[PATCH] commands/videoinfo: Prevent crash when run while video driver already active

[PATCH] commands/videoinfo: Prevent crash when run while video driver already active

[Glenn Washburn]

The videoinfo command will initialize all non-active video adapters. Video
drivers tend to zero out the global framebuffer object on initialization.
This is not a problem when there is no active video adapter. However, when
there is, then outputting to the video adapter will cause a crash because
methods in the framebuffer object are reinitialized. For example, this
comand sequence will cause a crash.

  terminal_output --append gfxterm; videoinfo

When running in a QEMU headless with GRUB built for the x86_64-efi target,
the first command initializes the Bochs video adapter, which, among
other things, sets the set_page() member function. Then when videoinfo is
run, all non-Bochs video adapters will be initialized, each one wiping
the framebuffer and thus setting set_page to NULL. Soon after the videoinfo
command finishes there will be a call to grub_refresh(), which will
ultimately call the framebuffer's set_page which will be NULL and cause
a crash when called.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 grub-core/commands/videoinfo.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/grub-core/commands/videoinfo.c b/grub-core/commands/videoinfo.c
index 5eb969748b0e..205ba78c9f7b 100644
--- a/grub-core/commands/videoinfo.c
+++ b/grub-core/commands/videoinfo.c
@@ -191,6 +191,11 @@ grub_cmd_videoinfo (grub_command_t cmd __attribute__ ((unused)),
 	  /* Don't worry about errors.  */
 	  grub_errno = GRUB_ERR_NONE;
       }
+    else if (id != GRUB_VIDEO_DRIVER_NONE)
+      {
+	grub_puts_ (N_("  A video driver is active, cannot initialize this driver until it is deactivated\n"));
+	continue;
+      }
     else
       {
 	if (adapter->init ())
-- 
2.34.1


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Re: [PATCH] commands/videoinfo: Prevent crash when run while video driver already active

[Daniel Kiper]

On Fri, Aug 11, 2023 at 04:30:04PM -0500, Glenn Washburn wrote:
> The videoinfo command will initialize all non-active video adapters. Video
> drivers tend to zero out the global framebuffer object on initialization.
> This is not a problem when there is no active video adapter. However, when
> there is, then outputting to the video adapter will cause a crash because
> methods in the framebuffer object are reinitialized. For example, this
> comand sequence will cause a crash.
>
>   terminal_output --append gfxterm; videoinfo
>
> When running in a QEMU headless with GRUB built for the x86_64-efi target,
> the first command initializes the Bochs video adapter, which, among
> other things, sets the set_page() member function. Then when videoinfo is
> run, all non-Bochs video adapters will be initialized, each one wiping
> the framebuffer and thus setting set_page to NULL. Soon after the videoinfo
> command finishes there will be a call to grub_refresh(), which will
> ultimately call the framebuffer's set_page which will be NULL and cause
> a crash when called.
>
> Signed-off-by: Glenn Washburn <development@efficientek.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel

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