mail archive of the barebox mailing list
 help / color / mirror / Atom feed
From: Holger Assmann <h.assmann@pengutronix.de>
To: barebox@lists.infradead.org
Cc: afa@pengutronix.de, Holger Assmann <h.assmann@pengutronix.de>
Subject: [PATCH] fs: jffs2: fix error when reading blocks with offset
Date: Thu,  2 Dec 2021 11:48:37 +0100	[thread overview]
Message-ID: <20211202104837.3912925-1-h.assmann@pengutronix.de> (raw)

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);
+
 	if (pos != jf->offset) {
 		ret = jffs2_read_inode_range(c, f, jf->buf, pos,
 					     JFFS2_BLOCK_SIZE);
@@ -98,13 +101,14 @@ static int jffs2_read(struct device_d *_dev, FILE *f, void *buf,
 	/* Read till end of current block */
 	ofs = f->pos % JFFS2_BLOCK_SIZE;
 	if (ofs) {
-		ret = jffs2_get_block(jf, pos);
+		ret = jffs2_get_block(jf, f->pos - ofs); /* Align down block */
 		if (ret)
 			return ret;
 
 		now = min(size, JFFS2_BLOCK_SIZE - ofs);
 
-		memcpy(buf, jf->buf + ofs, now);
+		/* Complete block has been read, re-apply ofset now */
+		memcpy(buf, jf->buf + ofs, now); 
 		size -= now;
 		pos += now;
 		buf += now;
-- 
2.30.2


_______________________________________________
barebox mailing list
barebox@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/barebox


             reply	other threads:[~2021-12-02 10:50 UTC|newest]

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

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=20211202104837.3912925-1-h.assmann@pengutronix.de \
    --to=h.assmann@pengutronix.de \
    --cc=afa@pengutronix.de \
    --cc=barebox@lists.infradead.org \
    --subject='Re: [PATCH] fs: jffs2: fix error when reading blocks with offset' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox