strp_data_ready resets strp->need_bytes to 0 if strp_peek_len indicates
that the remainder of the message has been received. However,
do_strp_work does not reset strp->need_bytes to 0. If do_strp_work
completes a partial message, the value of strp->need_bytes will continue
to reflect the needed bytes of the previous message, causing
future invocations of strp_data_ready to return early if
strp->need_bytes is less than strp_peek_len. Resetting strp->need_bytes
to 0 in __strp_recv on handing a full message to the upper layer solves
this problem.

__strp_recv also calculates strp->need_bytes using stm->accum_len before
stm->accum_len has been incremented by cand_len. This can cause
strp->need_bytes to be equal to the full length of the message instead
of the full length minus the accumulated length. This, in turn, causes
strp_data_ready to return early, even when there is sufficient data to
complete the partial message. Incrementing stm->accum_len before using
it to calculate strp->need_bytes solves this problem.

Found while testing net/tls_sw recv path.

Fixes: 43a0c675 ("strparser: Stream parser for messages")
Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>