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compat_ioctl: don't look up the fd twice
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In code in fs/compat_ioctl.c that translates ioctl arguments
into a in-kernel structure, then performs sys_ioctl, possibly
under set_fs(KERNEL_DS), this commit changes the sys_ioctl
calls to do_ioctl calls. do_ioctl is a new function that does
the same thing as sys_ioctl, but doesn't look up the fd again.

This change is made to avoid (potential) security issues
because of ioctl handlers that accept one of the ioctl
commands I2C_FUNCS, VIDEO_GET_EVENT, MTIOCPOS, MTIOCGET,
TIOCGSERIAL, TIOCSSERIAL, RTC_IRQP_READ, RTC_EPOCH_READ.
This can happen for multiple reasons:

 - The ioctl command number could be reused.
 - The ioctl handler might not check the full ioctl
   command. This is e.g. true for drm_ioctl.
 - The ioctl handler is very special, e.g. cuse_file_ioctl

The real issue is that set_fs(KERNEL_DS) is used here,
but that's fixed in a separate commit
"compat_ioctl: don't call do_ioctl under set_fs(KERNEL_DS)".

This change mitigates potential security issues by
preventing a race that permits invocation of
unlocked_ioctl handlers under KERNEL_DS through compat
code even if a corresponding compat_ioctl handler exists.

So far, no way has been identified to use this to damage
kernel memory without having CAP_SYS_ADMIN in the init ns
(with the capability, doing reads/writes at arbitrary
kernel addresses should be easy through CUSE's ioctl
handler with FUSE_IOCTL_UNRESTRICTED set).

[AV: two missed sys_ioctl() taken care of]

Signed-off-by: Jann Horn <jann@thejh.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Jann Horn authored and Al Viro committed Jan 9, 2016
1 parent 1683098 commit b434172
Showing 1 changed file with 68 additions and 54 deletions.
122 changes: 68 additions & 54 deletions fs/compat_ioctl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -115,15 +115,27 @@
#include <asm/fbio.h>
#endif

static int w_long(unsigned int fd, unsigned int cmd,
compat_ulong_t __user *argp)
static int do_ioctl(struct file *file, unsigned int fd,
unsigned int cmd, unsigned long arg)
{
int err;

err = security_file_ioctl(file, cmd, arg);
if (err)
return err;

return do_vfs_ioctl(file, fd, cmd, arg);
}

static int w_long(struct file *file, unsigned int fd,
unsigned int cmd, compat_ulong_t __user *argp)
{
mm_segment_t old_fs = get_fs();
int err;
unsigned long val;

set_fs (KERNEL_DS);
err = sys_ioctl(fd, cmd, (unsigned long)&val);
err = do_ioctl(file, fd, cmd, (unsigned long)&val);
set_fs (old_fs);
if (!err && put_user(val, argp))
return -EFAULT;
Expand All @@ -139,15 +151,15 @@ struct compat_video_event {
} u;
};

static int do_video_get_event(unsigned int fd, unsigned int cmd,
struct compat_video_event __user *up)
static int do_video_get_event(struct file *file, unsigned int fd,
unsigned int cmd, struct compat_video_event __user *up)
{
struct video_event kevent;
mm_segment_t old_fs = get_fs();
int err;

set_fs(KERNEL_DS);
err = sys_ioctl(fd, cmd, (unsigned long) &kevent);
err = do_ioctl(file, fd, cmd, (unsigned long) &kevent);
set_fs(old_fs);

if (!err) {
Expand All @@ -169,8 +181,8 @@ struct compat_video_still_picture {
int32_t size;
};

static int do_video_stillpicture(unsigned int fd, unsigned int cmd,
struct compat_video_still_picture __user *up)
static int do_video_stillpicture(struct file *file, unsigned int fd,
unsigned int cmd, struct compat_video_still_picture __user *up)
{
struct video_still_picture __user *up_native;
compat_uptr_t fp;
Expand All @@ -190,7 +202,7 @@ static int do_video_stillpicture(unsigned int fd, unsigned int cmd,
if (err)
return -EFAULT;

err = sys_ioctl(fd, cmd, (unsigned long) up_native);
err = do_ioctl(file, fd, cmd, (unsigned long) up_native);

return err;
}
Expand All @@ -200,8 +212,8 @@ struct compat_video_spu_palette {
compat_uptr_t palette;
};

static int do_video_set_spu_palette(unsigned int fd, unsigned int cmd,
struct compat_video_spu_palette __user *up)
static int do_video_set_spu_palette(struct file *file, unsigned int fd,
unsigned int cmd, struct compat_video_spu_palette __user *up)
{
struct video_spu_palette __user *up_native;
compat_uptr_t palp;
Expand All @@ -218,7 +230,7 @@ static int do_video_set_spu_palette(unsigned int fd, unsigned int cmd,
if (err)
return -EFAULT;

err = sys_ioctl(fd, cmd, (unsigned long) up_native);
err = do_ioctl(file, fd, cmd, (unsigned long) up_native);

return err;
}
Expand Down Expand Up @@ -276,7 +288,7 @@ static int sg_build_iovec(sg_io_hdr_t __user *sgio, void __user *dxferp, u16 iov
return 0;
}

static int sg_ioctl_trans(unsigned int fd, unsigned int cmd,
static int sg_ioctl_trans(struct file *file, unsigned int fd, unsigned int cmd,
sg_io_hdr32_t __user *sgio32)
{
sg_io_hdr_t __user *sgio;
Expand All @@ -289,7 +301,7 @@ static int sg_ioctl_trans(unsigned int fd, unsigned int cmd,
if (get_user(interface_id, &sgio32->interface_id))
return -EFAULT;
if (interface_id != 'S')
return sys_ioctl(fd, cmd, (unsigned long)sgio32);
return do_ioctl(file, fd, cmd, (unsigned long)sgio32);

if (get_user(iovec_count, &sgio32->iovec_count))
return -EFAULT;
Expand Down Expand Up @@ -349,7 +361,7 @@ static int sg_ioctl_trans(unsigned int fd, unsigned int cmd,
if (put_user(compat_ptr(data), &sgio->usr_ptr))
return -EFAULT;

err = sys_ioctl(fd, cmd, (unsigned long) sgio);
err = do_ioctl(file, fd, cmd, (unsigned long) sgio);

if (err >= 0) {
void __user *datap;
Expand Down Expand Up @@ -380,13 +392,13 @@ struct compat_sg_req_info { /* used by SG_GET_REQUEST_TABLE ioctl() */
int unused;
};

static int sg_grt_trans(unsigned int fd, unsigned int cmd, struct
compat_sg_req_info __user *o)
static int sg_grt_trans(struct file *file, unsigned int fd,
unsigned int cmd, struct compat_sg_req_info __user *o)
{
int err, i;
sg_req_info_t __user *r;
r = compat_alloc_user_space(sizeof(sg_req_info_t)*SG_MAX_QUEUE);
err = sys_ioctl(fd,cmd,(unsigned long)r);
err = do_ioctl(file, fd, cmd, (unsigned long)r);
if (err < 0)
return err;
for (i = 0; i < SG_MAX_QUEUE; i++) {
Expand All @@ -412,8 +424,8 @@ struct sock_fprog32 {
#define PPPIOCSPASS32 _IOW('t', 71, struct sock_fprog32)
#define PPPIOCSACTIVE32 _IOW('t', 70, struct sock_fprog32)

static int ppp_sock_fprog_ioctl_trans(unsigned int fd, unsigned int cmd,
struct sock_fprog32 __user *u_fprog32)
static int ppp_sock_fprog_ioctl_trans(struct file *file, unsigned int fd,
unsigned int cmd, struct sock_fprog32 __user *u_fprog32)
{
struct sock_fprog __user *u_fprog64 = compat_alloc_user_space(sizeof(struct sock_fprog));
void __user *fptr64;
Expand All @@ -435,7 +447,7 @@ static int ppp_sock_fprog_ioctl_trans(unsigned int fd, unsigned int cmd,
else
cmd = PPPIOCSACTIVE;

return sys_ioctl(fd, cmd, (unsigned long) u_fprog64);
return do_ioctl(file, fd, cmd, (unsigned long) u_fprog64);
}

struct ppp_option_data32 {
Expand All @@ -451,7 +463,7 @@ struct ppp_idle32 {
};
#define PPPIOCGIDLE32 _IOR('t', 63, struct ppp_idle32)

static int ppp_gidle(unsigned int fd, unsigned int cmd,
static int ppp_gidle(struct file *file, unsigned int fd, unsigned int cmd,
struct ppp_idle32 __user *idle32)
{
struct ppp_idle __user *idle;
Expand All @@ -460,7 +472,7 @@ static int ppp_gidle(unsigned int fd, unsigned int cmd,

idle = compat_alloc_user_space(sizeof(*idle));

err = sys_ioctl(fd, PPPIOCGIDLE, (unsigned long) idle);
err = do_ioctl(file, fd, PPPIOCGIDLE, (unsigned long) idle);

if (!err) {
if (get_user(xmit, &idle->xmit_idle) ||
Expand All @@ -472,7 +484,7 @@ static int ppp_gidle(unsigned int fd, unsigned int cmd,
return err;
}

static int ppp_scompress(unsigned int fd, unsigned int cmd,
static int ppp_scompress(struct file *file, unsigned int fd, unsigned int cmd,
struct ppp_option_data32 __user *odata32)
{
struct ppp_option_data __user *odata;
Expand All @@ -492,7 +504,7 @@ static int ppp_scompress(unsigned int fd, unsigned int cmd,
sizeof(__u32) + sizeof(int)))
return -EFAULT;

return sys_ioctl(fd, PPPIOCSCOMPRESS, (unsigned long) odata);
return do_ioctl(file, fd, PPPIOCSCOMPRESS, (unsigned long) odata);
}

#ifdef CONFIG_BLOCK
Expand All @@ -512,7 +524,8 @@ struct mtpos32 {
};
#define MTIOCPOS32 _IOR('m', 3, struct mtpos32)

static int mt_ioctl_trans(unsigned int fd, unsigned int cmd, void __user *argp)
static int mt_ioctl_trans(struct file *file, unsigned int fd,
unsigned int cmd, void __user *argp)
{
mm_segment_t old_fs = get_fs();
struct mtget get;
Expand All @@ -534,7 +547,7 @@ static int mt_ioctl_trans(unsigned int fd, unsigned int cmd, void __user *argp)
break;
}
set_fs (KERNEL_DS);
err = sys_ioctl (fd, kcmd, (unsigned long)karg);
err = do_ioctl(file, fd, kcmd, (unsigned long)karg);
set_fs (old_fs);
if (err)
return err;
Expand Down Expand Up @@ -605,8 +618,8 @@ struct serial_struct32 {
compat_int_t reserved[1];
};

static int serial_struct_ioctl(unsigned fd, unsigned cmd,
struct serial_struct32 __user *ss32)
static int serial_struct_ioctl(struct file *file, unsigned fd,
unsigned cmd, struct serial_struct32 __user *ss32)
{
typedef struct serial_struct32 SS32;
int err;
Expand All @@ -629,7 +642,7 @@ static int serial_struct_ioctl(unsigned fd, unsigned cmd,
ss.iomap_base = 0UL;
}
set_fs(KERNEL_DS);
err = sys_ioctl(fd,cmd,(unsigned long)(&ss));
err = do_ioctl(file, fd, cmd, (unsigned long)&ss);
set_fs(oldseg);
if (cmd == TIOCGSERIAL && err >= 0) {
if (!access_ok(VERIFY_WRITE, ss32, sizeof(SS32)))
Expand Down Expand Up @@ -674,8 +687,8 @@ struct i2c_rdwr_aligned {
struct i2c_msg msgs[0];
};

static int do_i2c_rdwr_ioctl(unsigned int fd, unsigned int cmd,
struct i2c_rdwr_ioctl_data32 __user *udata)
static int do_i2c_rdwr_ioctl(struct file *file, unsigned int fd,
unsigned int cmd, struct i2c_rdwr_ioctl_data32 __user *udata)
{
struct i2c_rdwr_aligned __user *tdata;
struct i2c_msg __user *tmsgs;
Expand Down Expand Up @@ -708,11 +721,11 @@ static int do_i2c_rdwr_ioctl(unsigned int fd, unsigned int cmd,
put_user(compat_ptr(datap), &tmsgs[i].buf))
return -EFAULT;
}
return sys_ioctl(fd, cmd, (unsigned long)tdata);
return do_ioctl(file, fd, cmd, (unsigned long)tdata);
}

static int do_i2c_smbus_ioctl(unsigned int fd, unsigned int cmd,
struct i2c_smbus_ioctl_data32 __user *udata)
static int do_i2c_smbus_ioctl(struct file *file, unsigned int fd,
unsigned int cmd, struct i2c_smbus_ioctl_data32 __user *udata)
{
struct i2c_smbus_ioctl_data __user *tdata;
compat_caddr_t datap;
Expand All @@ -734,15 +747,16 @@ static int do_i2c_smbus_ioctl(unsigned int fd, unsigned int cmd,
__put_user(compat_ptr(datap), &tdata->data))
return -EFAULT;

return sys_ioctl(fd, cmd, (unsigned long)tdata);
return do_ioctl(file, fd, cmd, (unsigned long)tdata);
}

#define RTC_IRQP_READ32 _IOR('p', 0x0b, compat_ulong_t)
#define RTC_IRQP_SET32 _IOW('p', 0x0c, compat_ulong_t)
#define RTC_EPOCH_READ32 _IOR('p', 0x0d, compat_ulong_t)
#define RTC_EPOCH_SET32 _IOW('p', 0x0e, compat_ulong_t)

static int rtc_ioctl(unsigned fd, unsigned cmd, void __user *argp)
static int rtc_ioctl(struct file *file, unsigned fd,
unsigned cmd, void __user *argp)
{
mm_segment_t oldfs = get_fs();
compat_ulong_t val32;
Expand All @@ -753,7 +767,7 @@ static int rtc_ioctl(unsigned fd, unsigned cmd, void __user *argp)
case RTC_IRQP_READ32:
case RTC_EPOCH_READ32:
set_fs(KERNEL_DS);
ret = sys_ioctl(fd, (cmd == RTC_IRQP_READ32) ?
ret = do_ioctl(file, fd, (cmd == RTC_IRQP_READ32) ?
RTC_IRQP_READ : RTC_EPOCH_READ,
(unsigned long)&kval);
set_fs(oldfs);
Expand All @@ -762,9 +776,9 @@ static int rtc_ioctl(unsigned fd, unsigned cmd, void __user *argp)
val32 = kval;
return put_user(val32, (unsigned int __user *)argp);
case RTC_IRQP_SET32:
return sys_ioctl(fd, RTC_IRQP_SET, (unsigned long)argp);
return do_ioctl(file, fd, RTC_IRQP_SET, (unsigned long)argp);
case RTC_EPOCH_SET32:
return sys_ioctl(fd, RTC_EPOCH_SET, (unsigned long)argp);
return do_ioctl(file, fd, RTC_EPOCH_SET, (unsigned long)argp);
}

return -ENOIOCTLCMD;
Expand Down Expand Up @@ -1443,46 +1457,46 @@ static long do_ioctl_trans(int fd, unsigned int cmd,

switch (cmd) {
case PPPIOCGIDLE32:
return ppp_gidle(fd, cmd, argp);
return ppp_gidle(file, fd, cmd, argp);
case PPPIOCSCOMPRESS32:
return ppp_scompress(fd, cmd, argp);
return ppp_scompress(file, fd, cmd, argp);
case PPPIOCSPASS32:
case PPPIOCSACTIVE32:
return ppp_sock_fprog_ioctl_trans(fd, cmd, argp);
return ppp_sock_fprog_ioctl_trans(file, fd, cmd, argp);
#ifdef CONFIG_BLOCK
case SG_IO:
return sg_ioctl_trans(fd, cmd, argp);
return sg_ioctl_trans(file, fd, cmd, argp);
case SG_GET_REQUEST_TABLE:
return sg_grt_trans(fd, cmd, argp);
return sg_grt_trans(file, fd, cmd, argp);
case MTIOCGET32:
case MTIOCPOS32:
return mt_ioctl_trans(fd, cmd, argp);
return mt_ioctl_trans(file, fd, cmd, argp);
#endif
/* Serial */
case TIOCGSERIAL:
case TIOCSSERIAL:
return serial_struct_ioctl(fd, cmd, argp);
return serial_struct_ioctl(file, fd, cmd, argp);
/* i2c */
case I2C_FUNCS:
return w_long(fd, cmd, argp);
return w_long(file, fd, cmd, argp);
case I2C_RDWR:
return do_i2c_rdwr_ioctl(fd, cmd, argp);
return do_i2c_rdwr_ioctl(file, fd, cmd, argp);
case I2C_SMBUS:
return do_i2c_smbus_ioctl(fd, cmd, argp);
return do_i2c_smbus_ioctl(file, fd, cmd, argp);
/* Not implemented in the native kernel */
case RTC_IRQP_READ32:
case RTC_IRQP_SET32:
case RTC_EPOCH_READ32:
case RTC_EPOCH_SET32:
return rtc_ioctl(fd, cmd, argp);
return rtc_ioctl(file, fd, cmd, argp);

/* dvb */
case VIDEO_GET_EVENT:
return do_video_get_event(fd, cmd, argp);
return do_video_get_event(file, fd, cmd, argp);
case VIDEO_STILLPICTURE:
return do_video_stillpicture(fd, cmd, argp);
return do_video_stillpicture(file, fd, cmd, argp);
case VIDEO_SET_SPU_PALETTE:
return do_video_set_spu_palette(fd, cmd, argp);
return do_video_set_spu_palette(file, fd, cmd, argp);
}

/*
Expand Down

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