compat_ioctl: don't look up the fd twice

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>

fs/compat_ioctl.c

@@ -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;
@@ -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) {
@@ -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;
@@ -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;
 }
@@ -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;
@@ -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;
 }
@@ -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;
@@ -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;
@@ -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;
@@ -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++) {
@@ -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;
@@ -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 {
@@ -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;
@@ -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) ||
@@ -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;
@@ -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
@@ -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;
@@ -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;
@@ -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;
@@ -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)))
@@ -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;
@@ -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;
@@ -734,7 +747,7 @@ 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)
@@ -742,7 +755,8 @@ static int do_i2c_smbus_ioctl(unsigned int fd, unsigned int cmd,
 #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;
@@ -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);
@@ -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;
@@ -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);
 	}
 
 	/*