[Devel] [PATCH RH9] fuse: pcs: do not use sendpage on pages which cannot be sendpaged

[Kui Liu]

It looks like the new API iov_iter_get_pages is not safe for use
when trying to get a page from a bvec to be sent by kernel_sendpage().
So just revert back our own implentation where we check the page
before making get_page(), if the page can't be sendpage, fall back
to copy mode.

Affects: #PSBM-146821, #PSBM-146846
https://jira.vzint.dev/browse/PSBM-146821
https://jira.vzint.dev/browse/PSBM-146846
Signed-off-by: Liu Kui <Kui.Liu at acronis.com>
---
 fs/fuse/kio/pcs/pcs_sock_io.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_sock_io.c b/fs/fuse/kio/pcs/pcs_sock_io.c
index 552b82ab398b..20f088d36d6d 100644
--- a/fs/fuse/kio/pcs/pcs_sock_io.c
+++ b/fs/fuse/kio/pcs/pcs_sock_io.c
@@ -143,16 +143,32 @@ static int do_send_one_seg(struct socket *sock, struct iov_iter *it, size_t left
 	}

 	if (iov_iter_is_bvec(it)) {
-		/* Zerocopy */
 		size_t offset;
 		ssize_t len;
 		struct page *page;

-		len = iov_iter_get_pages(it, &page, size, 1, &offset);
-		BUG_ON(len <= 0);
-
-		ret = kernel_sendpage(sock, page, offset, len, flags);
-		put_page(page);
+		/* Only support single page bvec here */
+		BUG_ON(it->bvec->bv_len > PAGE_SIZE);
+
+		page = it->bvec->bv_page;
+		offset = it->bvec->bv_offset + it->iov_offset;
+		len = min(size, it->bvec->bv_len - it->iov_offset);
+
+		if (sendpage_ok(page)) {
+			/* Zero copy */
+			get_page(page);
+			ret = kernel_sendpage(sock, page, offset, len, flags);
+			put_page(page);
+		} else {
+			/* Fall back to copy mode */
+			struct msghdr msg = { .msg_flags = flags };
+			struct kvec kv;
+
+			kv.iov_base = kmap(page) + offset;
+			kv.iov_len = len;
+			ret = kernel_sendmsg(sock, &msg, &kv, 1, size);
+			kunmap(page);
+		}
 	}

 out:
--
2.32.0 (Apple Git-132)

-----Original Message-----
From: Alexey Kuznetsov <kuznet at acronis.com <mailto:kuznet at acronis.com>>
Date: Monday, 17 April 2023 at 10:31 PM
To: Devel <devel at openvz.org <mailto:devel at openvz.org>>, Konstantin Khorenko <khorenko at virtuozzo.com <mailto:khorenko at virtuozzo.com>>, Kui Liu <Kui.Liu at acronis.com <mailto:Kui.Liu at acronis.com>>
Subject: [PATCH RH9] fuse: pcs: do not use sendpage on pages which cannot be sendpaged


Use the same approach as in iscsi iscsi_tcp_segment_map() which makes
the same operation
in the same context.


In vz7 we added iov_iter_get_pages() infrastructure ourselves and we
did it in safe way.
We checked page before doing any manipulations on it right in core of
iov_iter_get_pages()
and terminated iov_iter_get_pages() if the page looked dubious. We
cannot make this now because
this function is used in many places over kernel and not all the
places are sensitive
to origin of pages but all of them definitely will crash if
iov_iter_get_pages() returns error.


This patch will work for now. I still believe this place deserves
further investigation.
It smells like mainstream could be wrong. Look at my comment in code
for the reasons of doubts.


Affects: #PSBM-146821, #PSBM-146846
https://jira.vzint.dev/browse/PSBM-146821 <https://jira.vzint.dev/browse/PSBM-146821>
https://jira.vzint.dev/browse/PSBM-146846 <https://jira.vzint.dev/browse/PSBM-146846>


Signed-off-by: Alexey Kuznetsov <kuznet at acronis.com <mailto:kuznet at acronis.com>>



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