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net: tls: prevent chain-after-chain in plain text SG

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Sashiko points out that if end = 0 (start != 0) the current
code will create a chain link to content type right after
the wrap link:

  This would create a chain where the wrap link points directly
  to another chain link. The scatterlist API sg_next iterator
  does not recursively resolve consecutive chain links.

meaning this is illegal input to crypto.

The wrapping link is unnecessary if end = 0. end is the entry after
the last one used so end = 0 means there's nothing pushed after
the wrap:

   end         start            i
    v            v              v
  [   ]...[   ][ d ][ d ][ d ][ d ][rsv for wrap]

Skip the wrapping in this case.

TLS 1.3 can use the "wrapping slot" for it's chaining if end = 0.
This avoids the chain-after-chain.

Move the wrap chaining before marking END and chaining off content
type, that feels like more logical ordering to me, but should not
matter from functional perspective.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 9aaaa56845 ("bpf: Sockmap/tls, skmsg can have wrapped skmsg that needs extra chaining")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20260511174920.433155-3-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Jakub Kicinski
2026-05-11 10:49:18 -07:00
committed by Paolo Abeni
parent 285943c6e7
commit ff26a0e837
1 changed files with 18 additions and 6 deletions
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24
net/tls/tls_sw.c
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@@ -789,21 +789,33 @@ static int tls_push_record(struct sock *sk, int flags,
i = msg_pl->sg.end;
sk_msg_iter_var_prev(i);
/* msg_pl->sg.data is a ring; data[MAX+1] is reserved for the wrap
* link (frags won't use it). 'i' is now the last filled entry:
*
* i end start
* v v v [ rsv ]
* [ d ][ d ][ ][ ]...[ ][ d ][ d ][ d ][chain]
* ^ END v
* `-----------------------------------------'
*
* Note that SGL does not allow chain-after-chain, so for TLS 1.3,
* we must make sure we don't create the wrap entry and then chain
* link to content_type immediately at index 0.
*/
if (i < msg_pl->sg.start)
sg_chain(msg_pl->sg.data, ARRAY_SIZE(msg_pl->sg.data),
msg_pl->sg.data);
rec->content_type = record_type;
if (prot->version == TLS_1_3_VERSION) {
/* Add content type to end of message. No padding added */
sg_set_buf(&rec->sg_content_type, &rec->content_type, 1);
sg_mark_end(&rec->sg_content_type);
sg_chain(msg_pl->sg.data, msg_pl->sg.end + 1,
&rec->sg_content_type);
sg_chain(msg_pl->sg.data, i + 2, &rec->sg_content_type);
} else {
sg_mark_end(sk_msg_elem(msg_pl, i));
}
if (msg_pl->sg.end < msg_pl->sg.start)
sg_chain(msg_pl->sg.data, ARRAY_SIZE(msg_pl->sg.data),
msg_pl->sg.data);
i = msg_pl->sg.start;
sg_chain(rec->sg_aead_in, 2, &msg_pl->sg.data[i]);