[PATCH net 0/2] tls: fix plaintext sk_msg ring over-fill in tls_sw_sendmsg_splice()

An unprivileged local user can oops the kernel by splicing into a kTLS
socket whose open record already has a full plaintext scatterlist ring.

sk_msg_page_add() has no fullness check of its own and
tls_sw_sendmsg_splice() only tests sk_msg_full() at the bottom of its
do-while loop, so a page is always added before the ring is checked.  That
first add writes the reserved slot and wraps sg.end onto sg.start;
sk_msg_iter_dist() then returns 0, sk_msg_full() reports the full ring as
empty, and the loop keeps overwriting live entries while sg.size grows.
Pushing the resulting record drives the AEAD with a cryptlen larger than
the walkable scatterlist, so the walk runs past the end-marked entry and
dereferences the NULL returned by sg_next().

The ring is left full and unpushed across a syscall by the copy path,
which does not set full_record when the fragment it adds is the one that
exactly fills the ring.

No capabilities, namespaces, io_uring, nftables or BPF are involved; a
plain loopback TCP socket with the "tls" ULP attached is enough.
Reproduced as an ordinary user (uid 1000) on stock production configs --
CONFIG_TLS=y, no KASAN, no LOCKDEP, no fault injection -- on 7.2.0-rc4 and
on 6.12.96.  Present since v6.5.

Patch 1 evaluates the loop condition before the first sk_msg_page_add()
instead of after it.  Patch 2 adds a regression test: it oopses an
unpatched kernel and passes with patch 1 applied (924/924 for the whole
tls suite, with CONFIG_CRYPTO_CHACHA20POLY1305, CONFIG_CRYPTO_SM4 and
CONFIG_CRYPTO_ARIA enabled so every cipher variant runs).

I found this with AI assistance, so per
Documentation/process/security-bugs.rst I am treating it as public and
posting here rather than sending it to security@kernel.org.  For the same
reason I am not posting the standalone reproducer; I can send it privately
if that would be useful.

chanyoung (2):
  tls: don't over-fill the plaintext sk_msg ring in
    tls_sw_sendmsg_splice()
  selftests: tls: add a test for splicing onto a full plaintext record

 net/tls/tls_sw.c                  |  4 +--
 tools/testing/selftests/net/tls.c | 52 +++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 2 deletions(-)

-- 
2.43.0