Commit 4576cd46 authored Aug 06, 2018 by Willem de Bruijn Committed by David S. Miller Aug 06, 2018

packet: refine ring v3 block size test to hold one frame



TPACKET_V3 stores variable length frames in fixed length blocks.
Blocks must be able to store a block header, optional private space
and at least one minimum sized frame.

Frames, even for a zero snaplen packet, store metadata headers and
optional reserved space.

In the block size bounds check, ensure that the frame of the
chosen configuration fits. This includes sockaddr_ll and optional
tp_reserve.

Syzbot was able to construct a ring with insuffient room for the
sockaddr_ll in the header of a zero-length frame, triggering an
out-of-bounds write in dev_parse_header.

Convert the comparison to less than, as zero is a valid snap len.
This matches the test for minimum tp_frame_size immediately below.

Fixes: f6fb8f10 ("af-packet: TPACKET_V3 flexible buffer implementation.")
Fixes: eb73190f ("net/packet: refine check for priv area size")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 82a40777

net/packet/af_packet.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -4226,6 +4226,8 @@ static int packet_set_ring(struct sock sk, union tpacket_req_u req_u,
		}

		if (req->tp_block_nr) {
		unsigned int min_frame_size;

		/* Sanity tests and some calculations */
		err = -EBUSY;
		if (unlikely(rb->pg_vec))
		@@ -4248,12 +4250,12 @@ static int packet_set_ring(struct sock sk, union tpacket_req_u req_u,
		goto out;
		if (unlikely(!PAGE_ALIGNED(req->tp_block_size)))
		goto out;
		min_frame_size = po->tp_hdrlen + po->tp_reserve;
		if (po->tp_version >= TPACKET_V3 &&
		req->tp_block_size <=
		BLK_PLUS_PRIV((u64)req_u->req3.tp_sizeof_priv) + sizeof(struct tpacket3_hdr))
		req->tp_block_size <
		BLK_PLUS_PRIV((u64)req_u->req3.tp_sizeof_priv) + min_frame_size)
		goto out;
		if (unlikely(req->tp_frame_size < po->tp_hdrlen +
		po->tp_reserve))
		if (unlikely(req->tp_frame_size < min_frame_size))
		goto out;
		if (unlikely(req->tp_frame_size & (TPACKET_ALIGNMENT - 1)))
		goto out;

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