FAILED: patch "[PATCH] ksmbd: avoid restoring only in-memory EOF after allocation" 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 9455e920aebe41217cabff3f81e90da4c407fdb6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110313-diagnosis-specimen-de6d@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 9455e920aebe41217cabff3f81e90da4c407fdb6 Mon Sep 17 00:00:00 2001
From: DaeMyung Kang <[email protected]>
Date: Sat, 17 Oct 2026 12:40:50 +0900
Subject: [PATCH] ksmbd: avoid restoring only in-memory EOF after allocation
change

When SetAllocation requests a size below the allocated block count but above EOF, ksmbd truncates the file to that size and restores only the in-memory i_size. The larger EOF remains on disk and reappears after a reboot. A 3-byte file preallocated to 64 KiB can acquire a 4 KiB EOF after reducing its allocation to 4 KiB. Extending EOF this way is not a reliable way to reclaim the preallocation beyond the old EOF either.

Only use this truncate path when the requested allocation is at or below the observed EOF. A truncate to the existing EOF still lets filesystems release preallocated blocks beyond EOF. Remove the in-memory-only i_size restoration. The size check still precedes vfs_truncate() taking the inode lock, so a concurrent shrink can make the truncate extend EOF; that race also existed in the original path.

index 1a0a8cff33bb..9c6345e63434 100644
@@ -8788,24 +8788,17 @@ static int set_file_allocation_info(struct ksmbd_work *work,
 			pr_err("vfs_fallocate is failed : %d\n", rc);
 			return rc;
 		}
-	} else if (alloc_blks < stat.blocks) {
-		loff_t size;
-
+	} else if (alloc_blks < stat.blocks &&
+		   alloc_blks * 512 <= i_size_read(inode)) {
 		/*
-		 * Allocation size could be smaller than original one
-		 * which means allocated blocks in file should be
-		 * deallocated. use truncate to cut out it, but inode
-		 * size is also updated with truncate offset.
-		 * inode size is retained by backup inode size.
+		 * Truncate at or below EOF to discard excess allocation.
+		 * Truncating above EOF would extend the file on disk.
 		 */
-		size = i_size_read(inode);
 		rc = ksmbd_vfs_truncate(work, fp, alloc_blks * 512);
 		if (rc) {
 			pr_err("truncate failed!, err %d\n", rc);
 			return rc;
 		}
-		if (size < alloc_blks * 512)
-			i_size_write(inode, size);
 	}
 
 	fp->allocation_size = le64_to_cpu(file_alloc_info->AllocationSize);

From: DaeMyung Kang <[email protected]>

[ Upstream commit 9455e920aebe41217cabff3f81e90da4c407fdb6 ]

When SetAllocation requests a size below the allocated block count but above EOF, ksmbd truncates the file to that size and restores only the in-memory i_size. The larger EOF remains on disk and reappears after a reboot. A 3-byte file preallocated to 64 KiB can acquire a 4 KiB EOF after reducing its allocation to 4 KiB. Extending EOF this way is not a reliable way to reclaim the preallocation beyond the old EOF either.

Only use this truncate path when the requested allocation is at or below the observed EOF. A truncate to the existing EOF still lets filesystems release preallocated blocks beyond EOF. Remove the in-memory-only i_size restoration. The size check still precedes vfs_truncate() taking the inode lock, so a concurrent shrink can make the truncate extend EOF; that race also existed in the original path.

---
 fs/ksmbd/smb2pdu.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

index 4c42205fe5261..2b43c97a32859 100644
@@ -5887,24 +5887,17 @@ static int set_file_allocation_info(struct ksmbd_work *work,
 			pr_err("vfs_fallocate is failed : %d\n", rc);
 			return rc;
 		}
-	} else if (alloc_blks < stat.blocks) {
-		loff_t size;
-
+	} else if (alloc_blks < stat.blocks &&
+		   alloc_blks * 512 <= i_size_read(inode)) {
 		/*
-		 * Allocation size could be smaller than original one
-		 * which means allocated blocks in file should be
-		 * deallocated. use truncate to cut out it, but inode
-		 * size is also updated with truncate offset.
-		 * inode size is retained by backup inode size.
+		 * Truncate at or below EOF to discard excess allocation.
+		 * Truncating above EOF would extend the file on disk.
 		 */
-		size = i_size_read(inode);
 		rc = ksmbd_vfs_truncate(work, fp, alloc_blks * 512);
 		if (rc) {
 			pr_err("truncate failed!, err %d\n", rc);
 			return rc;
 		}
-		if (size < alloc_blks * 512)
-			i_size_write(inode, size);
 	}
 	return 0;
 }

2.53.0