crypto: scomp - Fix wild memory accesses in scomp_free_streams

In order to use scomp_free_streams to free the partially allocted
streams in the allocation error path, move the alg->stream assignment
to the beginning.  Also check for error pointers in scomp_free_streams
before freeing the ctx.

Finally set alg->stream to NULL to not break subsequent attempts
to allocate the streams.

Fixes: 3d72ad4 ("crypto: acomp - Move stream management into scomp layer")
Reported-by: syzkaller <syzkaller@googlegroups.com>
Co-developed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Co-developed-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Author: herbertx

crypto/scompress.c

@@ -111,13 +111,14 @@ static void scomp_free_streams(struct scomp_alg *alg)
 	struct crypto_acomp_stream __percpu *stream = alg->stream;
 	int i;
 
+	alg->stream = NULL;
 	if (!stream)
 		return;
 
 	for_each_possible_cpu(i) {
 		struct crypto_acomp_stream *ps = per_cpu_ptr(stream, i);
 
-		if (!ps->ctx)
+		if (IS_ERR_OR_NULL(ps->ctx))
 			break;
 
 		alg->free_ctx(ps->ctx);
@@ -135,6 +136,8 @@ static int scomp_alloc_streams(struct scomp_alg *alg)
 	if (!stream)
 		return -ENOMEM;
 
+	alg->stream = stream;
+
 	for_each_possible_cpu(i) {
 		struct crypto_acomp_stream *ps = per_cpu_ptr(stream, i);
 
@@ -146,8 +149,6 @@ static int scomp_alloc_streams(struct scomp_alg *alg)
 
 		spin_lock_init(&ps->lock);
 	}
-
-	alg->stream = stream;
 	return 0;
 }