[PATCH v3 57/68] afs: Fix afs_write_end() to handle len > page size

[David Howells]

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 at kernel.org>
Signed-off-by: David Howells <dhowells at redhat.com>
Acked-by: Jeff Layton <jlayton at kernel.org>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Al Viro <viro at zeniv.linux.org.uk>
cc: Matthew Wilcox <willy at infradead.org>
cc: linux-afs at lists.infradead.org
Link: https://lore.kernel.org/r/162367682522.460125.5652091227576721609.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163819660464.215744.4576104569408497052.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906968632.143852.17508469800625963114.stgit@warthog.procyon.org.uk/ # v2
---

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

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 8e4e87d66855..9db3ddb1c45b 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -120,6 +120,7 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 	_enter("{%llx:%llu},{%lx}",
 	       vnode->fid.vid, vnode->fid.vnode, folio_index(folio));
 
+	len = min_t(size_t, len, folio_size(folio) - from);
 	if (!folio_test_uptodate(folio)) {
 		if (copied < len) {
 			copied = 0;