FAILED: patch "[PATCH] smb: client: harden POSIX SID length parsing" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 7ad2bcf2441430bb2e918fb3ef9a90d775a6e422
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026071425-retiree-hydrant-f109@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 7ad2bcf2441430bb2e918fb3ef9a90d775a6e422 Mon Sep 17 00:00:00 2001
From: Zihan Xi <xizh2024@lzu.edu.cn>
Date: Sun, 28 Jun 2026 17:19:24 +0800
Subject: [PATCH] smb: client: harden POSIX SID length parsing

posix_info_sid_size() reads sid[1] to obtain the subauthority count,
but its existing boundary check still accepts buffers with only one
remaining byte. Require two bytes before reading sid[1] so all client
paths that reuse the helper reject truncated POSIX SIDs safely.

Fixes: 349e13ad30b4 ("cifs: add smb2 POSIX info level")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zihan Xi <xizh2024@lzu.edu.cn>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index d058584b8f05..77738900e75e 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -5405,7 +5405,7 @@ int posix_info_sid_size(const void *beg, const void *end)
 	size_t subauth;
 	int total;
 
-	if (beg + 1 > end)
+	if (beg + 2 > end)
 		return -1;
 
 	subauth = *(u8 *)(beg+1);