From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202502 header.b=FSNoG4Ss; dkim-atps=neutral Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by passt.top (Postfix) with ESMTPS id 655785A0008 for ; Fri, 04 Apr 2025 01:35:28 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202502; t=1743723325; bh=OZihjebg/vC+/QZOY9fdeL7nfdIg9D/kjcZ0R8sbfjg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=FSNoG4Ss/cUxcXBRlM4fPMlqNQzuHRjj3V1kh4lERlfJv2vDcw6iFzk5q3iu5weyt IbnWKPwsPh6Dv2EdT0gXo0/oWZ4m3EaYVTTANbuUcB5lHEegzibO1N7oJXbeppYjyD MVNeggLdqjBZ/DL8zMaY/Rx1mlCwMn3327NTM4MtQGA/Zoqc6Jj8Up0GKxUvIYj3Vy u+EVggJBrHPUjM4kMBrZTT2Dza5BRW8xxTWViMv8TTaWdOm2dhiWpFM4RJKVCrqhXo a6y0UHw6jAsp9Q/txmAqn/RncX7Y7X8Go6I7fEA6XIiYJZqj40ryqB23mH3KONGmcW pj/J5OwQL6j5g== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4ZTJ4s49Xtz4x3d; Fri, 4 Apr 2025 10:35:25 +1100 (AEDT) Date: Fri, 4 Apr 2025 10:34:40 +1100 From: David Gibson To: Stefano Brivio Subject: Re: [PATCH] passt-repair: Ensure that read buffer is NULL-terminated Message-ID: References: <20250403190443.1932107-1-sbrivio@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="fbZTr1JgKG3eW3sk" Content-Disposition: inline In-Reply-To: <20250403190443.1932107-1-sbrivio@redhat.com> Message-ID-Hash: 67ABVGQJ52PYWGDEF4VHM5XKKLF3I4IW X-Message-ID-Hash: 67ABVGQJ52PYWGDEF4VHM5XKKLF3I4IW X-MailFrom: dgibson@gandalf.ozlabs.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --fbZTr1JgKG3eW3sk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Apr 03, 2025 at 09:04:43PM +0200, Stefano Brivio wrote: > After 3d41e4d83895 ("passt-repair: Correct off-by-one error verifying > name"), Coverity Scan isn't convinced anymore about the fact that the > ev->name used in the snprintf() is NULL-terminated. Aww, man :( > It comes from a read() call, and read() of course doesn't terminate > it, but we already check that the byte at ev->len - 1 is a NULL > terminator, so this is actually a false positive. Indeed. I'm kind of baffled that it's able to reason it out with the off-by-one, but not without. > In any case, the logic ensuring that ev->name is NULL-terminated isn't > necessarily obvious, and additionally checking that the last byte in > the buffer we read is a NULL terminator is harmless, so do that > explicitly, even if it's redundant. >=20 > Signed-off-by: Stefano Brivio Vexing that it's necessary, but Reviewed-by: David Gibson > --- > passt-repair.c | 1 + > 1 file changed, 1 insertion(+) >=20 > diff --git a/passt-repair.c b/passt-repair.c > index 440c77a..256a8c9 100644 > --- a/passt-repair.c > +++ b/passt-repair.c > @@ -137,6 +137,7 @@ int main(int argc, char **argv) > fprintf(stderr, "inotify read: %i", errno); > _exit(1); > } > + buf[n - 1] =3D '\0'; > =20 > if (n < (ssize_t)sizeof(*ev)) { > fprintf(stderr, "Short inotify read: %zi", n); --=20 David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson --fbZTr1JgKG3eW3sk Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmfvGw8ACgkQzQJF27ox 2GcM1w/+LDJimjP3KKXsupM3D8pwQNKMM7z3X/hLShmH7TfgWFHCh1TOrkgKa7xW 3qU3m113Td4NnV0RDHDotPtpdkcojCWEwNORRWo+kGJeZYcXxQC7q+6jcyk9b4Ft Vs0hhl9qARaS+Po5rEGs+wRfpTl0tYY/udqaL0jKKoXOyubjyfysG1MGIu5/HqHW 3FTk+Kx7AwXsMmS8THrVlzxniFjkmuNm90fn23xJIV3+FvNUf9K+V3NnsscxhUAV ZyEIJ2rBrWB2FlGR+t7+PVAq0d6ldO9IIWmtR2x9iY6IbJzXfBqMyxGQ8KrUPfto WMqDED2ivynDU86vdcDmPhbv8gxA9dWrTe+OErO0eoshsUNxQsPZDsRPx4fpeETV gtzSreuzVdGhWmi5LWr26Q1KIklseFSGsgxpbJKiD8Ons+P+RTEaUV6b348s/sZh jOqfrzgDIh1L2Ct7/8zdwHEGipGaM/meZY2KsmF67qiJctIjaK25qCCVLn4x0iLq DxjnzXGLauyebFbG6kIIQZCDMo7qXjc0t37+nnuMN3Irms9D2Y3+/w+h9avbI/EW 36AtV5a7D5kDFMKnqxrq44s9/3+iIL426WYCumddEbgWj9ywBVUdP62h8wUk4Qco EoCvb9QzDa2fIDCc2gHUNAoJAkIYvqRebW1AScJUb8lMNQUJPx0= =mzHG -----END PGP SIGNATURE----- --fbZTr1JgKG3eW3sk--