FAILED: patch "[PATCH] cifs: fix loff_t underflow in cifs_remap_file_range() when" failed to apply to 5.15-stable tree

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 <[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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 6c322f5cf7476ded7a9a20f7be72462065a03c68
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --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 <[email protected]>
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().

index 2073b29ff969..7ecd70efdfea 100644
@@ -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");
 

From: Frank Sorenson <[email protected]>

[ Upstream commit 6c322f5cf7476ded7a9a20f7be72462065a03c68 ]

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().

---
 fs/cifs/cifsfs.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

index 7bdeaecc6c508..e3572c30be4f9 100644
@@ -1171,8 +1171,19 @@ 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, "about to flush pages\n");
 	/* should we flush first and last page first */

@@ -1188,6 +1199,7 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
 	/* force revalidate of size and timestamps of target file now
 	   that target is updated on the server */
 	CIFS_I(target_inode)->time = 0;
+unlock:
 	/* although unlocking in the reverse order from locking is not
 	   strictly necessary here it is a little cleaner to be consistent */
 	unlock_two_nondirectories(src_inode, target_inode);

2.53.0