From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk 1/3] printk: move printk_info into separate array
Date: Fri, 18 Sep 2020 13:36:06 +0206 [thread overview]
Message-ID: <87k0wrb9vl.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <20200918100602.GB14605@alley>
On 2020-09-18, Petr Mladek <pmladek@suse.com> wrote:
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -1097,6 +1097,7 @@ static char setup_dict_buf[CONSOLE_EXT_LOG_MAX] __initdata;
>>
>> void __init setup_log_buf(int early)
>> {
>> + struct printk_info *new_infos;
>> unsigned int new_descs_count;
>> struct prb_desc *new_descs;
>> struct printk_info info;
>> @@ -1156,6 +1157,17 @@ void __init setup_log_buf(int early)
>> return;
>> }
>>
>> + new_descs_size = new_descs_count * sizeof(struct printk_info);
>
> Must be stored into new variable, e.g. new_infos_size.=
Ack.
>> + new_infos = memblock_alloc(new_descs_size, LOG_ALIGN);
>> + if (unlikely(!new_infos)) {
>> + pr_err("log_buf_len: %zu info bytes not available\n",
>> + new_descs_size);
>> + memblock_free(__pa(new_descs), new_log_buf_len);
>> + memblock_free(__pa(new_dict_buf), new_log_buf_len);
>
> The above two calls have wrong size.
>
> The same problem is there also in the error path when new_descs
> allocation fail. It might be better to handle this using some
> goto err_* tagrets.
>
> Please, fix the old problem in a separate patch.
The "old problem" didn't exist. The problem is introduced with this
series. I will fix it with appropriate goto err_* targets for v2.
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -1726,12 +1762,12 @@ static bool copy_data(struct prb_data_ring *data_ring,
>> /*
>> * Actual cannot be less than expected. It can be more than expected
>> * because of the trailing alignment padding.
>> + *
>> + * Note that invalid @len values can occur because the caller loads
>> + * the value during an allowed data race.
>
> I hope that this will not bite us in the future. The fact is that
> copying the entire struct printk_info in get_desc() is ugly and
> copy_data() has to be careful anyway.
It isn't an issue because the state is verified again at the end of
prb_read(). I added the comment because if all you are looking at is
copy_data(), you may not know that @len was read on a data-race. Whereas
inside of prb_read(), it is obvious that the memcpy() is a data-race.
John Ogness
next prev parent reply other threads:[~2020-09-18 11:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 13:16 [PATCH printk 0/3] printk: move dictionaries to meta data John Ogness
2020-09-17 13:16 ` [PATCH printk 1/3] printk: move printk_info into separate array John Ogness
2020-09-18 10:06 ` Petr Mladek
2020-09-18 11:30 ` John Ogness [this message]
2020-09-17 13:16 ` [PATCH printk 2/3] printk: move dictionary keys to dev_printk_info John Ogness
2020-09-18 6:16 ` Rasmus Villemoes
2020-09-18 12:13 ` Petr Mladek
2020-09-18 12:32 ` Rasmus Villemoes
2020-09-18 14:24 ` Petr Mladek
2020-09-18 11:39 ` Petr Mladek
2020-09-17 13:16 ` [PATCH printk 3/3] printk: remove dict ring John Ogness
2020-09-17 17:59 ` Linus Torvalds
2020-09-18 14:56 ` Petr Mladek
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