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[76.119.149.155]) by smtp.gmail.com with ESMTPSA id c70sm20373613qke.109.2020.07.28.05.50.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jul 2020 05:50:23 -0700 (PDT) Date: Tue, 28 Jul 2020 08:50:21 -0400 From: Peilin Ye To: David Laight Cc: David Airlie , Daniel Vetter , Dan Carpenter , Arnd Bergmann , Greg Kroah-Hartman , "linux-kernel-mentees@lists.linuxfoundation.org" , "dri-devel@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" Subject: Re: [Linux-kernel-mentees] [PATCH v2] drm/bufs: Prevent kernel-infoleak in copy_one_buf() Message-ID: <20200728125021.GA409978@PWN> References: <20200728014343.341303-1-yepeilin.cs@gmail.com> <20200728115210.408486-1-yepeilin.cs@gmail.com> <3058d741282b463d8aa7c8aff62e4326@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3058d741282b463d8aa7c8aff62e4326@AcuMS.aculab.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 28, 2020 at 12:35:17PM +0000, David Laight wrote: > From: Peilin Ye > > Sent: 28 July 2020 12:52 > > Currently `struct drm_buf_desc` is defined as follows: > > > > struct drm_buf_desc { > > int count; > > int size; > > int low_mark; > > int high_mark; > > enum { > > _DRM_PAGE_ALIGN = 0x01, > > _DRM_AGP_BUFFER = 0x02, > > _DRM_SG_BUFFER = 0x04, > > _DRM_FB_BUFFER = 0x08, > > _DRM_PCI_BUFFER_RO = 0x10 > > } flags; > > unsigned long agp_start; > > }; > > > > copy_one_buf() is potentially copying uninitialized kernel stack memory > > to userspace, since the compiler may leave such "holes" (around `.flags` > > and `.agp_start` fields) in this statically allocated structure. Prevent > > it by initializing `v` with memset(). > > > > Cc: stable@vger.kernel.org > > Fixes: 5c7640ab6258 ("switch compat_drm_infobufs() to drm_ioctl_kernel()") > > Suggested-by: Dan Carpenter > > Acked-by: Arnd Bergmann > > Signed-off-by: Peilin Ye > > --- > > Change in v2: > > - Improve commit description. (Suggested by Arnd Bergmann > > ) > > > > drivers/gpu/drm/drm_bufs.c | 12 ++++++++---- > > 1 file changed, 8 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c > > index a0735fbc144b..f99cd4a3f951 100644 > > --- a/drivers/gpu/drm/drm_bufs.c > > +++ b/drivers/gpu/drm/drm_bufs.c > > @@ -1349,10 +1349,14 @@ static int copy_one_buf(void *data, int count, struct drm_buf_entry *from) > > { > > struct drm_buf_info *request = data; > > struct drm_buf_desc __user *to = &request->list[count]; > > - struct drm_buf_desc v = {.count = from->buf_count, > > - .size = from->buf_size, > > - .low_mark = from->low_mark, > > - .high_mark = from->high_mark}; > > + struct drm_buf_desc v; > > + > > + memset(&v, 0, sizeof(v)); > > + > > + v.count = from->buf_count; > > + v.size = from->buf_size; > > + v.low_mark = from->low_mark; > > + v.high_mark = from->high_mark; > > > > if (copy_to_user(to, &v, offsetof(struct drm_buf_desc, flags))) > > return -EFAULT; > > The memset() isn't needed. > The copy_to_user() stops after the 4 'int' values so no 'random' > kernel stack can get copied. You are right, I overlooked that. Thank you for pointing this out! Peilin Ye > Quite why it is 'right' to leave the remaining part of each > userspace structure unchanged is another matter. > > David. > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >