Hi Jaegeuk, > -----Original Message----- > From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx] > Sent: Saturday, July 05, 2014 2:43 PM > To: Chao Yu > Cc: Changman Lee; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [f2fs-dev][PATCH 1/2] f2fs: check name_len of dir entry to prevent from deadloop > > Hi Chao, > > On Wed, Jul 02, 2014 at 01:23:47PM +0800, Chao Yu wrote: > > We assume that modification of some special application could result in zeroed > > name_len, or it is consciously made by somebody. We will deadloop in > > find_in_block when name_len of dir entry is zero. > > Could you explain this a little bit more? > I'm not sure how it can happen. IMO, On one hand, programs like mkfs/fsck/img2simg and f2fs could directly operate the raw device, so bugs of these software may be triggered to generate the corrupt data such as zeroed name_len. On the other hand, it' could be treated as a potential security problem, because user could crafted such a malicious image include zeroed name_len for hacking purpose. Once such special image is being mounted, deadloop could be triggered, finally will result in effecting on linux system's running. Thanks, Yu > I think the zeroed name_len would cause some problems in f2fs_add_link. > > Thanks, > > > > > This patch is added for preventing deadloop in above scenario. > > > > Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx> > > --- > > fs/f2fs/dir.c | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c > > index be8c7af..4316ec5 100644 > > --- a/fs/f2fs/dir.c > > +++ b/fs/f2fs/dir.c > > @@ -121,6 +121,16 @@ static struct f2fs_dir_entry *find_in_block(struct page *dentry_page, > > } > > } > > > > + /* check name_len to prevent from deadloop here */ > > + if (unlikely(de->name_len == 0)) { > > + struct inode *inode = dentry_page->mapping->host; > > + > > + f2fs_msg(inode->i_sb, KERN_ERR, > > + "zero-length dir entry, ino = %lu, name = %s", > > + (unsigned long)inode->i_ino, name->name); > > + break; > > + } > > + > > bit_start = bit_pos > > + GET_DENTRY_SLOTS(le16_to_cpu(de->name_len)); > > } > > -- > > 1.7.9.5 > > -- > Jaegeuk Kim -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
