When reading the console, xen overwrites the contents of the buffer,
so there is no need to zero the buffer before passing it to xen.
Instead, add a NULL at the end of the buffer.

While we are at it, change the zalloc() of the buffer back to
malloc() as it was before bdf4131 (libxl: don't leak buf in
libxl_xen_console_read_start error handling, 2013-12-03).  The comment
in that commit message says that the intent of the commit was to
change malloc+memset to zalloc(), but only for the
libxl_xen_console_reader struct, not for the buffer.

Signed-off-by: Javi Merino <javi.merino@cloud.com>
---
 tools/libs/light/libxl_console.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_console.c b/tools/libs/light/libxl_console.c
index 9f736b891335..6c4414fcc1a2 100644
--- a/tools/libs/light/libxl_console.c
+++ b/tools/libs/light/libxl_console.c
@@ -783,7 +783,7 @@ libxl_xen_console_reader *
     unsigned int size = 16384 + 1;
 
     cr = libxl__zalloc(NOGC, sizeof(libxl_xen_console_reader));
-    cr->buffer = libxl__zalloc(NOGC, size);
+    cr->buffer = libxl__malloc(NOGC, size);
     cr->size = size;
     cr->clear = clear;
     cr->incremental = 1;
@@ -813,7 +813,6 @@ int libxl_xen_console_read_line(libxl_ctx *ctx,
     unsigned int nr_chars = cr->size - 1;
     GC_INIT(ctx);
 
-    memset(cr->buffer, 0, cr->size);
     ret = xc_readconsolering(ctx->xch, cr->buffer, &nr_chars,
                              cr->clear, cr->incremental, &cr->index);
     if (ret < 0) {
@@ -823,6 +822,7 @@ int libxl_xen_console_read_line(libxl_ctx *ctx,
     }
     if (!ret) {
         if (nr_chars) {
+            cr->buffer[nr_chars] = '\0';
             *line_r = cr->buffer;
             ret = 1;
         } else {
-- 
2.45.2

On Mon, Sep 02, 2024 at 05:38:38PM +0100, Javi Merino wrote:
> When reading the console, xen overwrites the contents of the buffer,
> so there is no need to zero the buffer before passing it to xen.
> Instead, add a NULL at the end of the buffer.
> 
> While we are at it, change the zalloc() of the buffer back to
> malloc() as it was before bdf4131 (libxl: don't leak buf in
> libxl_xen_console_read_start error handling, 2013-12-03).  The comment
> in that commit message says that the intent of the commit was to
> change malloc+memset to zalloc(), but only for the
> libxl_xen_console_reader struct, not for the buffer.
> 
> Signed-off-by: Javi Merino <javi.merino@cloud.com>

Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

Thanks,

-- 

Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech