2019-07-29 03:26:38

by Jia-Ju Bai

Subject: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()

In xchk_da_btree_block_check_sibling(), there is an if statement on
line 274 to check whether ds->state->altpath.blk[level].bp is NULL:
if (ds->state->altpath.blk[level].bp)

When ds->state->altpath.blk[level].bp is NULL, it is used on line 281:
xfs_trans_brelse(..., ds->state->altpath.blk[level].bp);
struct xfs_buf_log_item *bip = bp->b_log_item;
ASSERT(bp->b_transp == tp);

Thus, possible null-pointer dereferences may occur.

To fix these bugs, ds->state->altpath.blk[level].bp is checked before
being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
fs/xfs/scrub/dabtree.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
index 94c4f1de1922..33ff90c0dd70 100644
--- a/fs/xfs/scrub/dabtree.c
+++ b/fs/xfs/scrub/dabtree.c
@@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling(
/* Compare upper level pointer to sibling pointer. */
if (ds->state->altpath.blk[level].blkno != sibling)
xchk_da_set_corrupt(ds, level);
- xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp);
+ if (ds->state->altpath.blk[level].bp)
+ xfs_trans_brelse(ds->dargs.trans,
+ ds->state->altpath.blk[level].bp);
out:
return error;
}
--
2.17.0

2019-07-29 04:42:32

by Darrick J. Wong

Subject: Re: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()

On Mon, Jul 29, 2019 at 11:24:01AM +0800, Jia-Ju Bai wrote:
> In xchk_da_btree_block_check_sibling(), there is an if statement on
> line 274 to check whether ds->state->altpath.blk[level].bp is NULL:
> if (ds->state->altpath.blk[level].bp)
>
> When ds->state->altpath.blk[level].bp is NULL, it is used on line 281:
> xfs_trans_brelse(..., ds->state->altpath.blk[level].bp);
> struct xfs_buf_log_item *bip = bp->b_log_item;
> ASSERT(bp->b_transp == tp);
>
> Thus, possible null-pointer dereferences may occur.
>
> To fix these bugs, ds->state->altpath.blk[level].bp is checked before
> being used.
>
> These bugs are found by a static analysis tool STCheck written by us.
>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> fs/xfs/scrub/dabtree.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
> index 94c4f1de1922..33ff90c0dd70 100644
> --- a/fs/xfs/scrub/dabtree.c
> +++ b/fs/xfs/scrub/dabtree.c
> @@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling(
> /* Compare upper level pointer to sibling pointer. */
> if (ds->state->altpath.blk[level].blkno != sibling)
> xchk_da_set_corrupt(ds, level);
> - xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp);
> + if (ds->state->altpath.blk[level].bp)
> + xfs_trans_brelse(ds->dargs.trans,
> + ds->state->altpath.blk[level].bp);

Indentation here (in xfs we use two spaces)

Also, uh, shouldn't we set ds->state->altpath.blk[level].bp to NULL
since we've released the buffer?

--D

> out:
> return error;
> }
> --
> 2.17.0
>

2019-07-29 07:27:36

by Jia-Ju Bai

Subject: Re: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()

On 2019/7/29 12:20, Darrick J. Wong wrote:
> On Mon, Jul 29, 2019 at 11:24:01AM +0800, Jia-Ju Bai wrote:
>> In xchk_da_btree_block_check_sibling(), there is an if statement on
>> line 274 to check whether ds->state->altpath.blk[level].bp is NULL:
>> if (ds->state->altpath.blk[level].bp)
>>
>> When ds->state->altpath.blk[level].bp is NULL, it is used on line 281:
>> xfs_trans_brelse(..., ds->state->altpath.blk[level].bp);
>> struct xfs_buf_log_item *bip = bp->b_log_item;
>> ASSERT(bp->b_transp == tp);
>>
>> Thus, possible null-pointer dereferences may occur.
>>
>> To fix these bugs, ds->state->altpath.blk[level].bp is checked before
>> being used.
>>
>> These bugs are found by a static analysis tool STCheck written by us.
>>
>> Signed-off-by: Jia-Ju Bai <[email protected]>
>> ---
>> fs/xfs/scrub/dabtree.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
>> index 94c4f1de1922..33ff90c0dd70 100644
>> --- a/fs/xfs/scrub/dabtree.c
>> +++ b/fs/xfs/scrub/dabtree.c
>> @@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling(
>> /* Compare upper level pointer to sibling pointer. */
>> if (ds->state->altpath.blk[level].blkno != sibling)
>> xchk_da_set_corrupt(ds, level);
>> - xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp);
>> + if (ds->state->altpath.blk[level].bp)
>> + xfs_trans_brelse(ds->dargs.trans,
>> + ds->state->altpath.blk[level].bp);
> Indentation here (in xfs we use two spaces)

Okay, I will fix this.

>
> Also, uh, shouldn't we set ds->state->altpath.blk[level].bp to NULL
> since we've released the buffer?

So I should set ds->state->altpath.blk[level].bp to NULL at the end of
the function xchk_da_btree_block_check_sibling()?
Like:
    if (ds->state->altpath.blk[level].bp)
        xfs_trans_brelse(ds->dargs.trans,
                ds->state->altpath.blk[level].bp);
    ds->state->altpath.blk[level].bp = NULL;


Best wishes,
Jia-Ju Bai

2019-07-29 15:00:00

by Darrick J. Wong

Subject: Re: [PATCH] fs: xfs: Fix possible null-pointer dereferences in xchk_da_btree_block_check_sibling()

On Mon, Jul 29, 2019 at 03:25:04PM +0800, Jia-Ju Bai wrote:
>
>
> On 2019/7/29 12:20, Darrick J. Wong wrote:
> > On Mon, Jul 29, 2019 at 11:24:01AM +0800, Jia-Ju Bai wrote:
> > > In xchk_da_btree_block_check_sibling(), there is an if statement on
> > > line 274 to check whether ds->state->altpath.blk[level].bp is NULL:
> > > if (ds->state->altpath.blk[level].bp)
> > >
> > > When ds->state->altpath.blk[level].bp is NULL, it is used on line 281:
> > > xfs_trans_brelse(..., ds->state->altpath.blk[level].bp);
> > > struct xfs_buf_log_item *bip = bp->b_log_item;
> > > ASSERT(bp->b_transp == tp);
> > >
> > > Thus, possible null-pointer dereferences may occur.
> > >
> > > To fix these bugs, ds->state->altpath.blk[level].bp is checked before
> > > being used.
> > >
> > > These bugs are found by a static analysis tool STCheck written by us.
> > >
> > > Signed-off-by: Jia-Ju Bai <[email protected]>
> > > ---
> > > fs/xfs/scrub/dabtree.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
> > > index 94c4f1de1922..33ff90c0dd70 100644
> > > --- a/fs/xfs/scrub/dabtree.c
> > > +++ b/fs/xfs/scrub/dabtree.c
> > > @@ -278,7 +278,9 @@ xchk_da_btree_block_check_sibling(
> > > /* Compare upper level pointer to sibling pointer. */
> > > if (ds->state->altpath.blk[level].blkno != sibling)
> > > xchk_da_set_corrupt(ds, level);
> > > - xfs_trans_brelse(ds->dargs.trans, ds->state->altpath.blk[level].bp);
> > > + if (ds->state->altpath.blk[level].bp)
> > > + xfs_trans_brelse(ds->dargs.trans,
> > > + ds->state->altpath.blk[level].bp);
> > Indentation here (in xfs we use two spaces)
>
> Okay, I will fix this.
>
> >
> > Also, uh, shouldn't we set ds->state->altpath.blk[level].bp to NULL
> > since we've released the buffer?
>
> So I should set ds->state->altpath.blk[level].bp to NULL at the end of the
> function xchk_da_btree_block_check_sibling()?
> Like:
> ??? if (ds->state->altpath.blk[level].bp)
> ??????? xfs_trans_brelse(ds->dargs.trans,
> ??????????????? ds->state->altpath.blk[level].bp);
> ??? ds->state->altpath.blk[level].bp = NULL;

You could put the whole thing in a single if clause, e.g.

if (ds->state->altpath.blk[level].bp) {
xfs_trans_brelse(ds->dargs.trans,
ds->state->altpath.blk[level].bp);
ds->state->altpath.blk[level].bp = NULL;
}

--D

>
>
> Best wishes,
> Jia-Ju Bai