linux-kernel - Re: [PATCH] ftrace: Fix null pointer dereference in ftrace_add

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Date:   Thu, 17 Nov 2022 17:17:30 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xiu Jianfeng <xiujianfeng@...wei.com>
Cc:     <mhiramat@...nel.org>, <mark.rutland@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace: Fix null pointer dereference in
 ftrace_add_mod()

On Wed, 16 Nov 2022 09:52:07 +0800
Xiu Jianfeng <xiujianfeng@...wei.com> wrote:

> The @ftrace_mod is allocated by kzalloc(), so both the members {prev,next}
> of @ftrace_mode->list are NULL, it's not a valid state to call list_del().
> If kstrdup() for @ftrace_mod->{func|module} fails, it goes to @out_free
> tag and calls free_ftrace_mod() to destroy @ftrace_mod, then list_del()
> will write prev->next and next->prev, where null pointer dereference
> happens.
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000008
> Oops: 0002 [#1] PREEMPT SMP NOPTI
> Call Trace:
>  <TASK>
>  ftrace_mod_callback+0x20d/0x220
>  ? do_filp_open+0xd9/0x140
>  ftrace_process_regex.isra.51+0xbf/0x130
>  ftrace_regex_write.isra.52.part.53+0x6e/0x90
>  vfs_write+0xee/0x3a0
>  ? __audit_filter_op+0xb1/0x100
>  ? auditd_test_task+0x38/0x50
>  ksys_write+0xa5/0xe0
>  do_syscall_64+0x3a/0x90
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> Kernel panic - not syncing: Fatal exception
> 
> So call INIT_LIST_HEAD() to initialize the list member to fix this issue.
> 
> Fixes: 673feb9d76ab ("ftrace: Add :mod: caching infrastructure to trace_array")
> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
> ---


Queued. Thanks Xiu!

-- Steve