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Date:   Fri, 16 Sep 2022 06:31:45 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Dan Carpenter <dan.carpenter@oracle.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Peter Rosin <peda@axentia.se>, Wolfram Sang <wsa@kernel.org>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] i2c: mux: harden i2c_mux_alloc() against integer
 overflows
Message-ID: <202209160630.CF7AE9708D@keescook>
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On Fri, Sep 16, 2022 at 11:23:25AM +0300, Dan Carpenter wrote:
> [...]
> net/ipv6/mcast.c:450 ip6_mc_source() saving 'size_add' to type 'int'

Interesting! Are you able to report the consumer? e.g. I think a bunch
of these would be fixed by:


diff --git a/net/core/sock.c b/net/core/sock.c
index 4cb957d934a2..f004c4d411e3 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2552,10 +2552,11 @@ struct sk_buff *sock_omalloc(struct sock *sk, unsigned long size,
 /*
  * Allocate a memory block from the socket's option memory buffer.
  */
-void *sock_kmalloc(struct sock *sk, int size, gfp_t priority)
+void *sock_kmalloc(struct sock *sk, size_t size, gfp_t priority)
 {
-	if ((unsigned int)size <= sysctl_optmem_max &&
-	    atomic_read(&sk->sk_omem_alloc) + size < sysctl_optmem_max) {
+	if (size > INT_MAX || size > sysctl_optmem_max)
+		return NULL;
+	if (atomic_read(&sk->sk_omem_alloc) < sysctl_optmem_max - size) {
 		void *mem;
 		/* First do the add, to avoid the race if kmalloc
 		 * might sleep.


-- 
Kees Cook