Patch "nfsd: don't replace page in rq_pages if it's a continuation of last page" has been added to the 6.2-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nfsd: don't replace page in rq_pages if it's a continuation of last page

to the 6.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-don-t-replace-page-in-rq_pages-if-it-s-a-contin.patch
and it can be found in the queue-6.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d88f1378700e3c11231806d2c48aee7afe54d2fc
Author: Jeff Layton <jlayton@xxxxxxxxxx>
Date:   Fri Mar 17 13:13:08 2023 -0400

    nfsd: don't replace page in rq_pages if it's a continuation of last page
    
    [ Upstream commit 27c934dd8832dd40fd34776f916dc201e18b319b ]
    
    The splice read calls nfsd_splice_actor to put the pages containing file
    data into the svc_rqst->rq_pages array. It's possible however to get a
    splice result that only has a partial page at the end, if (e.g.) the
    filesystem hands back a short read that doesn't cover the whole page.
    
    nfsd_splice_actor will plop the partial page into its rq_pages array and
    return. Then later, when nfsd_splice_actor is called again, the
    remainder of the page may end up being filled out. At this point,
    nfsd_splice_actor will put the page into the array _again_ corrupting
    the reply. If this is done enough times, rq_next_page will overrun the
    array and corrupt the trailing fields -- the rq_respages and
    rq_next_page pointers themselves.
    
    If we've already added the page to the array in the last pass, don't add
    it to the array a second time when dealing with a splice continuation.
    This was originally handled properly in nfsd_splice_actor, but commit
    91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()") removed the check
    for it.
    
    Fixes: 91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()")
    Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
    Reported-by: Dario Lesca <d.lesca@xxxxxxxxxx>
    Tested-by: David Critch <dcritch@xxxxxxxxxx>
    Link: https://bugzilla.redhat.com/show_bug.cgi?id=2150630
    Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index bb1e85586dfdd..5308070a47f38 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -937,8 +937,15 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 	struct page *last_page;
 
 	last_page = page + (offset + sd->len - 1) / PAGE_SIZE;
-	for (page += offset / PAGE_SIZE; page <= last_page; page++)
+	for (page += offset / PAGE_SIZE; page <= last_page; page++) {
+		/*
+		 * Skip page replacement when extending the contents
+		 * of the current page.
+		 */
+		if (page == *(rqstp->rq_next_page - 1))
+			continue;
 		svc_rqst_replace_page(rqstp, page);
+	}
 	if (rqstp->rq_res.page_len == 0)	// first call
 		rqstp->rq_res.page_base = offset % PAGE_SIZE;
 	rqstp->rq_res.page_len += sd->len;