[PATCH] cdrom: Make device operations read-only

From: Kees Cook
Date: Mon Feb 13 2017 - 19:25:39 EST

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Since function tables are a common target for attackers, it's best to keep
them in read-only memory. As such, this makes the CDROM device ops tables
const. This drops additionally n_minors, since it isn't used meaningfully,
and sets the only user of cdrom_dummy_generic_packet explicitly so the
variables can all be const.

Inspired by similar changes in grsecurity/PaX.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Documentation/cdrom/cdrom-standard.tex | 9 +-----
drivers/block/paride/pcd.c | 2 +-
drivers/cdrom/cdrom.c | 58 ++++++++++++++++------------------
drivers/cdrom/gdrom.c | 4 +--
drivers/ide/ide-cd.c | 2 +-
drivers/scsi/sr.c | 2 +-
include/linux/cdrom.h | 5 +--
7 files changed, 37 insertions(+), 45 deletions(-)

diff --git a/Documentation/cdrom/cdrom-standard.tex b/Documentation/cdrom/cdrom-standard.tex
index c06233fe52ac..8f85b0e41046 100644
--- a/Documentation/cdrom/cdrom-standard.tex
+++ b/Documentation/cdrom/cdrom-standard.tex
@@ -249,7 +249,6 @@ struct& cdrom_device_ops\ \{ \hidewidth\cr
unsigned\ long);\cr
\noalign{\medskip}
&const\ int& capability;& capability flags \cr
- &int& n_minors;& number of active minor devices \cr
\};\cr
}
$$
@@ -258,13 +257,7 @@ it should add a function pointer to this $struct$. When a particular
function is not implemented, however, this $struct$ should contain a
NULL instead. The $capability$ flags specify the capabilities of the
\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
-is registered with the \UCD. The value $n_minors$ should be a positive
-value indicating the number of minor devices that are supported by
-the low-level device driver, normally~1. Although these two variables
-are `informative' rather than `operational,' they are included in
-$cdrom_device_ops$ because they describe the capability of the {\em
-driver\/} rather than the {\em drive}. Nomenclature has always been
-difficult in computer programming.
+is registered with the \UCD.

Note that most functions have fewer parameters than their
$blkdev_fops$ counterparts. This is because very little of the
diff --git a/drivers/block/paride/pcd.c b/drivers/block/paride/pcd.c
index 5fd2d0e25567..10aed84244f5 100644
--- a/drivers/block/paride/pcd.c
+++ b/drivers/block/paride/pcd.c
@@ -273,7 +273,7 @@ static const struct block_device_operations pcd_bdops = {
.check_events = pcd_block_check_events,
};

-static struct cdrom_device_ops pcd_dops = {
+static const struct cdrom_device_ops pcd_dops = {
.open = pcd_open,
.release = pcd_release,
.drive_status = pcd_drive_status,
diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 59cca72647a6..bbbd3caa927c 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -342,8 +342,8 @@ static void cdrom_sysctl_register(void);

static LIST_HEAD(cdrom_list);

-static int cdrom_dummy_generic_packet(struct cdrom_device_info *cdi,
- struct packet_command *cgc)
+int cdrom_dummy_generic_packet(struct cdrom_device_info *cdi,
+ struct packet_command *cgc)
{
if (cgc->sense) {
cgc->sense->sense_key = 0x05;
@@ -354,6 +354,7 @@ static int cdrom_dummy_generic_packet(struct cdrom_device_info *cdi,
cgc->stat = -EIO;
return -EIO;
}
+EXPORT_SYMBOL(cdrom_dummy_generic_packet);

static int cdrom_flush_cache(struct cdrom_device_info *cdi)
{
@@ -371,7 +372,7 @@ static int cdrom_flush_cache(struct cdrom_device_info *cdi)
static int cdrom_get_disc_info(struct cdrom_device_info *cdi,
disc_information *di)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct packet_command cgc;
int ret, buflen;

@@ -586,7 +587,7 @@ static int cdrom_mrw_set_lba_space(struct cdrom_device_info *cdi, int space)
int register_cdrom(struct cdrom_device_info *cdi)
{
static char banner_printed;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
int *change_capability = (int *)&cdo->capability; /* hack */

cd_dbg(CD_OPEN, "entering register_cdrom\n");
@@ -610,7 +611,6 @@ int register_cdrom(struct cdrom_device_info *cdi)
ENSURE(reset, CDC_RESET);
ENSURE(generic_packet, CDC_GENERIC_PACKET);
cdi->mc_flags = 0;
- cdo->n_minors = 0;
cdi->options = CDO_USE_FFLAGS;

if (autoclose == 1 && CDROM_CAN(CDC_CLOSE_TRAY))
@@ -630,8 +630,7 @@ int register_cdrom(struct cdrom_device_info *cdi)
else
cdi->cdda_method = CDDA_OLD;

- if (!cdo->generic_packet)
- cdo->generic_packet = cdrom_dummy_generic_packet;
+ WARN_ON(!cdo->generic_packet);

cd_dbg(CD_REG_UNREG, "drive \"/dev/%s\" registered\n", cdi->name);
mutex_lock(&cdrom_mutex);
@@ -652,7 +651,6 @@ void unregister_cdrom(struct cdrom_device_info *cdi)
if (cdi->exit)
cdi->exit(cdi);

- cdi->ops->n_minors--;
cd_dbg(CD_REG_UNREG, "drive \"/dev/%s\" unregistered\n", cdi->name);
}

@@ -1036,7 +1034,7 @@ static
int open_for_data(struct cdrom_device_info *cdi)
{
int ret;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
tracktype tracks;
cd_dbg(CD_OPEN, "entering open_for_data\n");
/* Check if the driver can report drive status. If it can, we
@@ -1198,8 +1196,8 @@ int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev,
/* This code is similar to that in open_for_data. The routine is called
whenever an audio play operation is requested.
*/
-static int check_for_audio_disc(struct cdrom_device_info * cdi,
- struct cdrom_device_ops * cdo)
+static int check_for_audio_disc(struct cdrom_device_info *cdi,
+ const struct cdrom_device_ops *cdo)
{
int ret;
tracktype tracks;
@@ -1254,7 +1252,7 @@ static int check_for_audio_disc(struct cdrom_device_info * cdi,

void cdrom_release(struct cdrom_device_info *cdi, fmode_t mode)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
int opened_for_data;

cd_dbg(CD_CLOSE, "entering cdrom_release\n");
@@ -1294,7 +1292,7 @@ static int cdrom_read_mech_status(struct cdrom_device_info *cdi,
struct cdrom_changer_info *buf)
{
struct packet_command cgc;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
int length;

/*
@@ -1643,7 +1641,7 @@ static int dvd_do_auth(struct cdrom_device_info *cdi, dvd_authinfo *ai)
int ret;
u_char buf[20];
struct packet_command cgc;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
rpc_state_t rpc_state;

memset(buf, 0, sizeof(buf));
@@ -1791,7 +1789,7 @@ static int dvd_read_physical(struct cdrom_device_info *cdi, dvd_struct *s,
{
unsigned char buf[21], *base;
struct dvd_layer *layer;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
int ret, layer_num = s->physical.layer_num;

if (layer_num >= DVD_LAYERS)
@@ -1842,7 +1840,7 @@ static int dvd_read_copyright(struct cdrom_device_info *cdi, dvd_struct *s,
{
int ret;
u_char buf[8];
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

init_cdrom_command(cgc, buf, sizeof(buf), CGC_DATA_READ);
cgc->cmd[0] = GPCMD_READ_DVD_STRUCTURE;
@@ -1866,7 +1864,7 @@ static int dvd_read_disckey(struct cdrom_device_info *cdi, dvd_struct *s,
{
int ret, size;
u_char *buf;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

size = sizeof(s->disckey.value) + 4;

@@ -1894,7 +1892,7 @@ static int dvd_read_bca(struct cdrom_device_info *cdi, dvd_struct *s,
{
int ret, size = 4 + 188;
u_char *buf;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

buf = kmalloc(size, GFP_KERNEL);
if (!buf)
@@ -1928,7 +1926,7 @@ static int dvd_read_manufact(struct cdrom_device_info *cdi, dvd_struct *s,
{
int ret = 0, size;
u_char *buf;
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

size = sizeof(s->manufact.value) + 4;

@@ -1995,7 +1993,7 @@ int cdrom_mode_sense(struct cdrom_device_info *cdi,
struct packet_command *cgc,
int page_code, int page_control)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

memset(cgc->cmd, 0, sizeof(cgc->cmd));

@@ -2010,7 +2008,7 @@ int cdrom_mode_sense(struct cdrom_device_info *cdi,
int cdrom_mode_select(struct cdrom_device_info *cdi,
struct packet_command *cgc)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

memset(cgc->cmd, 0, sizeof(cgc->cmd));
memset(cgc->buffer, 0, 2);
@@ -2025,7 +2023,7 @@ int cdrom_mode_select(struct cdrom_device_info *cdi,
static int cdrom_read_subchannel(struct cdrom_device_info *cdi,
struct cdrom_subchnl *subchnl, int mcn)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct packet_command cgc;
char buffer[32];
int ret;
@@ -2073,7 +2071,7 @@ static int cdrom_read_cd(struct cdrom_device_info *cdi,
struct packet_command *cgc, int lba,
int blocksize, int nblocks)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

memset(&cgc->cmd, 0, sizeof(cgc->cmd));
cgc->cmd[0] = GPCMD_READ_10;
@@ -2093,7 +2091,7 @@ static int cdrom_read_block(struct cdrom_device_info *cdi,
struct packet_command *cgc,
int lba, int nblocks, int format, int blksize)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;

memset(&cgc->cmd, 0, sizeof(cgc->cmd));
cgc->cmd[0] = GPCMD_READ_CD;
@@ -2764,7 +2762,7 @@ static int cdrom_ioctl_audioctl(struct cdrom_device_info *cdi,
*/
static int cdrom_switch_blocksize(struct cdrom_device_info *cdi, int size)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct packet_command cgc;
struct modesel_head mh;

@@ -2790,7 +2788,7 @@ static int cdrom_switch_blocksize(struct cdrom_device_info *cdi, int size)
static int cdrom_get_track_info(struct cdrom_device_info *cdi,
__u16 track, __u8 type, track_information *ti)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct packet_command cgc;
int ret, buflen;

@@ -3049,7 +3047,7 @@ static noinline int mmc_ioctl_cdrom_play_msf(struct cdrom_device_info *cdi,
void __user *arg,
struct packet_command *cgc)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct cdrom_msf msf;
cd_dbg(CD_DO_IOCTL, "entering CDROMPLAYMSF\n");
if (copy_from_user(&msf, (struct cdrom_msf __user *)arg, sizeof(msf)))
@@ -3069,7 +3067,7 @@ static noinline int mmc_ioctl_cdrom_play_blk(struct cdrom_device_info *cdi,
void __user *arg,
struct packet_command *cgc)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
struct cdrom_blk blk;
cd_dbg(CD_DO_IOCTL, "entering CDROMPLAYBLK\n");
if (copy_from_user(&blk, (struct cdrom_blk __user *)arg, sizeof(blk)))
@@ -3164,7 +3162,7 @@ static noinline int mmc_ioctl_cdrom_start_stop(struct cdrom_device_info *cdi,
struct packet_command *cgc,
int cmd)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
cd_dbg(CD_DO_IOCTL, "entering CDROMSTART/CDROMSTOP\n");
cgc->cmd[0] = GPCMD_START_STOP_UNIT;
cgc->cmd[1] = 1;
@@ -3177,7 +3175,7 @@ static noinline int mmc_ioctl_cdrom_pause_resume(struct cdrom_device_info *cdi,
struct packet_command *cgc,
int cmd)
{
- struct cdrom_device_ops *cdo = cdi->ops;
+ const struct cdrom_device_ops *cdo = cdi->ops;
cd_dbg(CD_DO_IOCTL, "entering CDROMPAUSE/CDROMRESUME\n");
cgc->cmd[0] = GPCMD_PAUSE_RESUME;
cgc->cmd[8] = (cmd == CDROMRESUME) ? 1 : 0;
diff --git a/drivers/cdrom/gdrom.c b/drivers/cdrom/gdrom.c
index 584bc3126403..f1a6e520ac6e 100644
--- a/drivers/cdrom/gdrom.c
+++ b/drivers/cdrom/gdrom.c
@@ -481,7 +481,7 @@ static int gdrom_audio_ioctl(struct cdrom_device_info *cdi, unsigned int cmd,
return -EINVAL;
}

-static struct cdrom_device_ops gdrom_ops = {
+static const struct cdrom_device_ops gdrom_ops = {
.open = gdrom_open,
.release = gdrom_release,
.drive_status = gdrom_drivestatus,
@@ -489,9 +489,9 @@ static struct cdrom_device_ops gdrom_ops = {
.get_last_session = gdrom_get_last_session,
.reset = gdrom_hardreset,
.audio_ioctl = gdrom_audio_ioctl,
+ .generic_packet = cdrom_dummy_generic_packet,
.capability = CDC_MULTI_SESSION | CDC_MEDIA_CHANGED |
CDC_RESET | CDC_DRIVE_STATUS | CDC_CD_R,
- .n_minors = 1,
};

static int gdrom_bdops_open(struct block_device *bdev, fmode_t mode)
diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
index 9cbd217bc0c9..ab9232e1e16f 100644
--- a/drivers/ide/ide-cd.c
+++ b/drivers/ide/ide-cd.c
@@ -1166,7 +1166,7 @@ void ide_cdrom_update_speed(ide_drive_t *drive, u8 *buf)
CDC_CD_RW | CDC_DVD | CDC_DVD_R | CDC_DVD_RAM | CDC_GENERIC_PACKET | \
CDC_MO_DRIVE | CDC_MRW | CDC_MRW_W | CDC_RAM)

-static struct cdrom_device_ops ide_cdrom_dops = {
+static const struct cdrom_device_ops ide_cdrom_dops = {
.open = ide_cdrom_open_real,
.release = ide_cdrom_release_real,
.drive_status = ide_cdrom_drive_status,
diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 94352e4df831..013bfe049a48 100644
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -117,7 +117,7 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
unsigned int clearing, int slot);
static int sr_packet(struct cdrom_device_info *, struct packet_command *);

-static struct cdrom_device_ops sr_dops = {
+static const struct cdrom_device_ops sr_dops = {
.open = sr_open,
.release = sr_release,
.drive_status = sr_drive_status,
diff --git a/include/linux/cdrom.h b/include/linux/cdrom.h
index 8609d577bb66..6e8f209a6dff 100644
--- a/include/linux/cdrom.h
+++ b/include/linux/cdrom.h
@@ -36,7 +36,7 @@ struct packet_command

/* Uniform cdrom data structures for cdrom.c */
struct cdrom_device_info {
- struct cdrom_device_ops *ops; /* link to device_ops */
+ const struct cdrom_device_ops *ops; /* link to device_ops */
struct list_head list; /* linked list of all device_info */
struct gendisk *disk; /* matching block layer disk */
void *handle; /* driver-dependent data */
@@ -87,7 +87,6 @@ struct cdrom_device_ops {

/* driver specifications */
const int capability; /* capability flags */
- int n_minors; /* number of active minor devices */
/* handle uniform packets for scsi type devices (scsi,atapi) */
int (*generic_packet) (struct cdrom_device_info *,
struct packet_command *);
@@ -123,6 +122,8 @@ extern int cdrom_mode_sense(struct cdrom_device_info *cdi,
int page_code, int page_control);
extern void init_cdrom_command(struct packet_command *cgc,
void *buffer, int len, int type);
+extern int cdrom_dummy_generic_packet(struct cdrom_device_info *cdi,
+ struct packet_command *cgc);

/* The SCSI spec says there could be 256 slots. */
#define CDROM_MAX_SLOTS 256
--
2.7.4

--
Kees Cook
Pixel Security

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