| Message ID | 20200831172534.12464-1-cai@lca.pw (mailing list archive) |
|---|---|
| State | Deferred, archived |
| Headers | show |
| Series | [v3] iomap: Fix WARN_ON_ONCE() from unprivileged users | expand |
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 <cai@lca.pw> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
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.
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;
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@lca.pw> --- 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(+)