FAILED: patch "[PATCH] cifs: fix loff_t underflow in cifs_remap_file_range() when" 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 6c322f5cf7476ded7a9a20f7be72462065a03c68
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090322-serotonin-marsupial-e485@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 6c322f5cf7476ded7a9a20f7be72462065a03c68 Mon Sep 17 00:00:00 2001
From: Frank Sorenson <sorenson@redhat.com>
Date: Sat, 22 Aug 2026 16:55:17 -0500
Subject: [PATCH] cifs: fix loff_t underflow in cifs_remap_file_range() when
 len == 0

With len == 0 (clone to EOF), the effective length is computed as:

    len = src_inode->i_size - off;

If off > i_size, this is a negative loff_t, corrupting the ByteCount
in the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range
in filemap_write_and_wait_range().  The existing off >= i_size check
fires only after the ioctl has already been sent.

Snapshot i_size_read() once for both the bounds check and the length
calculation, eliminating the TOCTOU and 32-bit torn-read risk.  Reject
off > src_size with -EINVAL.  Treat off == src_size as a no-op,
consistent with __generic_remap_file_range_prep().

Fixes: 04b38d601239 ("vfs: pull btrfs clone API to vfs layer")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 2073b29ff969..7ecd70efdfea 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -1413,8 +1413,19 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	 */
 	lock_two_nondirectories(target_inode, src_inode);
 
-	if (len == 0)
-		len = src_inode->i_size - off;
+	if (len == 0) {
+		loff_t src_size = i_size_read(src_inode);
+
+		if (off > src_size) {
+			rc = -EINVAL;
+			goto unlock;
+		}
+		len = src_size - off;
+		if (!len) {
+			rc = 0;
+			goto unlock;
+		}
+	}
 
 	cifs_dbg(FYI, "clone range\n");