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Fri, 29 Nov 2019 15:23:43 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 44D591138606; Fri, 29 Nov 2019 16:23:42 +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> Date: Fri, 29 Nov 2019 16:23:42 +0100 In-Reply-To: <48c23c62-59ed-3da7-4803-cafd14b8fe49@virtuozzo.com> (Vladimir Sementsov-Ogievskiy's message of "Fri, 29 Nov 2019 14:12:33 +0000") Message-ID: <87tv6mbta9.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 10.5.11.15 X-MC-Unique: xkiqddR3O5eqD5mo4jcjHA-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: 207.211.31.120 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 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 afte= r >>>> 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, "l= oad", &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 R= OUND_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 er= ror_free(*errp); >>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 *e= rrp =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_prepend(e= rrp, "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 have 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. >>=20 >> No, if it is error_abort or error_fatal, we will not reach this point, t= he 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.. Latent bugs aren't bad, but they could possibly become bad :) 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. When you pass &error_fatal or &error_abort, it should likewise not be an error. General rule: when you want to handle some (or all) of a function's errors yourself, you must not pass your own @errp argument. Instead, pass &err and propagate the errors you don't handle yourself with error_propagate(errp, err). >>> We need to use a local_err here. >>> >>> I'll search for the pattern, and post fix(es). Found several bugs already...