FAILED: patch "[PATCH] fs: relax assertions on failure to encode file handles" 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 974e3fe0ac61de85015bbe5a4990cf4127b304b2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025011113-overbite-backroom-b95c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 974e3fe0ac61de85015bbe5a4990cf4127b304b2 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <[email protected]>
Date: Thu, 19 Dec 2024 12:53:01 +0100
Subject: [PATCH] fs: relax assertions on failure to encode file handles

Encoding file handles is usually performed by a filesystem >encode_fh() method that may fail for various reasons.

The legacy users of exportfs_encode_fh(), namely, nfsd and name_to_handle_at(2) syscall are ready to cope with the possibility of failure to encode a file handle.

There are a few other users of exportfs_encode_{fh,fid}() that currently have a WARN_ON() assertion when ->encode_fh() fails. Relax those assertions because they are wrong.

The second linked bug report states commit 16aac5ad1fa9 ("ovl: support encoding non-decodable file handles") in v6.6 as the regressing commit, but this is not accurate.

The aforementioned commit only increases the chances of the assertion and allows triggering the assertion with the reproducer using overlayfs, inotify and drop_caches.

Triggering this assertion was always possible with other filesystems and other reasons of ->encode_fh() failures and more particularly, it was also possible with the exact same reproducer using overlayfs that is mounted with options index=on,nfs_export=on also on kernels < v6.6. Therefore, I am not listing the aforementioned commit as a Fixes commit.

Backport hint: this patch will have a trivial conflict applying to v6.6.y, and other trivial conflicts applying to stable kernels < v6.6.

index dec553034027..e933f9c65d90 100644
@@ -47,10 +47,8 @@ static void show_mark_fhandle(struct seq_file *m, struct inode *inode)
 	size = f->handle_bytes >> 2;
 
 	ret = exportfs_encode_fid(inode, (struct fid *)f->f_handle, &size);
-	if ((ret == FILEID_INVALID) || (ret < 0)) {
-		WARN_ONCE(1, "Can't encode file handler for inotify: %d\n", ret);
+	if ((ret == FILEID_INVALID) || (ret < 0))
 		return;
-	}
 
 	f->handle_type = ret;
 	f->handle_bytes = size * sizeof(u32);

index 3601ddfeddc2..56eee9f23ea9 100644
@@ -442,9 +442,8 @@ struct ovl_fh *ovl_encode_real_fh(struct ovl_fs *ofs, struct dentry *real,
 	buflen = (dwords << 2);
 
 	err = -EIO;
-	if (WARN_ON(fh_type < 0) ||
-	    WARN_ON(buflen > MAX_HANDLE_SZ) ||
-	    WARN_ON(fh_type == FILEID_INVALID))
+	if (fh_type < 0 || fh_type == FILEID_INVALID ||
+	    WARN_ON(buflen > MAX_HANDLE_SZ))
 		goto out_err;
 
 	fh->fb.version = OVL_FH_VERSION;