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sb_mac() verifies that the superblock + MAC don't exceed 512 bytes.
Because the superblock is currently 64 bytes, this really verifies
mac_size <= 448.  This confuses smatch into thinking that mac_size may
be as large as 448, which is inconsistent with the later code that
assumes the MAC fits in a buffer of size HASH_MAX_DIGESTSIZE (64).

In fact mac_size <= HASH_MAX_DIGESTSIZE is guaranteed by the crypto API,
as that is the whole point of HASH_MAX_DIGESTSIZE.  But, let's be
defensive and explicitly check for this.  This suppresses the false
positive smatch warning.  It does not fix an actual bug.
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202409061401.44rtN1bh-lkp@intel.com/

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>