From: Chuck Lever <chuck.lever@oracle.com>
Date: Mon, 31 Jan 2022 13:01:53 -0500
Subject: [PATCH] NFSD: Fix ia_size underflow
Git-commit: e6faac3f58c7c4176b66f63def17a34232a17b0e
Patch-mainline: v5.17
References: git-fixes

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().

Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfsd/vfs.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -448,6 +448,10 @@ nfsd_setattr(struct svc_rqst *rqstp, str
 			.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;