linux-kernel - [PATCH 3.16 043/202] fuse: handle zero sized retrieve correctly

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Message-ID: <lsq.1556377989.16179724@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        syzbot+c1e36d30ee3416289cc0@...kaller.appspotmail.com,
        "Miklos Szeredi" <mszeredi@...hat.com>
Subject: [PATCH 3.16 043/202] fuse: handle zero sized retrieve correctly

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@...hat.com>

commit 97e1532ef81acb31c30f9e75bf00306c33a77812 upstream.

Dereferencing req->page_descs[0] will Oops if req->max_pages is zero.

Reported-by: syzbot+c1e36d30ee3416289cc0@...kaller.appspotmail.com
Tested-by: syzbot+c1e36d30ee3416289cc0@...kaller.appspotmail.com
Fixes: b2430d7567a3 ("fuse: add per-page descriptor <offset, length> to fuse_req")
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/fuse/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1652,7 +1652,6 @@ static int fuse_retrieve(struct fuse_con
 	req->in.h.nodeid = outarg->nodeid;
 	req->in.numargs = 2;
 	req->in.argpages = 1;
-	req->page_descs[0].offset = offset;
 	req->end = fuse_retrieve_end;
 
 	index = outarg->offset >> PAGE_CACHE_SHIFT;
@@ -1667,6 +1666,7 @@ static int fuse_retrieve(struct fuse_con
 
 		this_num = min_t(unsigned, num, PAGE_CACHE_SIZE - offset);
 		req->pages[req->num_pages] = page;
+		req->page_descs[req->num_pages].offset = offset;
 		req->page_descs[req->num_pages].length = this_num;
 		req->num_pages++;