NFSD: Fix NFSv3 SETATTR/CREATE's handling of large file sizes

[ Upstream commit a648fdeb7c0e17177a2280344d015dba3fbe3314 ]

iattr::ia_size is a loff_t, so these NFSv3 procedures must be
careful to deal with incoming client size values that are larger
than s64_max without corrupting the value.

Silently capping the value results in storing a different value
than the client passed in which is unexpected behavior, so remove
the min_t() check in decode_sattr3().

Note that RFC 1813 permits only the WRITE procedure to return
NFS3ERR_FBIG. We believe that NFSv3 reference implementations
also return NFS3ERR_FBIG when ia_size is too large.

Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
(cherry picked from commit a648fdeb7c0e17177a2280344d015dba3fbe3314)
[Larry: backport to 5.4.y. Minor conflict resolved due to missing commit 9cde9360d18d
NFSD: Update the SETATTR3args decoder to use struct xdr_stream]
Signed-off-by: Larry Bassel <larry.bassel@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>