[PATCH] NFS: Avoid memcpy() run-time warning for struct sockaddr overflows

[Kees Cook]

The 'nfs_server' and 'mount_server' structures include a union of
'struct sockaddr' (with the older 16 bytes max address size) and
'struct sockaddr_storage' which is large enough to hold all the supported
sa_family types (128 bytes max size). The runtime memcpy() buffer overflow
checker is seeing attempts to write beyond the 16 bytes as an overflow,
but the actual expected size is that of 'struct sockaddr_storage'. Adjust
the pointers to the correct union member. Avoids this false positive
run-time warning under CONFIG_FORTIFY_SOURCE:

  memcpy: detected field-spanning write (size 28) of single field "&ctx->nfs_server.address" at fs/nfs/namespace.c:178 (size 16)

Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
Link: https://lore.kernel.org/all/202210110948.26b43120-yujie.liu@xxxxxxxxx
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Anna Schumaker <anna@xxxxxxxxxx>
Cc: linux-nfs@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/nfs/fs_context.c | 2 +-
 fs/nfs/namespace.c  | 2 +-
 fs/nfs/super.c      | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 4da701fd1424..bffa31bb35b9 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -1540,7 +1540,7 @@ static int nfs_init_fs_context(struct fs_context *fc)
 		ctx->version		= nfss->nfs_client->rpc_ops->version;
 		ctx->minorversion	= nfss->nfs_client->cl_minorversion;
 
-		memcpy(&ctx->nfs_server.address, &nfss->nfs_client->cl_addr,
+		memcpy(&ctx->nfs_server._address, &nfss->nfs_client->cl_addr,
 			ctx->nfs_server.addrlen);
 
 		if (fc->net_ns != net) {
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 3295af4110f1..2f336ace7555 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -175,7 +175,7 @@ struct vfsmount *nfs_d_automount(struct path *path)
 	}
 
 	/* for submounts we want the same server; referrals will reassign */
-	memcpy(&ctx->nfs_server.address, &client->cl_addr, client->cl_addrlen);
+	memcpy(&ctx->nfs_server._address, &client->cl_addr, client->cl_addrlen);
 	ctx->nfs_server.addrlen	= client->cl_addrlen;
 	ctx->nfs_server.port	= server->port;
 
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 82944e14fcea..8ea7dfdea427 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -823,7 +823,7 @@ static int nfs_request_mount(struct fs_context *fc,
 	struct nfs_fs_context *ctx = nfs_fc2context(fc);
 	struct nfs_mount_request request = {
 		.sap		= (struct sockaddr *)
-						&ctx->mount_server.address,
+						&ctx->mount_server._address,
 		.dirpath	= ctx->nfs_server.export_path,
 		.protocol	= ctx->mount_server.protocol,
 		.fh		= root_fh,
@@ -854,7 +854,7 @@ static int nfs_request_mount(struct fs_context *fc,
 	 * Construct the mount server's address.
 	 */
 	if (ctx->mount_server.address.sa_family == AF_UNSPEC) {
-		memcpy(request.sap, &ctx->nfs_server.address,
+		memcpy(request.sap, &ctx->nfs_server._address,
 		       ctx->nfs_server.addrlen);
 		ctx->mount_server.addrlen = ctx->nfs_server.addrlen;
 	}
-- 
2.34.1