[PATCH v2 2/2] net/9p: fix response size check in p9_check_errors()

[Christian Schoenebeck <linux_oss@crudebyte.com>]

Since commit 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@crudebyte.com>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
---
 net/9p/client.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index c7935e392812..0ff25c2157ab 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -514,10 +514,9 @@ 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 %zu (type=%d)\n",
+		       req->rc.size, req->rc.capacity, req->rc.id);
 		return -EIO;
 	}
 	/* dump the response from server
-- 
2.30.2