Commit f9c2ff22 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: tcp: dctcp_update_alpha() fixes. 



dctcp_alpha can be read by from dctcp_get_info() without
synchro, so use WRITE_ONCE() to prevent compiler from using
dctcp_alpha as a temporary variable.

Also, playing with small dctcp_shift_g (like 1), can expose
an overflow with 32bit values shifted 9 times before divide.

Use an u64 field to avoid this problem, and perform the divide
only if acked_bytes_ecn is not zero.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1edaa7e8

net/ipv4/tcp_dctcp.c

+16 −10
Original line number Original line Diff line number Diff line
@@ -204,20 +204,26 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags) 




	/* Expired RTT */

	/* Expired RTT */

	if (!before(tp->snd_una, ca->next_seq)) {

	if (!before(tp->snd_una, ca->next_seq)) {

		/* For avoiding denominator == 1. */

		u64 bytes_ecn = ca->acked_bytes_ecn;

		if (ca->acked_bytes_total == 0)

		u32 alpha = ca->dctcp_alpha;

			ca->acked_bytes_total = 1;





		/* alpha = (1 - g) * alpha + g * F */

		/* alpha = (1 - g) * alpha + g * F */

		ca->dctcp_alpha = ca->dctcp_alpha -

				  (ca->dctcp_alpha >> dctcp_shift_g) +

				  (ca->acked_bytes_ecn << (10U - dctcp_shift_g)) /

				  ca->acked_bytes_total;





		if (ca->dctcp_alpha > DCTCP_MAX_ALPHA)

		alpha -= alpha >> dctcp_shift_g;

			/* Clamp dctcp_alpha to max. */

		if (bytes_ecn) {

			ca->dctcp_alpha = DCTCP_MAX_ALPHA;

			/* If dctcp_shift_g == 1, a 32bit value would overflow

			 * after 8 Mbytes.

			 */

			bytes_ecn <<= (10 - dctcp_shift_g);

			do_div(bytes_ecn, max(1U, ca->acked_bytes_total));





			alpha = min(alpha + (u32)bytes_ecn, DCTCP_MAX_ALPHA);

		}

		/* dctcp_alpha can be read from dctcp_get_info() without

		 * synchro, so we ask compiler to not use dctcp_alpha

		 * as a temporary variable in prior operations.

		 */

		WRITE_ONCE(ca->dctcp_alpha, alpha);

		dctcp_reset(tp, ca);

		dctcp_reset(tp, ca);

	}

	}

}

}

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