Hi.
Looks like we can memcpy more than we allocated in nft_set_elem_init().
reproducer:
nft -f /etc/nftables/ipv4-filter
nft add map filter ipmap '{ type ipv4_addr : verdict; }'
nft add chain filter foo
nft add element filter ipmap { 1.2.3.4 : jump foo }
-> we scribble over elem private size
You can see this when turning on SLUB debugging and deleting the jump
element again, we get 'Redzone overwritten'.
In nft_add_set_elem() we try to account for the length:
3372
3373 if (nla[NFTA_SET_ELEM_DATA] != NULL) {
3374 err = nft_data_init(ctx, &data, sizeof(data), &d2,
3375 nla[NFTA_SET_ELEM_DATA]);
3376 if (err < 0)
3377 goto err2;
[..]
3380 if (set->dtype != NFT_DATA_VERDICT && d2.len != set->dlen)
3381 goto err3;
3401 nft_set_ext_add_length(&tmpl, NFT_SET_EXT_DATA, d2.len);
3402 }
but in above 'nft add element filter ipmap { 1.2.3.4 : jump foo }'
We have dtype NFT_DATA_VERDICT, d2.len of 8, and set->dlen of 16.
So account for d2.len (8), but then later copy a size of set->dlen (16) in
nft_set_elem_init:
3272 if (nft_set_ext_exists(ext, NFT_SET_EXT_DATA))
3273 memcpy(nft_set_ext_data(ext), data, set->dlen);
Could someone please look at this? I'm not sure what the intent is/was.
My hunch is that the check should be
if (set->dtype != NFT_DATA_VERDICT || d2.len != set->dlen)
and libnftnl should also send a dlen of 16, like it already does for
accept/drop.
Thanks,
Florian
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