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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id r14sm345587pjz.43.2021.04.19.14.42.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Apr 2021 14:42:14 -0700 (PDT) Date: Mon, 19 Apr 2021 14:42:13 -0700 From: Kees Cook To: Dan Carpenter Cc: Stefan Richter , Luo Likang , security@kernel.org, linux-distros@vs.openwall.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux1394-devel@lists.sourceforge.net Subject: Re: [PATCH] media: firewire: firedtv-avc: fix a buffer overflow in avc_ca_pmt() Message-ID: <202104191438.D54A181@keescook> References: <000001d73031$d5304480$7f90cd80$@nsfocus.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Wed, Apr 14, 2021 at 11:57:59AM +0300, Dan Carpenter wrote: > The bounds checking in avc_ca_pmt() is not strict enough. It should > be checking "read_pos + 4" because it's reading 5 bytes. If the > "es_info_length" is non-zero then it reads a 6th byte so there needs to > be an additional check for that. > > I also added checks for the "write_pos". I don't think these are > required because "read_pos" and "write_pos" are tied together so > checking one ought to be enough. But they make the code easier to > understand for me. > > The other problem is that "length" can be invalid. It comes from > "data_length" in fdtv_ca_pmt(). > > Cc: stable@vger.kernel.org > Reported-by: Luo Likang > Signed-off-by: Dan Carpenter Thanks for the report and the fix! As a quick note on alternative mitigations, it seems that CONFIG_UBSAN_BOUNDS would have caught this at runtime too. (i.e. c->operand[]'s size is known at build time, so out of bounds indexing should be detected.) -Kees > --- > This hardware isn't super common so there is no embargo. Resending > through normal lists. > > Oh, another thing is the data_length calculation in fdtv_ca_pmt() seems > very suspicous. Reading more than 4 bytes in the loop will lead to > shift wrapping. > > drivers/media/firewire/firedtv-avc.c | 14 +++++++++++--- > drivers/media/firewire/firedtv-ci.c | 2 ++ > 2 files changed, 13 insertions(+), 3 deletions(-) > > diff --git a/drivers/media/firewire/firedtv-avc.c b/drivers/media/firewire/firedtv-avc.c > index 2bf9467b917d..71991f8638e6 100644 > --- a/drivers/media/firewire/firedtv-avc.c > +++ b/drivers/media/firewire/firedtv-avc.c > @@ -1165,7 +1165,11 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length) > read_pos += program_info_length; > write_pos += program_info_length; > } > - while (read_pos < length) { > + while (read_pos + 4 < length) { > + if (write_pos + 4 >= sizeof(c->operand) - 4) { > + ret = -EINVAL; > + goto out; > + } > c->operand[write_pos++] = msg[read_pos++]; > c->operand[write_pos++] = msg[read_pos++]; > c->operand[write_pos++] = msg[read_pos++]; > @@ -1177,13 +1181,17 @@ int avc_ca_pmt(struct firedtv *fdtv, char *msg, int length) > c->operand[write_pos++] = es_info_length >> 8; > c->operand[write_pos++] = es_info_length & 0xff; > if (es_info_length > 0) { > + if (read_pos >= length) { > + ret = -EINVAL; > + goto out; > + } > pmt_cmd_id = msg[read_pos++]; > if (pmt_cmd_id != 1 && pmt_cmd_id != 4) > dev_err(fdtv->device, "invalid pmt_cmd_id %d at stream level\n", > pmt_cmd_id); > > - if (es_info_length > sizeof(c->operand) - 4 - > - write_pos) { > + if (es_info_length > sizeof(c->operand) - 4 - write_pos || > + es_info_length > length - read_pos) { > ret = -EINVAL; > goto out; > } > diff --git a/drivers/media/firewire/firedtv-ci.c b/drivers/media/firewire/firedtv-ci.c > index 9363d005e2b6..2d6992ac5dd6 100644 > --- a/drivers/media/firewire/firedtv-ci.c > +++ b/drivers/media/firewire/firedtv-ci.c > @@ -134,6 +134,8 @@ static int fdtv_ca_pmt(struct firedtv *fdtv, void *arg) > } else { > data_length = msg->msg[3]; > } > + if (data_length > sizeof(msg->msg) - 4) > + return -EINVAL; > > return avc_ca_pmt(fdtv, &msg->msg[data_pos], data_length); > } > -- > 2.30.2 > -- Kees Cook