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ovpn: fix check for skb_to_sgvec_nomark() return value

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Depending on the data offset, skb_to_sgvec_nomark() may use
less scatterlist elements than what was forecasted by the
previous call to skb_cow_data().

It specifically happens when 'skbheadlen(skb) < offset', because
in this case we entirely skip the skb's head, which would have
required its own scatterlist element.

For this reason, it doesn't make sense to check that
skb_to_sgvec_nomark() returns the same value as skb_cow_data(),
but we can rather check for errors only, as it happens in
other parts of the kernel.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
This commit is contained in:
Antonio Quartulli 2025-05-13 01:17:22 +02:00
parent 0ca74dfabd
commit 40d48527a5
1 changed files with 12 additions and 6 deletions
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18
drivers/net/ovpn/crypto_aead.c
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@ -88,12 +88,15 @@ int ovpn_aead_encrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
/* build scatterlist to encrypt packet payload */
ret = skb_to_sgvec_nomark(skb, sg + 1, 0, skb->len);
if (unlikely(nfrags != ret))
return -EINVAL;
if (unlikely(ret < 0)) {
netdev_err(peer->ovpn->dev,
"encrypt: cannot map skb to sg: %d\n", ret);
return ret;
}
/* append auth_tag onto scatterlist */
__skb_push(skb, tag_size);
sg_set_buf(sg + nfrags + 1, skb->data, tag_size);
sg_set_buf(sg + ret + 1, skb->data, tag_size);
/* obtain packet ID, which is used both as a first
* 4 bytes of nonce and last 4 bytes of associated data.
@ -201,11 +204,14 @@ int ovpn_aead_decrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
/* build scatterlist to decrypt packet payload */
ret = skb_to_sgvec_nomark(skb, sg + 1, payload_offset, payload_len);
if (unlikely(nfrags != ret))
return -EINVAL;
if (unlikely(ret < 0)) {
netdev_err(peer->ovpn->dev,
"decrypt: cannot map skb to sg: %d\n", ret);
return ret;
}
/* append auth_tag onto scatterlist */
sg_set_buf(sg + nfrags + 1, skb->data + OVPN_AAD_SIZE, tag_size);
sg_set_buf(sg + ret + 1, skb->data + OVPN_AAD_SIZE, tag_size);
/* iv may be required by async crypto */
ovpn_skb_cb(skb)->iv = kmalloc(OVPN_NONCE_SIZE, GFP_ATOMIC);