FAILED: patch "[PATCH] smb: client: fix use-before-check of ReparseDataLength in" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 05f78e6cf34ea3a285053bd5999e08e8ac298bd5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090313-underfed-kilogram-a0bd@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 05f78e6cf34ea3a285053bd5999e08e8ac298bd5 Mon Sep 17 00:00:00 2001
From: Frank Sorenson <[email protected]>
Date: Mon, 17 Aug 2026 12:16:57 -0500
Subject: [PATCH] smb: client: fix use-before-check of ReparseDataLength in
reparse_buf_ptr()

reparse_buf_ptr() reads buf->ReparseDataLength before checking that count covers the full fixed header:

    buf = (struct reparse_data_buffer *)((u8 *)io + off);
    len = sizeof(*buf);                          /* 8 bytes */
    rdlen = le16_to_cpu(buf->ReparseDataLength); /* offset 4, 2 bytes */

    if (count < len || count < rdlen + len)      /* check comes after */

struct reparse_data_buffer has ReparseDataLength at offset 4. If a server returns OutputCount < 6, the read at offset 4-5 reaches past the end of the received data. The off+count bounds against iov_len were already validated, but that does not protect against count being smaller than sizeof(*buf).

Split the check: verify count >= sizeof(*buf) before reading ReparseDataLength, then verify count covers the data region.

index bcaa44814b71..98ea5c6c34af 100644
@@ -41,9 +41,11 @@ static struct reparse_data_buffer *reparse_buf_ptr(struct kvec *iov)
 
 	buf = (struct reparse_data_buffer *)((u8 *)io + off);
 	len = sizeof(*buf);
-	rdlen = le16_to_cpu(buf->ReparseDataLength);
+	if (count < len)
+		return ERR_PTR(smb_EIO2(smb_eio_trace_reparse_rdlen, count, 0));
 
-	if (count < len || count < rdlen + len)
+	rdlen = le16_to_cpu(buf->ReparseDataLength);
+	if (count < rdlen + len)
 		return ERR_PTR(smb_EIO2(smb_eio_trace_reparse_rdlen, count, rdlen));
 	return buf;
 }