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Date:   Tue, 5 Mar 2019 15:25:57 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] drm/vkms: fix use-after-free when drm_gem_handle_create() fails

On Tue, Mar 5, 2019 at 12:23 AM Rodrigo Siqueira
<rodrigosiqueiramelo@...il.com> wrote:
>
> On 02/28, Dmitry Vyukov wrote:
> > On Thu, Feb 28, 2019 at 12:12 AM Rodrigo Siqueira
> > <rodrigosiqueiramelo@...il.com> wrote:
> > >
> > > On 02/26, Eric Biggers wrote:
> > > > From: Eric Biggers <ebiggers@...gle.com>
> > > >
> > > > If drm_gem_handle_create() fails in vkms_gem_create(), then the
> > > > vkms_gem_object is freed twice: once when the reference is dropped by
> > > > drm_gem_object_put_unlocked(), and again by the extra calls to
> > > > drm_gem_object_release() and kfree().
> > > >
> > > > Fix it by skipping the second release and free.
> > > >
> > > > This bug was originally found in the vgem driver by syzkaller using
> > > > fault injection, but I noticed it's also present in the vkms driver.
> > > >
> > > > Fixes: 559e50fd34d1 ("drm/vkms: Add dumb operations")
> > > > Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> > > > Cc: Haneen Mohammed <hamohammed.sa@...il.com>
> > > > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > > > Cc: Chris Wilson <chris@...is-wilson.co.uk>
> > > > Cc: stable@...r.kernel.org
> > > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > > ---
> > > >  drivers/gpu/drm/vkms/vkms_gem.c | 5 +----
> > > >  1 file changed, 1 insertion(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
> > > > index 138b0bb325cf9..69048e73377dc 100644
> > > > --- a/drivers/gpu/drm/vkms/vkms_gem.c
> > > > +++ b/drivers/gpu/drm/vkms/vkms_gem.c
> > > > @@ -111,11 +111,8 @@ struct drm_gem_object *vkms_gem_create(struct drm_device *dev,
> > > >
> > > >       ret = drm_gem_handle_create(file, &obj->gem, handle);
> > > >       drm_gem_object_put_unlocked(&obj->gem);
> > > > -     if (ret) {
> > > > -             drm_gem_object_release(&obj->gem);
> > > > -             kfree(obj);
> > > > +     if (ret)
> > > >               return ERR_PTR(ret);
> > > > -     }
> > > >
> > > >       return &obj->gem;
> > > >  }
> > > > --
> > > > 2.21.0.rc2.261.ga7da99ff1b-goog
> > > >
> > >
> > > Hi,
> > >
> > > Thanks for your patch! :)
> > >
> > > The patch looks good for me. I also tested it under the IGT tests on my
> > > local VM and everything was fine.
>
> Hi,
>
> Patch applied to drm-misc-fixes.
>
> > Hi Rodrigo,
> >
> > What are IGT tests? How can I run them?
>
> Hi Dmitry,
>
> IGT is a test suite focused on DRM drivers.
>
> You can clone the project using the link below:
>
>   https://gitlab.freedesktop.org/drm/igt-gpu-tools.git
>
> In the README, you will find the software dependencies. After you
> install all the required package, just use:
>
>  mkdir build && meson build && cd build && ninja

Hi Rodrigo,

Thanks for the info, but this did not work for me.
I installed all recommended packages (including libdw-dev), but then got:

igt-gpu-tools$ mkdir -p build && meson build && cd build && ninja
The Meson build system
Version: 0.46.1
Source dir: /src/igt-gpu-tools
Build dir: /src/igt-gpu-tools/build
Build type: native build
Project name: igt-gpu-tools
Native C compiler: ccache cc (gcc 7.3.0 "cc (Debian 7.3.0-5) 7.3.0")
Build machine cpu family: x86_64
Build machine cpu: x86_64
Compiler for C supports arguments -Wbad-function-cast: YES
Compiler for C supports arguments -Wdeclaration-after-statement: YES
Compiler for C supports arguments -Wformat=2: YES
Compiler for C supports arguments -Wimplicit-fallthrough=0: YES
Compiler for C supports arguments -Wlogical-op: YES
Compiler for C supports arguments -Wmissing-declarations: YES
Compiler for C supports arguments -Wmissing-format-attribute: YES
Compiler for C supports arguments -Wmissing-noreturn: YES
Compiler for C supports arguments -Wmissing-prototypes: YES
Compiler for C supports arguments -Wnested-externs: YES
Compiler for C supports arguments -Wold-style-definition: YES
Compiler for C supports arguments -Wpointer-arith: YES
Compiler for C supports arguments -Wredundant-decls: YES
Compiler for C supports arguments -Wshadow: YES
Compiler for C supports arguments -Wstrict-prototypes: YES
Compiler for C supports arguments -Wuninitialized: YES
Compiler for C supports arguments -Wunused: YES
Compiler for C supports arguments -Wno-clobbered -Wclobbered: YES
Compiler for C supports arguments -Wno-maybe-uninitialized
-Wmaybe-uninitialized: YES
Compiler for C supports arguments -Wno-missing-field-initializers
-Wmissing-field-initializers: YES
Compiler for C supports arguments -Wno-pointer-arith -Wpointer-arith: YES
Compiler for C supports arguments -Wno-sign-compare -Wsign-compare: YES
Compiler for C supports arguments -Wno-type-limits -Wtype-limits: YES
Compiler for C supports arguments -Wno-unused-parameter -Wunused-parameter: YES
Compiler for C supports arguments -Wno-unused-result -Wunused-result: YES
Compiler for C supports arguments -Werror=address: YES
Compiler for C supports arguments -Werror=array-bounds: YES
Compiler for C supports arguments -Werror=implicit: YES
Compiler for C supports arguments -Werror=init-self: YES
Compiler for C supports arguments -Werror=int-to-pointer-cast: YES
Compiler for C supports arguments -Werror=main: YES
Compiler for C supports arguments -Werror=missing-braces: YES
Compiler for C supports arguments -Werror=nonnull: YES
Compiler for C supports arguments -Werror=pointer-to-int-cast: YES
Compiler for C supports arguments -Werror=return-type: YES
Compiler for C supports arguments -Werror=sequence-point: YES
Compiler for C supports arguments -Werror=trigraphs: YES
Compiler for C supports arguments -Werror=write-strings: YES
Found pkg-config: /usr/bin/pkg-config (0.29)
Native dependency libdrm found: YES 2.4.91
Native dependency libdrm_intel found: YES 2.4.91
Native dependency libdrm_nouveau found: YES 2.4.91
Native dependency libdrm_amdgpu found: YES 2.4.91
Native dependency pciaccess found: YES 0.13.4
Native dependency libkmod found: YES 24
Native dependency libprocps found: YES 3.3.15
Native dependency libunwind found: YES 1.21

meson.build:151:0: ERROR:  Could not generate cargs for libdw:

A full log can be found at /src/igt-gpu-tools/build/meson-logs/meson-log.txt


and meson-log.txt ends with:

Compiler for C supports arguments -Werror=write-strings: YES
Found pkg-config: /usr/bin/pkg-config (0.29)
Determining dependency 'libdrm' with pkg-config executable '/usr/bin/pkg-config'
Native dependency libdrm found: YES 2.4.91
Determining dependency 'libdrm_intel' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libdrm_intel found: YES 2.4.91
Determining dependency 'libdrm_nouveau' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libdrm_nouveau found: YES 2.4.91
Determining dependency 'libdrm_amdgpu' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libdrm_amdgpu found: YES 2.4.91
Determining dependency 'pciaccess' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency pciaccess found: YES 0.13.4
Determining dependency 'libkmod' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libkmod found: YES 24
Determining dependency 'libprocps' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libprocps found: YES 3.3.15
Determining dependency 'libunwind' with pkg-config executable
'/usr/bin/pkg-config'
Native dependency libunwind found: YES 1.21
Determining dependency 'libdw' with pkg-config executable '/usr/bin/pkg-config'

meson.build:151:0: ERROR:  Could not generate cargs for libdw:

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