net_sched: fix datalen for ematch

syzbot reported an out-of-bound access in em_nbyte. As initially
analyzed by Eric, this is because em_nbyte sets its own em->datalen
in em_nbyte_change() other than the one specified by user, but this
value gets overwritten later by its caller tcf_em_validate().
We should leave em->datalen untouched to respect their choices.

I audit all the in-tree ematch users, all of those implement
->change() set em->datalen, so we can just avoid setting it twice
in this case.

Reported-and-tested-by: [email protected]
Reported-by: [email protected]
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: Eric Dumazet <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

0 files changed, 0 insertions, 0 deletions