From: Wang Sheng-Hui <shhuiw@gmail.com>
To: chris.mason@fusionio.com, jbacik@fusionio.com,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Btrfs: check range early in map_private_extent_buffer
Date: Tue, 25 Sep 2012 08:24:38 +0800 [thread overview]
Message-ID: <5060F9C6.1070100@gmail.com> (raw)
In-Reply-To: <20120924161742.GL14582@twin.jikos.cz>
On 2012年09月25日 00:17, David Sterba wrote:
> On Mon, Sep 24, 2012 at 12:38:07PM +0800, Wang Sheng-Hui wrote:
>> Check range early to avoid further check/compute in case
>> of range error.
>>
>> Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
>> ---
>> fs/btrfs/extent_io.c | 16 ++++++++--------
>> 1 files changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 4c87847..9250cf5 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -4643,6 +4643,14 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long start,
>> unsigned long end_i = (start_offset + start + min_len - 1) >>
>> PAGE_CACHE_SHIFT;
>>
>> + if (start + min_len > eb->len) {
>> + printk(KERN_ERR "btrfs bad mapping eb start %llu len %lu, "
>> + "wanted %lu %lu\n", (unsigned long long)eb->start,
>> + eb->len, start, min_len);
>> + WARN_ON(1);
>> + return -EINVAL;
>> + }
>> +
>> if (i != end_i)
>> return -EINVAL;
>
> 4665 unsigned long i = (start_offset + start) >> PAGE_CACHE_SHIFT;
> 4666 unsigned long end_i = (start_offset + start + min_len - 1) >>
> 4667 PAGE_CACHE_SHIFT;
>
> so the check above effectively verifies that
>
> min_len - 1 < PAGE_CACHE_SIZE
> AND
> is within the same page
>
> The other check
>
> if (start + min_len > eb->len) {
>
> looks if the requested data do not lie out of the bounds of the extent
> buffer, where min_len is filled with sizeof(something).
>
> So, both the checks look for corrupted metadata, I don't see the need to
> swap them.
Reread the code and it really does the check.
Got it. Thanks for your explanation.
>
> david
prev parent reply other threads:[~2012-09-25 0:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-24 4:38 Btrfs: check range early in map_private_extent_buffer Wang Sheng-Hui
2012-09-24 16:17 ` David Sterba
2012-09-25 0:24 ` Wang Sheng-Hui [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5060F9C6.1070100@gmail.com \
--to=shhuiw@gmail.com \
--cc=chris.mason@fusionio.com \
--cc=jbacik@fusionio.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).