FAILED: patch "[PATCH] SUNRPC: svcauth_gss: avoid NULL deref on zero length" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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 <[email protected]>.

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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x d4b69a6186b215d2dc1ebcab965ed88e8d41768d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025122941-pupil-strongly-abe3@gregkh' --subject-prefix 'PATCH 5.10.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 <[email protected]>
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.

index a8ec30759a18..e2f0df8cdaa6 100644
@@ -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;

From: Joshua Rogers <[email protected]>

[ Upstream commit d4b69a6186b215d2dc1ebcab965ed88e8d41768d ]

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.

---
 net/sunrpc/auth_gss/svcauth_gss.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 329eac782cc5..fe85762dbd96 100644
@@ -1177,7 +1177,8 @@ static int gss_read_proxy_verf(struct svc_rqst *rqstp,
 	}
 
 	length = min_t(unsigned int, inlen, argv->iov_len);
-	memcpy(page_address(in_token->pages[0]), argv->iov_base, length);
+	if (length)
+		memcpy(page_address(in_token->pages[0]), argv->iov_base, length);
 	inlen -= length;
 
 	to_offs = length;

2.51.0