Re: [PATCH] radeon: avoid double free in ci_dpm_init()

[Alex Deucher]

On Wed, Apr 12, 2023 at 8:39 AM Nikita Zhandarovich
<n.zhandarovich@xxxxxxxxxx> wrote:
>
>
>
> On 4/11/23 14:11, Deucher, Alexander wrote:
> > [Public]
> >
> >> -----Original Message-----
> >> From: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
> >> Sent: Monday, April 3, 2023 2:28 PM
> >> To: Deucher, Alexander <Alexander.Deucher@xxxxxxx>
> >> Cc: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>; Koenig, Christian
> >> <Christian.Koenig@xxxxxxx>; Pan, Xinhui <Xinhui.Pan@xxxxxxx>; David
> >> Airlie <airlied@xxxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; amd-
> >> gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-
> >> kernel@xxxxxxxxxxxxxxx; lvc-project@xxxxxxxxxxxxxxxx
> >> Subject: [PATCH] radeon: avoid double free in ci_dpm_init()
> >>
> >> There are several calls to ci_dpm_fini() in ci_dpm_init() when there occur
> >> errors in functions like r600_parse_extended_power_table().
> >> This is harmful as it can lead to double free situations: for instance,
> >> r600_parse_extended_power_table() will call for
> >> r600_free_extended_power_table() as will ci_dpm_fini(), both of which will
> >> try to free resources.
> >> Other drivers do not call *_dpm_fini functions from their respective
> >> *_dpm_init calls - neither should cpm_dpm_init().
> >>
> >> Fix this by removing extra calls to ci_dpm_fini().
> >
> > You can't just drop the calls to fini().  You'll need to properly unwind to avoid leaking memory.
> >
> > Alex
> >>>
> >> Found by Linux Verification Center (linuxtesting.org) with static analysis tool
> >> SVACE.
> >>
> >> Fixes: cc8dbbb4f62a ("drm/radeon: add dpm support for CI dGPUs (v2)")
> >> Cc: stable@xxxxxxxxxxxxxxx
> >> Co-developed-by: Natalia Petrova <n.petrova@xxxxxxxxxx>
> >> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
> >>
> >> ---
> >>  drivers/gpu/drm/radeon/ci_dpm.c | 20 +++++---------------
> >>  1 file changed, 5 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/radeon/ci_dpm.c
> >> b/drivers/gpu/drm/radeon/ci_dpm.c index 8ef25ab305ae..7b77d4c93f1d
> >> 100644
> >> --- a/drivers/gpu/drm/radeon/ci_dpm.c
> >> +++ b/drivers/gpu/drm/radeon/ci_dpm.c
> >> @@ -5677,28 +5677,20 @@ int ci_dpm_init(struct radeon_device *rdev)
> >>      pi->pcie_lane_powersaving.min = 16;
> >>
> >>      ret = ci_get_vbios_boot_values(rdev, &pi->vbios_boot_state);
> >> -    if (ret) {
> >> -            ci_dpm_fini(rdev);
> >> +    if (ret)
> >>              return ret;
> >> -    }
> >>
> >>      ret = r600_get_platform_caps(rdev);
> >> -    if (ret) {
> >> -            ci_dpm_fini(rdev);
> >> +    if (ret)
> >>              return ret;
> >> -    }
> >>
> >>      ret = r600_parse_extended_power_table(rdev);
> >> -    if (ret) {
> >> -            ci_dpm_fini(rdev);
> >> +    if (ret)
> >>              return ret;
> >> -    }
> >>
> >>      ret = ci_parse_power_table(rdev);
> >> -    if (ret) {
> >> -            ci_dpm_fini(rdev);
> >> +    if (ret)
> >>              return ret;
> >> -    }
> >>
> >>      pi->dll_default_on = false;
> >>      pi->sram_end = SMC_RAM_END;
> >> @@ -5749,10 +5741,8 @@ int ci_dpm_init(struct radeon_device *rdev)
> >>              kcalloc(4,
> >>                      sizeof(struct
> >> radeon_clock_voltage_dependency_entry),
> >>                      GFP_KERNEL);
> >> -    if (!rdev-
> >>> pm.dpm.dyn_state.vddc_dependency_on_dispclk.entries) {
> >> -            ci_dpm_fini(rdev);
> >> +    if (!rdev-
> >>> pm.dpm.dyn_state.vddc_dependency_on_dispclk.entries)
> >>              return -ENOMEM;
> >> -    }
> >>      rdev->pm.dpm.dyn_state.vddc_dependency_on_dispclk.count = 4;
> >>      rdev-
> >>> pm.dpm.dyn_state.vddc_dependency_on_dispclk.entries[0].clk = 0;
> >>      rdev-
> >>> pm.dpm.dyn_state.vddc_dependency_on_dispclk.entries[0].v = 0;
>
>
> I think you are correct when it comes to ensuring we deal with memory
> issues in ci_dpm_init().
>
> However, I could use some direction on how to deal with the problem of
> freeing only previously allocated resources. For instance, once
> ci_parse_power_table() fails, it is not clear what we should and should
> not free.

You'll want to free any memory allocated in ci_dpm_init().  Any of the
functions called from that function should clean themselves up if they
allocate any memory, but if not, they should be fixed.

Alex


>
> I wanna point out that in this case I would like to fix both double and
> uninitialized free issues as it can also lead to undefined behavior.
>
> Thanks for your patience,
> Nikita