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[24.130.14.162]) by smtp.gmail.com with ESMTPSA id d21sm50304357pgv.37.2018.11.23.16.51.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 23 Nov 2018 16:51:51 -0800 (PST) Message-ID: <1543020709.12764.3.camel@dubeyko.com> Subject: Re: [PATCH] hfs: do not free node before using From: Viacheslav Dubeyko To: Pan Bian , Joe Perches , "Ernesto A." =?ISO-8859-1?Q?Fern=E1ndez?= , Andrew Morton Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 23 Nov 2018 16:51:49 -0800 In-Reply-To: <1542963889-128825-1-git-send-email-bianpan2016@163.com> References: <1542963889-128825-1-git-send-email-bianpan2016@163.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-11-23 at 17:04 +0800, Pan Bian wrote: > The function hfs_bmap_free frees node via hfs_bnode_put(node). > However, > it then reads node->this when dumping error message on an error path, > which may result in a use-after-free bug. This patch frees node only > when it is never used. > > Fixes: d614267329f("hfs/hfsplus: convert printks to pr_") > > Signed-off-by: Pan Bian > --- >  fs/hfs/btree.c | 3 ++- >  1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c > index 98b96ff..19017d2 100644 > --- a/fs/hfs/btree.c > +++ b/fs/hfs/btree.c > @@ -338,13 +338,14 @@ void hfs_bmap_free(struct hfs_bnode *node) >   >   nidx -= len * 8; >   i = node->next; > - hfs_bnode_put(node); >   if (!i) { >   /* panic */; >   pr_crit("unable to free bnode %u. bmap not > found!\n", >   node->this); What's about simply to store node->this into the local variable in the beginning of the cycle? In this case, it is possible to use the node ID in the pr_crit() and to use the hfs_bnode_put(node) in the same place without to use it twice. What do you think? Thanks, Vyacheslav Dubeyko. > + hfs_bnode_put(node); >   return; >   } > + hfs_bnode_put(node); >   node = hfs_bnode_find(tree, i); >   if (IS_ERR(node)) >   return;