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| State | Superseded |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