From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54205) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1er2Cj-0008Kv-8r for qemu-devel@nongnu.org; Wed, 28 Feb 2018 08:55:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1er2Ci-0004Rs-8y for qemu-devel@nongnu.org; Wed, 28 Feb 2018 08:55:33 -0500 References: <20180228131315.30194-1-mreitz@redhat.com> <20180228131315.30194-2-mreitz@redhat.com> <20180228133434.GL17774@redhat.com> <1fc55643-7ca6-26a5-7e2e-7d6b09a43a13@redhat.com> <20180228135305.GM17774@redhat.com> From: Max Reitz Message-ID: <86d7e709-6981-822d-9849-7af38e7453ce@redhat.com> Date: Wed, 28 Feb 2018 14:55:22 +0100 MIME-Version: 1.0 In-Reply-To: <20180228135305.GM17774@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="6Z8Cy0IBQAIiwSXsr1Fl3yZ43wWG9s1fj" Subject: Re: [Qemu-devel] [PATCH 1/2] block/file-posix: Fix fully preallocated truncate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, "eblake@redhat.com Kevin Wolf" , qemu-stable@nongnu.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --6Z8Cy0IBQAIiwSXsr1Fl3yZ43wWG9s1fj From: Max Reitz To: =?UTF-8?Q?Daniel_P._Berrang=c3=a9?= Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, "eblake@redhat.com Kevin Wolf" , qemu-stable@nongnu.org Message-ID: <86d7e709-6981-822d-9849-7af38e7453ce@redhat.com> Subject: Re: [PATCH 1/2] block/file-posix: Fix fully preallocated truncate References: <20180228131315.30194-1-mreitz@redhat.com> <20180228131315.30194-2-mreitz@redhat.com> <20180228133434.GL17774@redhat.com> <1fc55643-7ca6-26a5-7e2e-7d6b09a43a13@redhat.com> <20180228135305.GM17774@redhat.com> In-Reply-To: <20180228135305.GM17774@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 2018-02-28 14:53, Daniel P. Berrang=C3=A9 wrote: > On Wed, Feb 28, 2018 at 02:45:49PM +0100, Max Reitz wrote: >> On 2018-02-28 14:34, Daniel P. Berrang=C3=A9 wrote: >>> On Wed, Feb 28, 2018 at 02:13:14PM +0100, Max Reitz wrote: >>>> Storing the lseek() result in an int results in it overflowing when = the >>>> file is at least 2 GB big. Then, we have a 50 % chance of the resul= t >>>> being "negative" and thus thinking an error occurred when actually >>>> everything went just fine. >>>> >>>> So we should use the correct type for storing the result: off_t. >>>> >>>> Reported-by: Daniel P. Berrange >>>> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=3D1549231 >>>> Cc: qemu-stable@nongnu.org >>>> Signed-off-by: Max Reitz >>>> --- >>>> block/file-posix.c | 5 +++-- >>>> 1 file changed, 3 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/block/file-posix.c b/block/file-posix.c >>>> index f1591c3849..90c25864a0 100644 >>>> --- a/block/file-posix.c >>>> +++ b/block/file-posix.c >>>> @@ -1697,6 +1697,7 @@ static int raw_regular_truncate(int fd, int64_= t offset, PreallocMode prealloc, >>>> case PREALLOC_MODE_FULL: >>>> { >>>> int64_t num =3D 0, left =3D offset - current_length; >>>> + off_t seek_result; >>>> =20 >>>> /* >>>> * Knowing the final size from the beginning could allow th= e file >>>> @@ -1711,8 +1712,8 @@ static int raw_regular_truncate(int fd, int64_= t offset, PreallocMode prealloc, >>>> =20 >>>> buf =3D g_malloc0(65536); >>>> =20 >>>> - result =3D lseek(fd, current_length, SEEK_SET); >>>> - if (result < 0) { >>>> + seek_result =3D lseek(fd, current_length, SEEK_SET); >>>> + if (seek_result < 0) { >>> >>> off_t is an unsigned type, so this comparison to "< 0" is bogus - onl= y the >>> exact value (off_t)-1 indicates an error. So this needs to be >>> >>> if (seek_result =3D=3D (off_t)-1) { >>> ... >>> } >> >> Hmmm... On my system, it appears to be a long int[1]. And >> find_allocation() does an off_t < 0 comparison already. And >> "man 0p sys_types.h" says "blkcnt_t and off_t shall be signed integer >> types." >=20 > Hmm, that's odd then - lseek man page explicitly said it must be cast, > which suggested to me it could be unsigned: >=20 > RETURN VALUE > Upon successful completion, lseek() returns the resulting offset= loca=E2=80=90 > tion as measured in bytes from the beginning of the file. On= error, > the value (off_t) -1 is returned and errno is set to indica= te the > error. >=20 > CC'ing Eric for the "official" POSIX answer.... But it also says (under NOTES): The off_t data type is a signed integer data type specified by POSIX.1. Max --6Z8Cy0IBQAIiwSXsr1Fl3yZ43wWG9s1fj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQFGBAEBCAAwFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAlqWtMoSHG1yZWl0ekBy ZWRoYXQuY29tAAoJEPQH2wBh1c9AhmQH/jePXypviRVuF1mKw9hdcgZaK5YquGai uZrgB6oymBjfWA75Hp85r+28o/+DbN1d17OaIL5OJ2zjfxAZ6x9i03Ky55V+evQp FhxXaD+lrvS2sfQJGf9T8RkCtdIPuberuifJ518yunUKL5VRhpLEihySKtHUD0rY W8+kwS4yCMn2aE29Fcatzie5xNdm41AmOHa8mZ5VQb5jETCU0fT4E/xrcW8a4XCc a2OWdu4Ccl8YlEqcpM+FujYHReWCQDU4OvP5nE5/B7LTKk8i8FSJDTliIngaDLoH fmXPf7ihG4XZWwOlJvb5awbWR/UXgyadcQheA5m/lcJu2lyuCyEPkRU= =B5Ja -----END PGP SIGNATURE----- --6Z8Cy0IBQAIiwSXsr1Fl3yZ43wWG9s1fj--