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From 8762202dd0d6e46854f786bdb6fb3780a1625efe Mon Sep 17 00:00:00 2001
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From: Eryu Guan <guaneryu@gmail.com>
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Date: Tue, 1 Nov 2011 19:04:59 -0400
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Subject: [PATCH] jbd/jbd2: validate sb->s_first in journal_get_superblock()
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I hit a J_ASSERT(blocknr != 0) failure in cleanup_journal_tail() when
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mounting a fsfuzzed ext3 image. It turns out that the corrupted ext3
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image has s_first = 0 in journal superblock, and the 0 is passed to
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journal->j_head in journal_reset(), then to blocknr in
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cleanup_journal_tail(), in the end the J_ASSERT failed.
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So validate s_first after reading journal superblock from disk in
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journal_get_superblock() to ensure s_first is valid.
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The following script could reproduce it:
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fstype=ext3
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blocksize=1024
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img=$fstype.img
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offset=0
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found=0
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magic="c0 3b 39 98"
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dd if=/dev/zero of=$img bs=1M count=8
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mkfs -t $fstype -b $blocksize -F $img
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filesize=`stat -c %s $img`
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while [ $offset -lt $filesize ]
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do
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if od -j $offset -N 4 -t x1 $img | grep -i "$magic";then
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echo "Found journal: $offset"
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found=1
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break
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fi
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offset=`echo "$offset+$blocksize" | bc`
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done
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if [ $found -ne 1 ];then
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echo "Magic \"$magic\" not found"
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exit 1
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fi
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dd if=/dev/zero of=$img seek=$(($offset+23)) conv=notrunc bs=1 count=1
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mkdir -p ./mnt
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mount -o loop $img ./mnt
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Cc: Jan Kara <jack@suse.cz>
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Signed-off-by: Eryu Guan <guaneryu@gmail.com>
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Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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---
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fs/jbd/journal.c | 8 ++++++++
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fs/jbd2/journal.c | 8 ++++++++
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2 files changed, 16 insertions(+), 0 deletions(-)
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diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
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index 9fe061f..fea8dd6 100644
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--- a/fs/jbd/journal.c
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+++ b/fs/jbd/journal.c
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@@ -1135,6 +1135,14 @@ static int journal_get_superblock(journal_t *journal)
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goto out;
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}
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+ if (be32_to_cpu(sb->s_first) == 0 ||
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+ be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
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+ printk(KERN_WARNING
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+ "JBD: Invalid start block of journal: %u\n",
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+ be32_to_cpu(sb->s_first));
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+ goto out;
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+ }
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+
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return 0;
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out:
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diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
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index f24df13..d6e93d0 100644
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--- a/fs/jbd2/journal.c
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+++ b/fs/jbd2/journal.c
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@@ -1251,6 +1251,14 @@ static int journal_get_superblock(journal_t *journal)
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goto out;
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}
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+ if (be32_to_cpu(sb->s_first) == 0 ||
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+ be32_to_cpu(sb->s_first) >= journal->j_maxlen) {
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+ printk(KERN_WARNING
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+ "JBD2: Invalid start block of journal: %u\n",
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+ be32_to_cpu(sb->s_first));
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+ goto out;
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+ }
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+
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return 0;
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out:
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--
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1.7.7.1
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