Re: [PATCH v2 1/2] nfsd: don't replace page in rq_pages if it's a continuation of last page
From: Chuck Lever III <hidden>
Date: 2023-03-17 17:34:13
On Mar 17, 2023, at 1:13 PM, Jeff Layton [off-list ref] wrote:
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 removed the check for it.
Fixes: 91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()")
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Dario Lesca <redacted>
Tested-by: David Critch <redacted>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2150630
Signed-off-by: Jeff Layton <jlayton@kernel.org>I've applied this one internally for due-diligence testing. I'll wait a couple of days for review comments, so it's not likely to make v6.3-rc3 on Sunday.
quoted hunk ↗ jump to hunk
--- fs/nfsd/vfs.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 502e1b7742db..97b38b47c563 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c@@ -941,8 +941,14 @@ 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++) - svc_rqst_replace_page(rqstp, 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)) + 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; -- 2.39.2
-- Chuck Lever