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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id az38-20020a05600c602600b003a0323463absm19478592wmb.45.2022.07.04.05.36.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Jul 2022 05:36:35 -0700 (PDT) Message-ID: <8e783b8c-e7b9-3d8e-e80d-2f2608421293@redhat.com> Date: Mon, 4 Jul 2022 14:36:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 2/2] drm: Prevent drm_copy_field() to attempt copying a NULL pointer Content-Language: en-US To: Thomas Zimmermann , linux-kernel@vger.kernel.org Cc: David Airlie , dri-devel@lists.freedesktop.org, Peter Robinson References: <20220701120755.2135100-1-javierm@redhat.com> <20220701120755.2135100-3-javierm@redhat.com> From: Javier Martinez Canillas In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Thomas, Thanks for your feedback. On 7/4/22 14:30, Thomas Zimmermann wrote: > Hi > > Am 01.07.22 um 14:07 schrieb Javier Martinez Canillas: >> The drm_copy_field() helper is used to copy some struct drm_driver fields >> to userspace through the DRM_IOCTL_VERSION ioctl. But it could be possible >> that the driver didn't set some of the fields and are instead set to NULL. >> >> If that is the case, the drm_copy_field() attempts to copy a NULL pointer: >> >> [ +10.395966] Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000000 >> [ +0.010955] Mem abort info: >> [ +0.002835] ESR = 0x0000000096000004 >> [ +0.003872] EC = 0x25: DABT (current EL), IL = 32 bits >> [ +0.005395] SET = 0, FnV = 0 >> [ +0.003113] EA = 0, S1PTW = 0 >> [ +0.003182] FSC = 0x04: level 0 translation fault >> [ +0.004964] Data abort info: >> [ +0.002919] ISV = 0, ISS = 0x00000004 >> [ +0.003886] CM = 0, WnR = 0 >> [ +0.003040] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000115dad000 >> [ +0.006536] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000 >> [ +0.006925] Internal error: Oops: 96000004 [#1] SMP >> ... >> [ +0.011113] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> [ +0.007061] pc : __pi_strlen+0x14/0x150 >> [ +0.003895] lr : drm_copy_field+0x30/0x1a4 >> [ +0.004156] sp : ffff8000094b3a50 >> [ +0.003355] x29: ffff8000094b3a50 x28: ffff8000094b3b70 x27: 0000000000000040 >> [ +0.007242] x26: ffff443743c2ba00 x25: 0000000000000000 x24: 0000000000000040 >> [ +0.007243] x23: ffff443743c2ba00 x22: ffff8000094b3b70 x21: 0000000000000000 >> [ +0.007241] x20: 0000000000000000 x19: ffff8000094b3b90 x18: 0000000000000000 >> [ +0.007241] x17: 0000000000000000 x16: 0000000000000000 x15: 0000aaab14b9af40 >> [ +0.007241] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 >> [ +0.007239] x11: 0000000000000000 x10: 0000000000000000 x9 : ffffa524ad67d4d8 >> [ +0.007242] x8 : 0101010101010101 x7 : 7f7f7f7f7f7f7f7f x6 : 6c6e6263606e7141 >> [ +0.007239] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000 >> [ +0.007241] x2 : 0000000000000000 x1 : ffff8000094b3b90 x0 : 0000000000000000 >> [ +0.007240] Call trace: >> [ +0.002475] __pi_strlen+0x14/0x150 >> [ +0.003537] drm_version+0x84/0xac >> [ +0.003448] drm_ioctl_kernel+0xa8/0x16c >> [ +0.003975] drm_ioctl+0x270/0x580 >> [ +0.003448] __arm64_sys_ioctl+0xb8/0xfc >> [ +0.003978] invoke_syscall+0x78/0x100 >> [ +0.003799] el0_svc_common.constprop.0+0x4c/0xf4 >> [ +0.004767] do_el0_svc+0x38/0x4c >> [ +0.003357] el0_svc+0x34/0x100 >> [ +0.003185] el0t_64_sync_handler+0x11c/0x150 >> [ +0.004418] el0t_64_sync+0x190/0x194 >> [ +0.003716] Code: 92402c04 b200c3e8 f13fc09f 5400088c (a9400c02) >> [ +0.006180] ---[ end trace 0000000000000000 ]--- >> >> Reported-by: Peter Robinson >> Signed-off-by: Javier Martinez Canillas >> --- >> >> drivers/gpu/drm/drm_ioctl.c | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c >> index e1b9a03e619c..dacaddc59c82 100644 >> --- a/drivers/gpu/drm/drm_ioctl.c >> +++ b/drivers/gpu/drm/drm_ioctl.c >> @@ -474,6 +474,10 @@ static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value) >> { >> size_t len; >> >> + /* don't attempt to copy a NULL pointer */ >> + if (WARN_ONCE(!value, "BUG: the value to copy was not set!")) >> + return -EINVAL; >> + > > We usually assume that the caller passes the correct arguments. This is > different for no reasons. I'd rather not take this patch unless there's > a security implication to the ioctl interface (e.g., leaking information > because of this NULL ptr). > This can lead from an oops (soft panic) to a kernel crash for a buggy driver. I see from where you are coming from but then I think we should sanitize the filled struct drm_driver fields in drm_dev_register() and make it fail early. Would you agree with such a patch? But what I think that we shouldn't allow is to attempt copying a NULL pointer, if we can easily prevent it. -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat