A corrupted journal may map multiple logical blocks to physical block of
journal superblock and lead journal superblock to be overwriten.
I've seen the following bug when testing on such a corrupted ext4 image.
The journal was corrupted and the extent was like
Displaying leaf extents for inode 8
0:[0]6:27 6:[0]15:26 21:[0]1003:306
Journal superblock is at offset 27 and 7th block is mapped to 27 too.
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffffa01fb8f6>] jbd2_journal_commit_transaction+0x936/0x1a60 [jbd2]
PGD 0
Oops: 0000 [#1] SMP
...
CPU: 2 PID: 12019 Comm: jbd2/loop0-8 Not tainted 4.0.0-rc3+ #16
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
task: ffff8802145e5f60 ti: ffff8800362f0000 task.ti: ffff8800362f0000
RIP: 0010:[<ffffffffa01fb8f6>] [<ffffffffa01fb8f6>] jbd2_journal_commit_transaction+0x936/0x1a60 [jbd2]
...
Stack:
ffff8800362f3cb8 ffff880212717b98 000010e6644a258e 0000001c145e5fc8
ffff8800da9d719c 000000000000000c 000007d8ffffffff ffff880212710810
ffff880212710800 ffff8800da9d7150 ffff880212717824 ffff8800362f3d68
Call Trace:
[<ffffffff810abeb7>] ? set_next_entity+0x67/0x80
[<ffffffff8101358c>] ? __switch_to+0xdc/0x580
[<ffffffffa020041a>] kjournald2+0xca/0x260 [jbd2]
[<ffffffff810bb4d0>] ? prepare_to_wait_event+0xf0/0xf0
[<ffffffffa0200350>] ? commit_timeout+0x10/0x10 [jbd2]
[<ffffffff81097258>] kthread+0xd8/0xf0
[<ffffffff81097180>] ? kthread_create_on_node+0x1b0/0x1b0
[<ffffffff816c93d8>] ret_from_fork+0x58/0x90
[<ffffffff81097180>] ? kthread_create_on_node+0x1b0/0x1b0
...
RIP [<ffffffffa01fb8f6>] jbd2_journal_commit_transaction+0x936/0x1a60 [jbd2]
RSP <ffff8800362f3c88>
CR2: 0000000000000000
So validate the physical block in jbd2_journal_bmap() first to make sure
it's not the journal superblock if superblock is not requested.
Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
---
fs/jbd2/journal.c | 18 ++++++++++++++----
include/linux/jbd2.h | 2 ++
2 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index b96bd80..46208a8 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -789,15 +789,24 @@ int jbd2_journal_bmap(journal_t *journal, unsigned long blocknr,
if (journal->j_inode) {
ret = bmap(journal->j_inode, blocknr);
- if (ret)
- *retp = ret;
- else {
+ if (ret) {
+ if (blocknr != 0 && ret == journal->j_sb_block) {
+ printk(KERN_ALERT "%s: journal block %lu mapped"
+ " to journal superblock(%llu) on %s\n",
+ __func__, blocknr, journal->j_sb_block,
+ journal->j_devname);
+ err = -EIO;
+ } else {
+ *retp = ret;
+ }
+ } else {
printk(KERN_ALERT "%s: journal block not found "
"at offset %lu on %s\n",
__func__, blocknr, journal->j_devname);
err = -EIO;
- __journal_abort_soft(journal, err);
}
+ if (err)
+ __journal_abort_soft(journal, err);
} else {
*retp = blocknr; /* +journal->j_blk_offset */
}
@@ -1245,6 +1254,7 @@ journal_t * jbd2_journal_init_inode (struct inode *inode)
goto out_err;
}
journal->j_sb_buffer = bh;
+ journal->j_sb_block = (unsigned long long)bh->b_blocknr;
journal->j_superblock = (journal_superblock_t *)bh->b_data;
return journal;
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 20e7f78..9a1aee7 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -691,6 +691,7 @@ jbd2_time_diff(unsigned long start, unsigned long end)
* prior abort)?
* @j_sb_buffer: First part of superblock buffer
* @j_superblock: Second part of superblock buffer
+ * @j_sb_block: Physical block number of superblock
* @j_format_version: Version of the superblock format
* @j_state_lock: Protect the various scalars in the journal
* @j_barrier_count: Number of processes waiting to create a barrier lock
@@ -767,6 +768,7 @@ struct journal_s
/* The superblock buffer */
struct buffer_head *j_sb_buffer;
journal_superblock_t *j_superblock;
+ unsigned long long j_sb_block;
/* Version of the superblock format */
int j_format_version;
--
1.8.3.1
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