FAILED: patch "[PATCH] SUNRPC: svcauth_gss: avoid NULL deref on zero length" failed to apply to 6.1-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x d4b69a6186b215d2dc1ebcab965ed88e8d41768d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025122940-ember-smilingly-3df0@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d4b69a6186b215d2dc1ebcab965ed88e8d41768d Mon Sep 17 00:00:00 2001
From: Joshua Rogers <linux@joshua.hu>
Date: Fri, 7 Nov 2025 10:05:33 -0500
Subject: [PATCH] SUNRPC: svcauth_gss: avoid NULL deref on zero length
 gss_token in gss_read_proxy_verf

A zero length gss_token results in pages == 0 and in_token->pages[0]
is NULL. The code unconditionally evaluates
page_address(in_token->pages[0]) for the initial memcpy, which can
dereference NULL even when the copy length is 0. Guard the first
memcpy so it only runs when length > 0.

Fixes: 5866efa8cbfb ("SUNRPC: Fix svcauth_gss_proxy_init()")
Cc: stable@vger.kernel.org
Signed-off-by: Joshua Rogers <linux@joshua.hu>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index a8ec30759a18..e2f0df8cdaa6 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -1083,7 +1083,8 @@ static int gss_read_proxy_verf(struct svc_rqst *rqstp,
 	}
 
 	length = min_t(unsigned int, inlen, (char *)xdr->end - (char *)xdr->p);
-	memcpy(page_address(in_token->pages[0]), xdr->p, length);
+	if (length)
+		memcpy(page_address(in_token->pages[0]), xdr->p, length);
 	inlen -= length;
 
 	to_offs = length;