Re: [Ocfs2-devel] [PATCH 1/3 v2] fs: ocfs2: Fix possible null-pointer dereferences in ocfs2_xa_prepare_entry()

[Changwei Ge]

Hi Jia-Ju,


Please checkout my comments inline.


On 2019/7/27 8:49 äå, Joseph Qi wrote:
> On 19/7/26 18:14, Jia-Ju Bai wrote:
> > In ocfs2_xa_prepare_entry(), there is an if statement on line 2136 to
> > check whether loc->xl_entry is NULL:
> >      if (loc->xl_entry)
> >
> > When loc->xl_entry is NULL, it is used on line 2158:
> >      ocfs2_xa_add_entry(loc, name_hash);

This won't deference a NULL ->xl_entry because ->xlo_add_entry() is 
already called to whether ocfs2_xa_block_add_entry() or 
ocfs2_xa_bucket_add_entry()

From the function name we can tell the intention it wants to add entry 
so of course it should be NULL before calling it.


Thanks,

Changwei


> >          loc->xl_entry->xe_name_hash = cpu_to_le32(name_hash);
> >          loc->xl_entry->xe_name_offset = cpu_to_le16(loc->xl_size);
> > and line 2164:
> >      ocfs2_xa_add_namevalue(loc, xi);
> >          loc->xl_entry->xe_value_size = cpu_to_le64(xi->xi_value_len);
> >          loc->xl_entry->xe_name_len = xi->xi_name_len;
> >
> > Thus, possible null-pointer dereferences may occur.
> >
> > To fix these bugs, if loc-xl_entry is NULL, ocfs2_xa_prepare_entry()
> > abnormally returns with -EINVAL.
> >
> > These bugs are found by a static analysis tool STCheck written by us.
> >
> > Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
> Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> > ---
> > v2:
> > * Directly return -EINVAL if loc-xl_entry is NULL.
> >    Thank Joseph for helpful advice.
> >
> > ---
> >   fs/ocfs2/xattr.c | 44 +++++++++++++++++++++++---------------------
> >   1 file changed, 23 insertions(+), 21 deletions(-)
> >
> > diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> > index 385f3aaa2448..4b876c82a35c 100644
> > --- a/fs/ocfs2/xattr.c
> > +++ b/fs/ocfs2/xattr.c
> > @@ -2133,29 +2133,31 @@ static int ocfs2_xa_prepare_entry(struct ocfs2_xa_loc *loc,
> >   	if (rc)
> >   		goto out;
> >   
> > -	if (loc->xl_entry) {
> > -		if (ocfs2_xa_can_reuse_entry(loc, xi)) {
> > -			orig_value_size = loc->xl_entry->xe_value_size;
> > -			rc = ocfs2_xa_reuse_entry(loc, xi, ctxt);
> > -			if (rc)
> > -				goto out;
> > -			goto alloc_value;
> > -		}
> > +	if (!loc->xl_entry) {
> > +		rc = -EINVAL;
> > +		goto out;
> > +	}
> >   
> > -		if (!ocfs2_xattr_is_local(loc->xl_entry)) {
> > -			orig_clusters = ocfs2_xa_value_clusters(loc);
> > -			rc = ocfs2_xa_value_truncate(loc, 0, ctxt);
> > -			if (rc) {
> > -				mlog_errno(rc);
> > -				ocfs2_xa_cleanup_value_truncate(loc,
> > -								"overwriting",
> > -								orig_clusters);
> > -				goto out;
> > -			}
> > +	if (ocfs2_xa_can_reuse_entry(loc, xi)) {
> > +		orig_value_size = loc->xl_entry->xe_value_size;
> > +		rc = ocfs2_xa_reuse_entry(loc, xi, ctxt);
> > +		if (rc)
> > +			goto out;
> > +		goto alloc_value;
> > +	}
> > +
> > +	if (!ocfs2_xattr_is_local(loc->xl_entry)) {
> > +		orig_clusters = ocfs2_xa_value_clusters(loc);
> > +		rc = ocfs2_xa_value_truncate(loc, 0, ctxt);
> > +		if (rc) {
> > +			mlog_errno(rc);
> > +			ocfs2_xa_cleanup_value_truncate(loc,
> > +							"overwriting",
> > +							orig_clusters);
> > +			goto out;
> >   		}
> > -		ocfs2_xa_wipe_namevalue(loc);
> > -	} else
> > -		ocfs2_xa_add_entry(loc, name_hash);
> > +	}
> > +	ocfs2_xa_wipe_namevalue(loc);
> >   
> >   	/*
> >   	 * If we get here, we have a blank entry.  Fill it.  We grow our
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