On 2020/9/25 23:18, Greg KH wrote:
On Fri, Sep 25, 2020 at 11:01:13PM +0800, Coly Li 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.
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
include/linux/net.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/include/linux/net.h b/include/linux/net.h index d48ff1180879..05db8690f67e 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;
Do you have one extra ' ' after "return" there?
It should be fixed in next version.
And this feels like a mm thing, why put it in net.h and not mm.h?
This check is specific for kernel_sendpage(), so I want to place it closer to where kernel_sendpage() is declared.
And indeed there was similar discussion about why this helper is not in mm code in v5 series. Christoph supported to place sendpage_ok() in net.h, an uncompleted piece of his opinion was "It is not a mm bug, it is a networking quirk."
Thanks.
Coly Li