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From: Sascha Hauer <sha@pengutronix.de>
To: Holger Assmann <h.assmann@pengutronix.de>
Cc: barebox@lists.infradead.org, afa@pengutronix.de
Subject: Re: [PATCH] fs: jffs2: fix error when reading blocks with offset
Date: Tue, 7 Dec 2021 09:13:47 +0100
Message-ID: <20211207081347.GC28260@pengutronix.de> (raw)
In-Reply-To: <20211202104837.3912925-1-h.assmann@pengutronix.de>

On Thu, Dec 02, 2021 at 11:48:37AM +0100, Holger Assmann wrote:
> This bug resulted in a panic when trying to read a file partially with
> an offset, e.g. when starting Linux. In such a case a header is loaded
> by a separate call of jffs2_read(), which then copies only the first n
> bytes out of the respective block.
> When the remaining data of the block is then subsequently going to to be
> read the system deviates in its behaviour from that under Linux by not
> calling jffs2_read_inode_range() in a 4k-alignment, but with an offset.
> 
> jffs2_read_inode_range() originates from the Linux jffs2 driver. When
> being called with an offset it still reads 4096 bytes of data and
> eventually returns fragments of two consecutive blocks. jffs2_read()
> then reads this result whilst again applying the offset, therefore
> returning faulty data.
> 
> We fix that problem by calling jffs2_get_block() without an offset and
> therefore reading the whole block. The offset is then applied when we
> actually perform memcpy with the returned buffer. This fix might also
> increase the performance since the respective block is likely to be
> cached from the previous call.
> 
> Signed-off-by: Holger Assmann <h.assmann@pengutronix.de>
> ---
>  fs/jffs2/fs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
> index 1a2b443792..3d4cb98c97 100644
> --- a/fs/jffs2/fs.c
> +++ b/fs/jffs2/fs.c
> @@ -74,6 +74,9 @@ static int jffs2_get_block(struct jffs2_file *jf, unsigned int pos)
>  	struct jffs2_inode_info *f = JFFS2_INODE_INFO(jf->inode);
>  	int ret;
>  
> +	/* pos always has to be 4096 bytes aligned here */
> +	WARN_ON(pos % 4096 != 0);

This should be JFFS2_BLOCK_SIZE, right?

Sascha


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      parent reply	other threads:[~2021-12-07  8:55 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-02 10:48 Holger Assmann
2021-12-03  6:37 ` Ahmad Fatoum
2021-12-07  8:13 ` Sascha Hauer [this message]

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