Hi Liu,
> Several users reported this crash of NULL pointer or general protection,
> the story is that we add a rbtree for speedup ulist iteration, and we
> use krealloc() to address ulist growth, and krealloc() use memcpy to copy
> old data to new memory area, so it's OK for an array as it doesn't use
> pointers while it's not OK for a rbtree as it uses pointers.
>
> So krealloc() will mess up our rbtree and it ends up with crash.
>
> Signed-off-by: Liu Bo <bo.li....@oracle.com>
> ---
> v2: fix an use-after-free bug and a finger error(Thanks Zach and Josef).
>
> fs/btrfs/ulist.c | 17 +++++++++++++++++
> 1 files changed, 17 insertions(+), 0 deletions(-)
>
> diff --git a/fs/btrfs/ulist.c b/fs/btrfs/ulist.c
> index 7b417e2..adc9aac 100644
> --- a/fs/btrfs/ulist.c
> +++ b/fs/btrfs/ulist.c
> @@ -205,6 +205,10 @@ int ulist_add_merge(struct ulist *ulist, u64 val, u64
> aux,
> u64 new_alloced = ulist->nodes_alloced + 128;
> struct ulist_node *new_nodes;
> void *old = NULL;
> + int i;
> +
> + for (i = 0; i < ulist->nnodes; i++)
> + rb_erase(&ulist->nodes[i].rb_node, &ulist->root);
>
> /*
> * if nodes_alloced == ULIST_SIZE no memory has been allocated
> @@ -224,6 +228,19 @@ int ulist_add_merge(struct ulist *ulist, u64 val, u64
> aux,
>
> ulist->nodes = new_nodes;
> ulist->nodes_alloced = new_alloced;
> +
> + /*
> + * krealloc actually uses memcpy, which does not copy rb_node
> + * pointers, so we have to do it ourselves. Otherwise we may
> + * be bitten by crashes.
> + */
> + for (i = 0; i < ulist->nnodes; i++) {
> + ret = ulist_rbtree_insert(ulist, &ulist->nodes[i]);
ulist_rbtree_insert() don't allocate memory. if ret!=0 here means a logic error
happens.
In this case, BUG_ON() should be triggered.
> + if (ret) {
Another thing is if you want to free ulist memory, you can call ulist_free().
Calling kfree()
directly here is wrong.
By the way, i notice in ulist_add_merge() we have a possible memory leak:
if krealloc() fails, we return -ENOMEM directly, this is wrong.
ulist_free(ulist) should be called.
You can fold this into your this patch.
Otherwise, thanks very much for fixing this issue!
Reviewed-by: Wang Shilong <wangsl-f...@cn.fujitsu.com>
Thanks,
Wang
> + kfree(new_nodes);
> + return -ENOMEM;
> + }
> + }
> }
> ulist->nodes[ulist->nnodes].val = val;
> ulist->nodes[ulist->nnodes].aux = aux;
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