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authorJohn Fastabend <john.fastabend@gmail.com>2020-01-11 06:12:04 +0000
committerDaniel Borkmann <daniel@iogearbox.net>2020-01-15 23:26:13 +0100
commitd468e4775c1c351616947ba0cccc43273963b9b5 (patch)
tree5cd6d430f80dbb320da7033fee90694ed9054bf2 /net
parentcf21e9ba1eb86c9333ca5b05b2f1cc94021bcaef (diff)
bpf: Sockmap/tls, tls_sw can create a plaintext buf > encrypt buf
It is possible to build a plaintext buffer using push helper that is larger than the allocated encrypt buffer. When this record is pushed to crypto layers this can result in a NULL pointer dereference because the crypto API expects the encrypt buffer is large enough to fit the plaintext buffer. Kernel splat below. To resolve catch the cases this can happen and split the buffer into two records to send individually. Unfortunately, there is still one case to handle where the split creates a zero sized buffer. In this case we merge the buffers and unmark the split. This happens when apply is zero and user pushed data beyond encrypt buffer. This fixes the original case as well because the split allocated an encrypt buffer larger than the plaintext buffer and the merge simply moves the pointers around so we now have a reference to the new (larger) encrypt buffer. Perhaps its not ideal but it seems the best solution for a fixes branch and avoids handling these two cases, (a) apply that needs split and (b) non apply case. The are edge cases anyways so optimizing them seems not necessary unless someone wants later in next branches. [ 306.719107] BUG: kernel NULL pointer dereference, address: 0000000000000008 [...] [ 306.747260] RIP: 0010:scatterwalk_copychunks+0x12f/0x1b0 [...] [ 306.770350] Call Trace: [ 306.770956] scatterwalk_map_and_copy+0x6c/0x80 [ 306.772026] gcm_enc_copy_hash+0x4b/0x50 [ 306.772925] gcm_hash_crypt_remain_continue+0xef/0x110 [ 306.774138] gcm_hash_crypt_continue+0xa1/0xb0 [ 306.775103] ? gcm_hash_crypt_continue+0xa1/0xb0 [ 306.776103] gcm_hash_assoc_remain_continue+0x94/0xa0 [ 306.777170] gcm_hash_assoc_continue+0x9d/0xb0 [ 306.778239] gcm_hash_init_continue+0x8f/0xa0 [ 306.779121] gcm_hash+0x73/0x80 [ 306.779762] gcm_encrypt_continue+0x6d/0x80 [ 306.780582] crypto_gcm_encrypt+0xcb/0xe0 [ 306.781474] crypto_aead_encrypt+0x1f/0x30 [ 306.782353] tls_push_record+0x3b9/0xb20 [tls] [ 306.783314] ? sk_psock_msg_verdict+0x199/0x300 [ 306.784287] bpf_exec_tx_verdict+0x3f2/0x680 [tls] [ 306.785357] tls_sw_sendmsg+0x4a3/0x6a0 [tls] test_sockmap test signature to trigger bug, [TEST]: (1, 1, 1, sendmsg, pass,redir,start 1,end 2,pop (1,2),ktls,): Fixes: d3b18ad31f93d ("tls: add bpf support to sk_msg handling") Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/bpf/20200111061206.8028-7-john.fastabend@gmail.com
Diffstat (limited to 'net')
-rw-r--r--net/tls/tls_sw.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index c6803a82b769..31f6bbbc8992 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -682,12 +682,32 @@ static int tls_push_record(struct sock *sk, int flags,
split_point = msg_pl->apply_bytes;
split = split_point && split_point < msg_pl->sg.size;
+ if (unlikely((!split &&
+ msg_pl->sg.size +
+ prot->overhead_size > msg_en->sg.size) ||
+ (split &&
+ split_point +
+ prot->overhead_size > msg_en->sg.size))) {
+ split = true;
+ split_point = msg_en->sg.size;
+ }
if (split) {
rc = tls_split_open_record(sk, rec, &tmp, msg_pl, msg_en,
split_point, prot->overhead_size,
&orig_end);
if (rc < 0)
return rc;
+ /* This can happen if above tls_split_open_record allocates
+ * a single large encryption buffer instead of two smaller
+ * ones. In this case adjust pointers and continue without
+ * split.
+ */
+ if (!msg_pl->sg.size) {
+ tls_merge_open_record(sk, rec, tmp, orig_end);
+ msg_pl = &rec->msg_plaintext;
+ msg_en = &rec->msg_encrypted;
+ split = false;
+ }
sk_msg_trim(sk, msg_en, msg_pl->sg.size +
prot->overhead_size);
}

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