crypto: algif_skcipher - Fixed overflow when sndbuf is page aligned

When sk_sndbuf is not a multiple of PAGE_SIZE, the limit tests
in sendmsg fail as the limit variable becomes negative and we're
using an unsigned comparison.

The same thing can happen if sk_sndbuf is lowered after a sendmsg
call.

This patch fixes this by always taking the signed maximum of limit
and 0 before we perform the comparison.

It also rounds the value of sk_sndbuf down to a multiple of PAGE_SIZE
so that we don't end up allocating a page only to use a small number
of bytes in it because we're bound by sk_sndbuf.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 9b2f440..1f33480 100644 (file)
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -52,12 +52,18 @@ struct skcipher_ctx {
 #define MAX_SGL_ENTS ((PAGE_SIZE - sizeof(struct skcipher_sg_list)) / \
                      sizeof(struct scatterlist) - 1)
 
-static inline bool skcipher_writable(struct sock *sk)
+static inline int skcipher_sndbuf(struct sock *sk)
 {
        struct alg_sock *ask = alg_sk(sk);
        struct skcipher_ctx *ctx = ask->private;
 
-       return ctx->used + PAGE_SIZE <= max_t(int, sk->sk_sndbuf, PAGE_SIZE);
+       return max_t(int, max_t(int, sk->sk_sndbuf & PAGE_MASK, PAGE_SIZE) -
+                         ctx->used, 0);
+}
+
+static inline bool skcipher_writable(struct sock *sk)
+{
+       return PAGE_SIZE <= skcipher_sndbuf(sk);
 }
 
 static int skcipher_alloc_sgl(struct sock *sk)
@@ -245,7 +251,6 @@ static int skcipher_sendmsg(struct kiocb *unused, struct socket *sock,
        struct af_alg_control con = {};
        long copied = 0;
        bool enc = 0;
-       int limit;
        int err;
        int i;
 
@@ -281,9 +286,6 @@ static int skcipher_sendmsg(struct kiocb *unused, struct socket *sock,
                        memcpy(ctx->iv, con.iv->iv, ivsize);
        }
 
-       limit = max_t(int, sk->sk_sndbuf, PAGE_SIZE);
-       limit -= ctx->used;
-
        while (size) {
                struct scatterlist *sg;
                unsigned long len = size;
@@ -309,20 +311,16 @@ static int skcipher_sendmsg(struct kiocb *unused, struct socket *sock,
                        ctx->used += len;
                        copied += len;
                        size -= len;
-                       limit -= len;
                        continue;
                }
 
-               if (limit < PAGE_SIZE) {
+               if (!skcipher_writable(sk)) {
                        err = skcipher_wait_for_wmem(sk, msg->msg_flags);
                        if (err)
                                goto unlock;
-
-                       limit = max_t(int, sk->sk_sndbuf, PAGE_SIZE);
-                       limit -= ctx->used;
                }
 
-               len = min_t(unsigned long, len, limit);
+               len = min_t(unsigned long, len, skcipher_sndbuf(sk));
 
                err = skcipher_alloc_sgl(sk);
                if (err)
@@ -352,7 +350,6 @@ static int skcipher_sendmsg(struct kiocb *unused, struct socket *sock,
                        ctx->used += plen;
                        copied += plen;
                        size -= plen;
-                       limit -= plen;
                        sgl->cur++;
                } while (len && sgl->cur < MAX_SGL_ENTS);
 
@@ -380,7 +377,6 @@ static ssize_t skcipher_sendpage(struct socket *sock, struct page *page,
        struct skcipher_ctx *ctx = ask->private;
        struct skcipher_sg_list *sgl;
        int err = -EINVAL;
-       int limit;
 
        lock_sock(sk);
        if (!ctx->more && ctx->used)
@@ -389,16 +385,10 @@ static ssize_t skcipher_sendpage(struct socket *sock, struct page *page,
        if (!size)
                goto done;
 
-       limit = max_t(int, sk->sk_sndbuf, PAGE_SIZE);
-       limit -= ctx->used;
-
-       if (limit < PAGE_SIZE) {
+       if (!skcipher_writable(sk)) {
                err = skcipher_wait_for_wmem(sk, flags);
                if (err)
                        goto unlock;
-
-               limit = max_t(int, sk->sk_sndbuf, PAGE_SIZE);
-               limit -= ctx->used;
        }
 
        err = skcipher_alloc_sgl(sk);