FAILED: patch "[PATCH] NFSD: Fix ia_size underflow" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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]>.

thanks,

greg k-h

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

From e6faac3f58c7c4176b66f63def17a34232a17b0e Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Mon, 31 Jan 2022 13:01:53 -0500
Subject: [PATCH] NFSD: Fix ia_size underflow

iattr::ia_size is a loff_t, which is a signed 64-bit type. NFSv3 and NFSv4 both define file size as an unsigned 64-bit type. Thus there is a range of valid file size values an NFS client can send that is already larger than Linux can handle.

Currently decode_fattr4() dumps a full u64 value into ia_size. If that value happens to be larger than S64_MAX, then ia_size underflows. I'm about to fix up the NFSv3 behavior as well, so let's catch the underflow in the common code path: nfsd_setattr().

index 99c2b9dfbb10..0cccceb105e7 100644
@@ -435,6 +435,10 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
 			.ia_size	= iap->ia_size,
 		};
 
+		host_err = -EFBIG;
+		if (iap->ia_size < 0)
+			goto out_unlock;
+
 		host_err = notify_change(&init_user_ns, dentry, &size_attr, NULL);
 		if (host_err)
 			goto out_unlock;