| Message ID | 20200816071518.6964-1-colyli@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v5,1/3] net: introduce helper sendpage_ok() in include/linux/net.h | expand |
On Sun, Aug 16, 2020 at 1:36 AM Coly Li <colyli@suse.de> wrote: > > The original problem was from nvme-over-tcp code, who mistakenly uses > kernel_sendpage() to send pages allocated by __get_free_pages() without > __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on > tail pages, sending them by kernel_sendpage() may trigger a kernel panic > from a corrupted kernel heap, because these pages are incorrectly freed > in network stack as page_count 0 pages. > > This patch introduces a helper sendpage_ok(), it returns true if the > checking page, > - is not slab page: PageSlab(page) is false. > - has page refcount: page_count(page) is not zero > > All drivers who want to send page to remote end by kernel_sendpage() > may use this helper to check whether the page is OK. If the helper does > not return true, the driver should try other non sendpage method (e.g. > sock_no_sendpage()) to handle the page. Can we leave this helper to mm subsystem? I know it is for sendpage, but its implementation is all about some mm details and its two callers do not belong to net subsystem either. Think this in another way: who would fix it if it is buggy? I bet mm people should. ;) Thanks.
On Sun, Aug 16, 2020 at 10:55:09AM -0700, Cong Wang wrote: > On Sun, Aug 16, 2020 at 1:36 AM Coly Li <colyli@suse.de> wrote: > > > > The original problem was from nvme-over-tcp code, who mistakenly uses > > kernel_sendpage() to send pages allocated by __get_free_pages() without > > __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on > > tail pages, sending them by kernel_sendpage() may trigger a kernel panic > > from a corrupted kernel heap, because these pages are incorrectly freed > > in network stack as page_count 0 pages. > > > > This patch introduces a helper sendpage_ok(), it returns true if the > > checking page, > > - is not slab page: PageSlab(page) is false. > > - has page refcount: page_count(page) is not zero > > > > All drivers who want to send page to remote end by kernel_sendpage() > > may use this helper to check whether the page is OK. If the helper does > > not return true, the driver should try other non sendpage method (e.g. > > sock_no_sendpage()) to handle the page. > > Can we leave this helper to mm subsystem? > > I know it is for sendpage, but its implementation is all about some > mm details and its two callers do not belong to net subsystem either. > > Think this in another way: who would fix it if it is buggy? I bet mm people > should. ;) No. This is all about a really unusual imitation in sendpage, which is pretty much unexpected. In fact the best thing would be to make sock_sendpage do the right thing and call sock_no_sendpage based on this condition, so that driver writers don't have to worry at all.
On Sun, Aug 16, 2020 at 10:45 PM Christoph Hellwig <hch@lst.de> wrote: > > On Sun, Aug 16, 2020 at 10:55:09AM -0700, Cong Wang wrote: > > On Sun, Aug 16, 2020 at 1:36 AM Coly Li <colyli@suse.de> wrote: > > > > > > The original problem was from nvme-over-tcp code, who mistakenly uses > > > kernel_sendpage() to send pages allocated by __get_free_pages() without > > > __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on > > > tail pages, sending them by kernel_sendpage() may trigger a kernel panic > > > from a corrupted kernel heap, because these pages are incorrectly freed > > > in network stack as page_count 0 pages. > > > > > > This patch introduces a helper sendpage_ok(), it returns true if the > > > checking page, > > > - is not slab page: PageSlab(page) is false. > > > - has page refcount: page_count(page) is not zero > > > > > > All drivers who want to send page to remote end by kernel_sendpage() > > > may use this helper to check whether the page is OK. If the helper does > > > not return true, the driver should try other non sendpage method (e.g. > > > sock_no_sendpage()) to handle the page. > > > > Can we leave this helper to mm subsystem? > > > > I know it is for sendpage, but its implementation is all about some > > mm details and its two callers do not belong to net subsystem either. > > > > Think this in another way: who would fix it if it is buggy? I bet mm people > > should. ;) > > No. This is all about a really unusual imitation in sendpage, which So netdev people will have to understand and support PageSlab() or page_count()? If it is unusual even for mm people, how could netdev people suppose to understand this unusual mm bug? At least not any better. > is pretty much unexpected. In fact the best thing would be to make > sock_sendpage do the right thing and call sock_no_sendpage based > on this condition, so that driver writers don't have to worry at all. Agreed, but kernel_sendpage() still relies on mm to provide a helper to make the decision and ensure this helper is always up-to-date. In short, it is all about ownership. Thanks.
On Mon, Aug 17, 2020 at 12:12:12PM -0700, Cong Wang wrote: > > So netdev people will have to understand and support PageSlab() or > page_count()? Yes. As they came up with that contrived rule what is acceptable for sendpage. No one else really knows and other subsystems like the block layer are perfectly fine with it. > > If it is unusual even for mm people, how could netdev people suppose > to understand this unusual mm bug? At least not any better. It is not a mm bug, it is a networking quirk.
diff --git a/include/linux/net.h b/include/linux/net.h index d48ff1180879..a807fad31958 100644 --- a/include/linux/net.h +++ b/include/linux/net.h @@ -21,6 +21,7 @@ #include <linux/rcupdate.h> #include <linux/once.h> #include <linux/fs.h> +#include <linux/mm.h> #include <linux/sockptr.h> #include <uapi/linux/net.h> @@ -286,6 +287,21 @@ do { \ #define net_get_random_once_wait(buf, nbytes) \ get_random_once_wait((buf), (nbytes)) +/* + * E.g. XFS meta- & log-data is in slab pages, or bcache meta + * data pages, or other high order pages allocated by + * __get_free_pages() without __GFP_COMP, which have a page_count + * of 0 and/or have PageSlab() set. We cannot use send_page for + * those, as that does get_page(); put_page(); and would cause + * either a VM_BUG directly, or __page_cache_release a page that + * would actually still be referenced by someone, leading to some + * obscure delayed Oops somewhere else. + */ +static inline bool sendpage_ok(struct page *page) +{ + return (!PageSlab(page) && page_count(page) >= 1); +} + int kernel_sendmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec, size_t num, size_t len); int kernel_sendmsg_locked(struct sock *sk, struct msghdr *msg,
The original problem was from nvme-over-tcp code, who mistakenly uses kernel_sendpage() to send pages allocated by __get_free_pages() without __GFP_COMP flag. Such pages don't have refcount (page_count is 0) on tail pages, sending them by kernel_sendpage() may trigger a kernel panic from a corrupted kernel heap, because these pages are incorrectly freed in network stack as page_count 0 pages. This patch introduces a helper sendpage_ok(), it returns true if the checking page, - is not slab page: PageSlab(page) is false. - has page refcount: page_count(page) is not zero All drivers who want to send page to remote end by kernel_sendpage() may use this helper to check whether the page is OK. If the helper does not return true, the driver should try other non sendpage method (e.g. sock_no_sendpage()) to handle the page. Signed-off-by: Coly Li <colyli@suse.de> Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hannes Reinecke <hare@suse.de> Cc: Jan Kara <jack@suse.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Mikhail Skorzhinskii <mskorzhinskiy@solarflare.com> Cc: Philipp Reisner <philipp.reisner@linbit.com> Cc: Sagi Grimberg <sagi@grimberg.me> Cc: Vlastimil Babka <vbabka@suse.com> Cc: stable@vger.kernel.org --- Changelog: v5, include linux/mm.h in include/linux/net.h v4, change sendpage_ok() as an inline helper, and post it as separate patch. v3, introduce a more common sendpage_ok() v2, fix typo in patch subject v1, the initial version. include/linux/net.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)