Re: [PATCH v2] ubifs: Fix use-after-free in ubifs_tnc_end_commit

[Zhihao Cheng]

在 2024/10/9 22:46, Waqar Hameed 写道:
3 nits below.

1. Make the title as 'ubifs: authentication: Fix use-after-free in 
ubifs_tnc_end_commit'

2. At the begining of the commit msg, describe the problem:
After TNC tree inserting(which may trigger a znode split and change the 
znode->parent) and deleting(which may trigger znode freeing), the 
znode->cparent(which still points to a freed znode) may not be updated 
at the begining of commit, which could trigger an UAF problem while 
accessing znode->cparent in write_index().

> Running
>
>    rm -f /etc/test-file.bin
>    dd if=/dev/urandom of=/etc/test-file.bin bs=1M count=60 conv=fsync
>
> in a loop, with `CONFIG_UBIFS_FS_AUTHENTICATION`, KASAN reports:
>
>    BUG: KASAN: use-after-free in ubifs_tnc_end_commit+0xa5c/0x1950
>    Write of size 32 at addr ffffff800a3af86c by task ubifs_bgt0_20/153
>
>    Call trace:

[...]
> diff --git a/fs/ubifs/tnc_commit.c b/fs/ubifs/tnc_commit.c
> index a55e04822d16..a464eb557585 100644
> --- a/fs/ubifs/tnc_commit.c
> +++ b/fs/ubifs/tnc_commit.c
> @@ -657,6 +657,7 @@ static int get_znodes_to_commit(struct ubifs_info *c)
>   		znode->alt = 0;
>   		cnext = find_next_dirty(znode);
>   		if (!cnext) {

3. I'd like to add the the assertion 'ubifs_assert(c, !znode->parent);'
> +			znode->cparent = NULL;
>   			znode->cnext = c->cnext;
>   			break;
>   		}