9pfs: validate count sent by client with T_readdir
A good 9p client sends T_readdir with "count" parameter that's sufficiently smaller than client's initially negotiated msize (maximum message size). We perform a check for that though to avoid the server to be interrupted with a "Failed to encode VirtFS reply type 41" transport error message by bad clients. This count value constraint uses msize - 11, because 11 is the header size of R_readdir. Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Reviewed-by: Greg Kurz <groug@kaod.org> Message-Id: <3990d3891e8ae2074709b56449e96ab4b4b93b7d.1579567020.git.qemu_oss@crudebyte.com> [groug: added comment ] Signed-off-by: Greg Kurz <groug@kaod.org>
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@ -2434,6 +2434,7 @@ static void coroutine_fn v9fs_readdir(void *opaque)
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int32_t count;
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uint32_t max_count;
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V9fsPDU *pdu = opaque;
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V9fsState *s = pdu->s;
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retval = pdu_unmarshal(pdu, offset, "dqd", &fid,
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&initial_offset, &max_count);
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@ -2442,6 +2443,14 @@ static void coroutine_fn v9fs_readdir(void *opaque)
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}
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trace_v9fs_readdir(pdu->tag, pdu->id, fid, initial_offset, max_count);
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/* Enough space for a R_readdir header: size[4] Rreaddir tag[2] count[4] */
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if (max_count > s->msize - 11) {
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max_count = s->msize - 11;
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warn_report_once(
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"9p: bad client: T_readdir with count > msize - 11"
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);
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}
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fidp = get_fid(pdu, fid);
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if (fidp == NULL) {
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retval = -EINVAL;
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