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Message-Id: <20230705215230.9aafc44d8bd764b6416cf655@kernel.org>
Date: Wed, 5 Jul 2023 21:52:30 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: m.stachyra@...sung.com
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-trace-kernel@...r.kernel.org"
<linux-trace-kernel@...r.kernel.org>,
"rostedt@...dmis.org" <rostedt@...dmis.org>,
"mhiramat@...nel.org" <mhiramat@...nel.org>
Subject: Re: [PATCH v2] trace: fix null pointer dereference in
tracing_err_log_open()
On Tue, 04 Jul 2023 12:27:06 +0200
Mateusz Stachyra <m.stachyra@...sung.com> wrote:
> Fix an issue in function 'tracing_err_log_open'.
> The function doesn't call 'seq_open' if file is opened only with
> write permissions, which results in 'file->private_data' being left at null.
> If we then use 'lseek' on that opened file, 'seq_lseek' dereferences
> 'file->private_data' in 'mutex_lock(&m->lock)', resulting in a Kernel panic.
> Writing to this node requires root privilages, therefore this bug
> has very little security impact.
>
> Tracefs node: /sys/kernel/tracing/error_log
>
> Example Kernel panic:
>
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038
> Call trace:
> mutex_lock+0x30/0x110
> seq_lseek+0x34/0xb8
> __arm64_sys_lseek+0x6c/0xb8
> invoke_syscall+0x58/0x13c
> el0_svc_common+0xc4/0x10c
> do_el0_svc+0x24/0x98
> el0_svc+0x24/0x88
> el0t_64_sync_handler+0x84/0xe4
> el0t_64_sync+0x1b4/0x1b8
> Code: d503201f aa0803e0 aa1f03e1 aa0103e9 (c8e97d02)
> ---[ end trace 561d1b49c12cf8a5 ]---
> Kernel panic - not syncing: Oops: Fatal exception
>
Good catch! This looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thanks!
> Signed-off-by: Mateusz Stachyra <m.stachyra@...sung.com>
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> kernel/trace/trace.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index b04f52e7c..4529e264c 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -8146,7 +8146,7 @@ static const struct file_operations tracing_err_log_fops = {
> .open = tracing_err_log_open,
> .write = tracing_err_log_write,
> .read = seq_read,
> - .llseek = seq_lseek,
> + .llseek = tracing_lseek,
> .release = tracing_err_log_release,
> };
>
> --
> 2.25.1
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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