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SubjectRe: [V9fs-developer] [PATCH] p9_parse_header() validate PDU length
Tomas Bortoli wrote on Thu, Jul 12, 2018:
> This patch adds checks to the p9_parse_header() function to
> verify that the length found within the header coincides with the actual
> length of the PDU. Furthermore, it checks that the length stays within the
> acceptable range. To do this the patch brings the actual length of the PDU
> from the different transport layers (rdma and virtio). For TCP (trans_fd.c)
> the length is not know before, so we get it from the header but we check it
> anyway that it's within the valid range.
>
> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
> ---
> [..]
> @@ -498,6 +489,21 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
> if (size)
> *size = r_size;
>
> + if (pdu->size != r_size) {
> + err = -EINVAL;
> + goto rewind_and_exit;
> + }
> + if (pdu->size >= pdu->capacity || pdu->size < 7) {
> + p9_debug(P9_DEBUG_ERROR,
> + "requested packet size too big or too small: %d\n",
> + pdu->size);
> + return -EIO;
> + }

Actually, I've been bad advice - this breaks on virtio with zc packets -
a read or ls in a big directory fails with this in dmesg
[ 1006.853775] 9pnet: -- p9_parse_header (17123): requested packet size too big or too small: 4306
[ 1006.853780] 9pnet: -- p9_check_zc_errors (17123): couldn't parse header -5

I haven't given this any thought yet, but dropping the patch for now

--
Dominique

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