linux-kernel - [PATCH v2 42/53] afs: Fix afs_write

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Date:   Fri, 22 Oct 2021 20:08:33 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     Jeff Layton <jlayton@...nel.org>, Jeff Layton <jlayton@...nel.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        linux-afs@...ts.infradead.org, dhowells@...hat.com,
        Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...nel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 42/53] afs: Fix afs_write_end() to handle len > page size

It is possible for the len argument to afs_write_end() to overrun the end
of the page (len is used to key the size of the page in afs_write_start()
when compound pages become a regular thing).

Fix afs_write_end() to correctly trim the write length so that it doesn't
exceed the end of the page.

Fixes: 3003bbd0697b ("afs: Use the netfs_write_begin() helper")
Reported-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Jeff Layton <jlayton@...nel.org>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: Al Viro <viro@...iv.linux.org.uk>
cc: Matthew Wilcox <willy@...radead.org>
cc: linux-afs@...ts.infradead.org
Link: https://lore.kernel.org/r/162367682522.460125.5652091227576721609.stgit@warthog.procyon.org.uk/ # v1
---

 fs/afs/write.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index ced72c6b9a80..19be3153d610 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -119,6 +119,7 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 	_enter("{%llx:%llu},{%lx}",
 	       vnode->fid.vid, vnode->fid.vnode, page->index);
 
+	len = min_t(size_t, len, thp_size(page) - from);
 	if (!PageUptodate(page)) {
 		if (copied < len) {
 			copied = 0;