[PATCH net] strparser: Fix incorrect strp->need_bytes value.

[PATCH net] strparser: Fix incorrect strp->need_bytes value.

[Doron Roberts-Kedes]

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: 43a0c6751a322847 ("strparser: Stream parser for messages")
Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>
---
 net/strparser/strparser.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c
index b9283ce..805b139 100644
--- a/net/strparser/strparser.c
+++ b/net/strparser/strparser.c
@@ -296,9 +296,9 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
 					strp_start_timer(strp, timeo);
 				}
 
+				stm->accum_len += cand_len;
 				strp->need_bytes = stm->strp.full_len -
 						       stm->accum_len;
-				stm->accum_len += cand_len;
 				stm->early_eaten = cand_len;
 				STRP_STATS_ADD(strp->stats.bytes, cand_len);
 				desc->count = 0; /* Stop reading socket */
@@ -321,6 +321,7 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
 		/* Hurray, we have a new message! */
 		cancel_delayed_work(&strp->msg_timer_work);
 		strp->skb_head = NULL;
+		strp->need_bytes = 0;
 		STRP_STATS_INCR(strp->stats.msgs);
 
 		/* Give skb to upper layer */
@@ -410,9 +411,7 @@ void strp_data_ready(struct strparser *strp)
 		return;
 
 	if (strp->need_bytes) {
-		if (strp_peek_len(strp) >= strp->need_bytes)
-			strp->need_bytes = 0;
-		else
+		if (strp_peek_len(strp) < strp->need_bytes)
 			return;
 	}
 
-- 
2.9.5

Re: [PATCH net] strparser: Fix incorrect strp->need_bytes value.

[David Miller]

From: Doron Roberts-Kedes <doronrk@fb.com>
Date: Wed, 11 Apr 2018 15:05:16 -0700

> 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: 43a0c6751a322847 ("strparser: Stream parser for messages")
> Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>

Applied and queued up for -stable.