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Fri, 29 Nov 2019 20:03:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 02DF41138606; Fri, 29 Nov 2019 21:03:54 +0100 (CET) From: Markus Armbruster To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v6] hw/core/loader-fit: fix freeing errp in fit_load_fdt References: <20191127183016.13852-1-vsementsov@virtuozzo.com> <87muceeq5l.fsf@dusky.pond.sub.org> <4fcd8245-790e-220d-366b-ce25743dddc8@virtuozzo.com> <48c23c62-59ed-3da7-4803-cafd14b8fe49@virtuozzo.com> <87tv6mbta9.fsf@dusky.pond.sub.org> <988bff55-1f94-ac29-6193-7de13b2feca0@virtuozzo.com> Date: Fri, 29 Nov 2019 21:03:54 +0100 In-Reply-To: <988bff55-1f94-ac29-6193-7de13b2feca0@virtuozzo.com> (Vladimir Sementsov-Ogievskiy's message of "Fri, 29 Nov 2019 15:32:53 +0000") Message-ID: <874kymv49h.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: pBXU41WQOqu1HVOKS2aWvQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "pburton@wavecomp.com" , "aleksandar.rikalo@rt-rk.com" , "qemu-devel@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Vladimir Sementsov-Ogievskiy writes: > 29.11.2019 18:23, Markus Armbruster wrote: >> Vladimir Sementsov-Ogievskiy writes: >>=20 >>> 29.11.2019 17:11, Vladimir Sementsov-Ogievskiy wrote: >>>> 29.11.2019 17:03, Markus Armbruster wrote: >>>>> Vladimir Sementsov-Ogievskiy writes: >>>>> >>>>>> fit_load_fdt forget to check that errp is not NULL and to zero it af= ter >>>>>> freeing. Fix it. >>>>>> >>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>>>>> Reviewed-by: Eric Blake >>>>>> --- >>>>>> =C2=A0 hw/core/loader-fit.c | 5 ++++- >>>>>> =C2=A0 1 file changed, 4 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/hw/core/loader-fit.c b/hw/core/loader-fit.c >>>>>> index 953b16bc82..3ee9fb2f2e 100644 >>>>>> --- a/hw/core/loader-fit.c >>>>>> +++ b/hw/core/loader-fit.c >>>>>> @@ -200,7 +200,10 @@ static int fit_load_fdt(const struct fit_loader= *ldr, const void *itb, >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 err =3D fit_image_addr(itb, img_off,= "load", &load_addr, errp); >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (err =3D=3D -ENOENT) { >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 load_addr = =3D ROUND_UP(kernel_end, 64 * KiB) + (10 * MiB); >>>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 error_free(*errp); >>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (errp) { >>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = error_free(*errp); >>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 = *errp =3D NULL; >>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else if (err) { >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 error_prepen= d(errp, "unable to read FDT load address from FIT: "); >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D err; >>>>> >>>>> This fixes latent bugs when fit_image_addr() fails with ENOENT: >>>>> >>>>> * If a caller passes a null @errp, we crash dereferencing it >>>>> >>>>> * Else, we pass a dangling Error * to the caller, and return success. >>>>> =C2=A0=C2=A0 If a caller dereferences the Error * regardless, we hav= e a >>>>> =C2=A0=C2=A0 use-after-free. >>>>> >>>>> Not fixed: >>>>> >>>>> * If a caller passes &error_abort or &error_fatal, we die instead of >>>>> =C2=A0=C2=A0 taking the recovery path. >>>> >>>> No, if it is error_abort or error_fatal, we will not reach this point,= the execution >>>> finished before, when error was set. >>> >>> Ah, that is what you mention.. Hmm. Is it bad? At least crashing on >>> error_abort without any recovery should not be bad.. >>=20 >> Latent bugs aren't bad, but they could possibly become bad :) >>=20 >> When you pass &err to fit_load_fdt(), where @err is a local variable, >> the ENOENT case is not actually an error; fit_load_fdt() recovers fine >> and succeeds. >>=20 >> When you pass &error_fatal or &error_abort, it should likewise not be an >> error. > > Ah, yes, understand now. > > Interesting, that auto-propageted errp will not catch this. It will only > help with error_fatal, but not with error_abort.. > > So, in this case we should wrap error_abort too. And it in every function= that > uses error_free. > > And this means, that in this case we can't make error_abort crash at poin= t where > actual error occures. That is very sad. If your patches improve &error_abort's backtrace except for the (few) functions calling error_free(), then I'd call the situation "a bit sad" at most :) [...]