NFSD: Fix ia_size underflow

stable inclusion
from stable-v5.10.221
commit 38d02ba22e43b6fc7d291cf724bc6e3b7be6626b
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IADGCI
CVE: CVE-2022-48828

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=38d02ba22e43b6fc7d291cf724bc6e3b7be6626b



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[ Upstream commit e6faac3f ]

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
[ cel: context adjusted, 2f221d6f has not been applied ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Xia Fukun <xiafukun@huawei.com>