[PATCH net-next] tipc: potential memory corruption in tipc_crypto_key_rcv()

[Dan Carpenter]

This code uses "skey->keylen" as an memcpy() size and then checks that
it is valid on the next line.  The other problem is that the check has
a potential integer overflow, it's better to use struct_size() for this.

Fixes: 23700da29b83 ("tipc: add automatic rekeying for encryption key")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
---
Hey Kees and Julia,

It would be nice to change tipc_aead_key_size() but I'm not sure how the
UAPI stuff works.  My first attempt at to change it to

        return struct_size(key, key, key->keylen);

broke the build.  I think you guys used Coccinelle to automatically
update these calculations.  Probably this wasn't updated because you
didn't want to break the build either?

 net/tipc/crypto.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
index 40c44101fe8e..291ba276b835 100644
--- a/net/tipc/crypto.c
+++ b/net/tipc/crypto.c
@@ -2281,6 +2281,7 @@ static bool tipc_crypto_key_rcv(struct tipc_crypto *rx, 
struct tipc_msg *hdr)
        u16 key_gen = msg_key_gen(hdr);
        u16 size = msg_data_sz(hdr);
        u8 *data = msg_data(hdr);
+       u32 keylen;
 
        spin_lock(&rx->lock);
        if (unlikely(rx->skey || (key_gen == rx->key_gen && rx->key.keys))) {
@@ -2289,6 +2290,10 @@ static bool tipc_crypto_key_rcv(struct tipc_crypto *rx, 
struct tipc_msg *hdr)
                goto exit;
        }
 
+       keylen = ntohl(*((__be32 *)(data + TIPC_AEAD_ALG_NAME)));
+       if (struct_size(skey, key, keylen) != size)
+               goto exit;
+
        /* Allocate memory for the key */
        skey = kmalloc(size, GFP_ATOMIC);
        if (unlikely(!skey)) {
@@ -2297,18 +2302,11 @@ static bool tipc_crypto_key_rcv(struct tipc_crypto *rx, 
struct tipc_msg *hdr)
        }
 
        /* Copy key from msg data */
-       skey->keylen = ntohl(*((__be32 *)(data + TIPC_AEAD_ALG_NAME)));
+       skey->keylen = keylen;
        memcpy(skey->alg_name, data, TIPC_AEAD_ALG_NAME);
        memcpy(skey->key, data + TIPC_AEAD_ALG_NAME + sizeof(__be32),
               skey->keylen);
 
-       /* Sanity check */
-       if (unlikely(size != tipc_aead_key_size(skey))) {
-               kfree(skey);
-               skey = NULL;
-               goto exit;
-       }
-
        rx->key_gen = key_gen;
        rx->skey_mode = msg_key_mode(hdr);
        rx->skey = skey;
-- 
2.28.0