linux-kernel - [PATCH 2/2] net/9p: fix response size check in p9_check

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Message-Id: <fffb512c532bf1290f0f2b1df6068b2ff6cd14c0.1669072186.git.linux_oss@crudebyte.com>
Date:   Tue, 22 Nov 2022 00:04:08 +0100
From:   Christian Schoenebeck <linux_oss@...debyte.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        GUO Zihua <guozihua@...wei.com>
Subject: [PATCH 2/2] net/9p: fix response size check in p9_check_errors()

Since 60ece0833b6c (net/9p: allocate appropriate reduced message buffers)
it is no longer appropriate to check server's response size against
msize. Check against the previously allocated buffer capacity instead.

 - Omit this size check entirely for zero-copy messages, as those always
   allocate 4k (P9_ZC_HDR_SZ) linear buffers which are not used for actual
   payload and can be much bigger than 4k.

 - Replace p9_debug() by pr_err() to make sure this message is always
   printed in case this error is triggered.

 - Add 9p message type to error message to ease investigation.

Signed-off-by: Christian Schoenebeck <linux_oss@...debyte.com>
---
 net/9p/client.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 30dd82f49b28..63f13dd1ecff 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -514,10 +514,10 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 	int ecode;
 
 	err = p9_parse_header(&req->rc, NULL, &type, NULL, 0);
-	if (req->rc.size >= c->msize) {
-		p9_debug(P9_DEBUG_ERROR,
-			 "requested packet size too big: %d\n",
-			 req->rc.size);
+	if (req->rc.size > req->rc.capacity && !req->rc.zc) {
+		pr_err(
+			 "requested packet size too big: %d does not fit %ld (type=%d)\n",
+			 req->rc.size, req->rc.capacity, req->rc.id);
 		return -EIO;
 	}
 	/* dump the response from server
-- 
2.30.2