virtio-console: avoid DMA from stack

commit c4baad50297d84bde1a7ad45e50c73adae4a2192 upstream.

put_chars() stuffs the buffer it gets into an sg, but that buffer may be
on the stack. This breaks with CONFIG_VMAP_STACK=y (for me, it
manifested as printks getting turned into NUL bytes).

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Brad Spengler <spender@grsecurity.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 15a3ec940723a8f12c9b938a44e1dd6b27511bab..55d8b073cc61127b524c500b2eff3baf1b927fde 100644 (file)
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1130,6 +1130,8 @@ static int put_chars(u32 vtermno, const char *buf, int count)
 {
        struct port *port;
        struct scatterlist sg[1];
+       void *data;
+       int ret;
 
        if (unlikely(early_put_chars))
                return early_put_chars(vtermno, buf, count);
@@ -1138,8 +1140,14 @@ static int put_chars(u32 vtermno, const char *buf, int count)
        if (!port)
                return -EPIPE;
 
-       sg_init_one(sg, buf, count);
-       return __send_to_port(port, sg, 1, count, (void *)buf, false);
+       data = kmemdup(buf, count, GFP_ATOMIC);
+       if (!data)
+               return -ENOMEM;
+
+       sg_init_one(sg, data, count);
+       ret = __send_to_port(port, sg, 1, count, data, false);
+       kfree(data);
+       return ret;
 }
 
 /*