INLINE:
>  		return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
>  	default:
> -		WARN_ON_ONCE(1);
> +		/*
> +		 * 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("page_mkwrite() is racing with DIO read (iomap->type = %u).\n",
> +				    iomap->type);

Shouldn't we log the name of triggering process and the file path?  Sort
of like what dio_warn_stale_pagecache does?

--D

>  		return -EIO;
>  	}
>  }
> -- 
> 2.18.4
>
Qian Cai Aug. 31, 2020, 12:46 a.m. UTC | #2
On Sun, Aug 30, 2020 at 05:30:33PM -0700, Darrick J. Wong wrote:
> On Sat, Aug 29, 2020 at 09:30:57PM -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.
> > Thanks Dave Chinner for the initial analysis of the racing reproducers.
> > 
> > Signed-off-by: Qian Cai <cai@lca.pw>
> > ---
> >  fs/iomap/direct-io.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index c1aafb2ab990..6a6b4bc13269 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -389,7 +389,14 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
> >  	case IOMAP_INLINE:
> >  		return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
> >  	default:
> > -		WARN_ON_ONCE(1);
> > +		/*
> > +		 * 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("page_mkwrite() is racing with DIO read (iomap->type = %u).\n",
> > +				    iomap->type);
> 
> Shouldn't we log the name of triggering process and the file path?  Sort
> of like what dio_warn_stale_pagecache does?

Good idea. I'll add them.
diff mbox series

Patch

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index c1aafb2ab990..6a6b4bc13269 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -389,7 +389,14 @@  iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
 	case IOMAP_INLINE:
 		return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
 	default:
-		WARN_ON_ONCE(1);
+		/*
+		 * 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("page_mkwrite() is racing with DIO read (iomap->type = %u).\n",
+				    iomap->type);
 		return -EIO;
 	}
 }