On Mon, Oct 21, 2013 at 06:06:23PM +0200, Lukáš Czerner wrote:
> On Sun, 20 Oct 2013, Eryu Guan wrote:
...
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index c9ebcb9..855b11d 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -387,11 +387,21 @@ static int ext4_valid_extent_entries(struct inode *inode,
> > if (depth == 0) {
> > /* leaf entries */
> > struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
> > + ext4_lblk_t block = 0;
> > + ext4_lblk_t prev = 0;
> > + int len = 0;
> > while (entries) {
> > if (!ext4_valid_extent(inode, ext))
> > return 0;
> > +
> > + /* Check for overlapping extents */
> > + block = le32_to_cpu(ext->ee_block);
> > + len = ext4_ext_get_actual_len(ext);
> > + if ((block <= prev) && prev)
>
> Both ext4_valid_extent() and ext4_valid_extent_idx() are setting
> s_last_error_block in the case of error. Maybe we should to the same
> here ? Note that the block saved in that variable is physical, not
> logical.
I think that makes sense, it's better to keep the consistency.
But it seems that the s_last_error_block will eventually be
overwritten by ext4_error_inode() in __ext4_ext_check() ?
>
> Also I am curious what happens when one of the extents is corrupted
> in such a way that it crosses the 16TB boundary ? In this case the
> check would not recognise that since prev will underflow, but maybe
> something else catches that ?
Do you mean that a previous (ee_block + len - 1) could cross the 2**32
boundary? I think we can add another check in ext4_valid_extent() for
this situation.
I update the patch to a v3 version, could you please review again?
Thanks a lot!
Eryu Guan
---
>From 467025c05bce3ee44e607887bc7cb74ff1bfefcb Mon Sep 17 00:00:00 2001
From: Eryu Guan <guaneryu@xxxxxxxxx>
Date: Thu, 17 Oct 2013 23:57:22 +0800
Subject: [PATCH v3] ext4: check for overlapping extents in
ext4_valid_extent_entries()
A corrupted ext4 may have out of order leaf extents, i.e.
extent: lblk 0--1023, len 1024, pblk 9217, flags: LEAF UNINIT
extent: lblk 1000--2047, len 1024, pblk 10241, flags: LEAF UNINIT
^^^^ overlap with previous extent
Reading such extent could hit BUG_ON() in ext4_es_cache_extent().
BUG_ON(end < lblk);
The problem is that __read_extent_tree_block() tries to cache holes as
well but assumes 'lblk' is greater than 'prev' and passes underflowed
length to ext4_es_cache_extent(). Fix it by checking for overlapping
extents in ext4_valid_extent_entries().
I hit this when fuzz testing ext4, and am able to reproduce it by
modifying the on-disk extent by hand.
Also add the check for (ee_block + len - 1) in ext4_valid_extent() to
make sure the value is not overflow.
Ran xfstests on patched ext4 and no regression.
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Lukáš Czerner <lczerner@xxxxxxxxxx>
Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
---
v3: Address comments from Lukas
- set s_last_error_block when there's overlapping extents found
- check for (ee_block + len - 1) in ext4_valid_extent(), value should
not overflow
v2:
- check for overlapping extents explicitly not hide the corruption
fs/ext4/extents.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c9ebcb9..85d977f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -360,8 +360,10 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
{
ext4_fsblk_t block = ext4_ext_pblock(ext);
int len = ext4_ext_get_actual_len(ext);
+ ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
+ ext4_lblk_t last = lblock + len - 1;
- if (len == 0)
+ if (lblock > last)
return 0;
return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
}
@@ -387,11 +389,26 @@ static int ext4_valid_extent_entries(struct inode *inode,
if (depth == 0) {
/* leaf entries */
struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
+ struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
+ ext4_fsblk_t pblock = 0;
+ ext4_lblk_t lblock = 0;
+ ext4_lblk_t prev = 0;
+ int len = 0;
while (entries) {
if (!ext4_valid_extent(inode, ext))
return 0;
+
+ /* Check for overlapping extents */
+ lblock = le32_to_cpu(ext->ee_block);
+ len = ext4_ext_get_actual_len(ext);
+ if ((lblock <= prev) && prev) {
+ pblock = ext4_ext_pblock(ext);
+ es->s_last_error_block = cpu_to_le64(pblock);
+ return 0;
+ }
ext++;
entries--;
+ prev = lblock + len - 1;
}
} else {
struct ext4_extent_idx *ext_idx = EXT_FIRST_INDEX(eh);
--
1.8.3.1
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