[PATCH 3/4] 9p: p9dirent_read: check network-provided name length

[Dominique Martinet <asmadeus@codewreck.org>]

From: Dominique Martinet <dominique.martinet@cea.fr>

strcpy to dirent->d_name could overflow the buffer, use strscpy to check
the provided string length and error out if the size was too big.

While we are here, make the function return an error when the pdu
parsing failed, instead of returning the pdu offset as if it had been a
success...

Addresses-Coverity-ID: 139133 ("Copy into fixed size buffer")
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---
 net/9p/protocol.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index b4d80c533f89..462ba144cb39 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -623,13 +623,19 @@ int p9dirent_read(struct p9_client *clnt, char *buf, int len,
 	if (ret) {
 		p9_debug(P9_DEBUG_9P, "<<< p9dirent_read failed: %d\n", ret);
 		trace_9p_protocol_dump(clnt, &fake_pdu);
-		goto out;
+		return ret;
 	}
 
-	strcpy(dirent->d_name, nameptr);
+	ret = strscpy(dirent->d_name, nameptr, sizeof(dirent->d_name));
+	if (ret < 0) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "On the wire dirent name too long: %s\n",
+			 nameptr);
+		kfree(nameptr);
+		return ret;
+	}
 	kfree(nameptr);
 
-out:
 	return fake_pdu.offset;
 }
 EXPORT_SYMBOL(p9dirent_read);
-- 
2.17.1