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Mon, 02 Mar 2020 07:38:25 -0800 (PST) Subject: Re: [PATCH] scsi/qemu-pr-helper: Fix out-of-bounds access to trnptid_list[] To: Christophe de Dinechin , qemu-devel@nongnu.org References: <20200228150059.2644362-1-dinechin@redhat.com> From: Paolo Bonzini Message-ID: Date: Mon, 2 Mar 2020 16:38:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200228150059.2644362-1-dinechin@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com 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] 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: Fam Zheng , qemu-stable , qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 28/02/20 16:00, Christophe de Dinechin wrote: > Compile error reported by gcc 10.0.1: >=20 > scsi/qemu-pr-helper.c: In function =E2=80=98multipath_pr_out=E2=80=99: > scsi/qemu-pr-helper.c:523:32: error: array subscript is outside= array bounds of =E2=80=98struct transportid *[0]=E2=80=99 [-Werror=3Darray= -bounds] > 523 | paramp.trnptid_list[paramp.num_transportid++] =3D id; > | ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~ > In file included from scsi/qemu-pr-helper.c:36: > /usr/include/mpath_persist.h:168:22: note: while referencing =E2=80=98trn= ptid_list=E2=80=99 > 168 | struct transportid *trnptid_list[]; > | ^~~~~~~~~~~~ > scsi/qemu-pr-helper.c:424:35: note: defined here =E2=80=98paramp=E2=80=99 > 424 | struct prout_param_descriptor paramp; > | ^~~~~~ Ouch. Very nice new warning. Cc: qemu-stable@nongnu.org Queued, thanks. > This highlights an actual implementation issue in function multipath_pr_o= ut. > The variable paramp is declared with type `struct prout_param_descriptor`= , > which is a struct terminated by an empty array in mpath_persist.h: >=20 > struct transportid *trnptid_list[]; >=20 > That empty array was filled with code that looked like that: >=20 > trnptid_list[paramp.descr.num_transportid++] =3D id; >=20 > This is an actual out-of-bounds access. >=20 > The fix is to replace `paramp` with an anonymous struct that adds > additional space for the data, called `trnptid_list_storage`. > That space provides MATH_MX_TIDS entries, and is not accessed directly > but through a pointer to `descr.trnptid_list`, in the unlikely case a > future compiler inserts some padding between the two structs. >=20 > Signed-off-by: Christophe de Dinechin > --- > scsi/qemu-pr-helper.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) >=20 > diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c > index 0659ceef09..01013221b3 100644 > --- a/scsi/qemu-pr-helper.c > +++ b/scsi/qemu-pr-helper.c > @@ -421,7 +421,12 @@ static int multipath_pr_out(int fd, const uint8_t *c= db, uint8_t *sense, > int rq_servact =3D cdb[1]; > int rq_scope =3D cdb[2] >> 4; > int rq_type =3D cdb[2] & 0xf; > - struct prout_param_descriptor paramp; > + struct > + { > + struct prout_param_descriptor descr; > + struct transportid *trnptid_list_storage[MPATH_MX_TIDS]; > + } paramp; > + struct transportid **trnptid_list =3D paramp.descr.trnptid_list; > char transportids[PR_HELPER_DATA_SIZE]; > int r; > =20 > @@ -455,9 +460,9 @@ static int multipath_pr_out(int fd, const uint8_t *cd= b, uint8_t *sense, > * do the opposite). > */ > memset(¶mp, 0, sizeof(paramp)); > - memcpy(¶mp.key, ¶m[0], 8); > - memcpy(¶mp.sa_key, ¶m[8], 8); > - paramp.sa_flags =3D param[20]; > + memcpy(¶mp.descr.key, ¶m[0], 8); > + memcpy(¶mp.descr.sa_key, ¶m[8], 8); > + paramp.descr.sa_flags =3D param[20]; > if (sz > PR_OUT_FIXED_PARAM_SIZE) { > size_t transportid_len; > int i, j; > @@ -520,12 +525,13 @@ static int multipath_pr_out(int fd, const uint8_t *= cdb, uint8_t *sense, > return CHECK_CONDITION; > } > =20 > - paramp.trnptid_list[paramp.num_transportid++] =3D id; > + assert(paramp.descr.num_transportid < MPATH_MX_TIDS); > + trnptid_list[paramp.descr.num_transportid++] =3D id; > } > } > =20 > r =3D mpath_persistent_reserve_out(fd, rq_servact, rq_scope, rq_type= , > - ¶mp, noisy, verbose); > + ¶mp.descr, noisy, verbose); > return mpath_reconstruct_sense(fd, r, sense); > } > #endif >=20