Re: [PATCH] migration/migration: fix null pointer dereference in migration block

[Peter Xu <peterx@redhat.com>]

On Thu, Nov 07, 2024 at 02:42:56PM +0300, gerben@altlinux.org wrote:
> From: Denis Rastyogin <gerben@altlinux.org>

Hi, Denis,

Thanks for the patch, there's an identical patch already on the list to fix
it:

https://lore.kernel.org/r/20241105182725.2393425-1-peterx@redhat.com

> 
> In this merge, the migration_is_idle() function was replaced with migrate_is_running().
> However, the null pointer check for `s` was removed, leading to a dereference of `s` 
> when using qemu-system-x86_64 -hda *.vdi.
> A null check for `s` has been added before its use to prevent the dereference.

This is more severe than I thought..  I think I'll send the pull sooner,
and I'll update the commit message a bit too to reflect your report here.

> 
> Fixes: cbad455118 ("Merge tag 'migration-20241030-pull-request' of https://gitlab.com/peterx/qemu into staging")

Definitely not the merge commit to blame..

> Signed-off-by: Denis Rastyogin <gerben@altlinux.org>

Thanks,

> ---
>  migration/migration.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index aedf7f0751..8c5bd0a75c 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1117,6 +1117,10 @@ bool migration_is_running(void)
>  {
>      MigrationState *s = current_migration;
>  
> +    if (!s) {
> +        return false;
> +    }
> +
>      switch (s->state) {
>      case MIGRATION_STATUS_ACTIVE:
>      case MIGRATION_STATUS_POSTCOPY_ACTIVE:
> -- 
> 2.42.2
> 

-- 
Peter Xu