[lvc-project] [PATCH] bcachefs: fix potential NULL deref in bch2_sb_members_v2_init

[Kent Overstreet]

On Tue, Dec 02, 2025 at 08:20:46PM +0300, Mikhail Dmitrichenko wrote:
> bch2_sb_members_v2_init calls bch2_sb_field_resize to allocate the
> members_v2 superblock field, but does not check the returned pointer
> before dereferencing it. bch2_sb_field_resize may return NULL if
> superblock reallocation fails. In this case dereferencing mi2=NULL
> will cause crash during superblock upgrade from members_v1 to members_v2.
> 
> Add check for bch2_sb_field_resize call result for NULL.
> sb_members_v2_resize_entries function already has such check and returns
> error in this case. Make bch2_sb_members_v2_init() consistent and return
> the same error.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 3f7b9713dae0 ("bcachefs: New superblock section members_v2")
> Signed-off-by: Mikhail Dmitrichenko <mdmitrichenko at astralinux.ru>

Thanks! Applied.

> ---
>  fs/bcachefs/sb/members.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/bcachefs/sb/members.c b/fs/bcachefs/sb/members.c
> index 8bf8f5ca3470..a610426b6013 100644
> --- a/fs/bcachefs/sb/members.c
> +++ b/fs/bcachefs/sb/members.c
> @@ -116,6 +116,9 @@ int bch2_sb_members_v2_init(struct bch_fs *c)
>  				DIV_ROUND_UP(sizeof(*mi2) +
>  					     sizeof(struct bch_member) * c->sb.nr_devices,
>  					     sizeof(u64)));
> +		if (!mi2)
> +			return bch_err_throw(c, ENOSPC_sb_members_v2);
> +
>  		mi1 = bch2_sb_field_get(c->disk_sb.sb, members_v1);
>  		memcpy(&mi2->_members[0], &mi1->_members[0],
>  		       BCH_MEMBER_V1_BYTES * c->sb.nr_devices);
> -- 
> 2.39.2
>