[PATCH] provide temporary device node for callouts to access the device

%N will create a temporary node for a callout a be sustituted with the
name of the node.

namedev.c

@@ -201,6 +201,12 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 
 
 		switch (c) {
+		case 'p':
+			if (strlen(udev->devpath) == 0)
+				break;
+			strfieldcatmax(string, udev->devpath, maxsize);
+			dbg("substitute kernel name '%s'", udev->kernel_name);
+			break;
 		case 'b':
 			if (strlen(udev->bus_id) == 0)
 				break;
@@ -290,6 +296,15 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 				strfieldcatmax(string, temp2, maxsize);
 			}
 			break;
+		case 'N':
+			if (udev->tmp_node[0] == '\0') {
+				dbg("create temporary device node for callout");
+				snprintf(udev->tmp_node, NAME_SIZE-1, "%s/.tmp-%u-%u", udev_root, udev->major, udev->minor);
+				udev_make_node(udev, udev->tmp_node, udev->major, udev->minor, 0600, 0, 0);
+			}
+			strfieldcatmax(string, udev->tmp_node, maxsize);
+			dbg("substitute temporary device node name '%s'", udev->tmp_node);
+			break;
 		default:
 			dbg("unknown substitution type '%%%c'", c);
 			break;
@@ -787,5 +802,11 @@ int namedev_name_device(struct udevice *udev, struct sysfs_class_device *class_d
 	dbg("no rule found, use kernel name '%s'", udev->name);
 
 exit:
+	if (udev->tmp_node[0] != '\0') {
+		dbg("removing temporary device node");
+		unlink_secure(udev->tmp_node);
+		udev->tmp_node[0] = '\0';
+	}
+
 	return 0;
 }

test/udev-test.pl

@@ -1066,6 +1066,24 @@ EOF
 		conf		=> <<EOF
 BUS="scsi", KERNEL="sda", NAME="should_not_match", DRIVER="sd-wrong"
 BUS="scsi", KERNEL="sda", NAME="node", DRIVER="sd"
+EOF
+	},
+	{
+		desc		=> "temporary node creation test",
+		subsys		=> "block",
+		devpath		=> "/block/sda",
+		exp_name	=> "sda",
+		conf		=> <<EOF
+BUS="scsi", KERNEL="sda", PROGRAM="/usr/bin/test -b %N" NAME="%N"
+EOF
+	},
+	{
+		desc		=> "devpath substitution test",
+		subsys		=> "block",
+		devpath		=> "/block/sda",
+		exp_name	=> "sda",
+		conf		=> <<EOF
+BUS="scsi", KERNEL="sda", PROGRAM="/bin/echo %p", RESULT="/block/sda" NAME="%k"
 EOF
 	},
 );

udev.8.in

@@ -188,6 +188,9 @@ For example, 'sda3' has a "kernel number" of '3'.
 .B %k
 The "kernel name" for the device.
 .TP
+.B %p
+The devpath for the device.
+.TP
 .B %M
 The kernel major number for the device.
 .TP
@@ -211,6 +214,10 @@ If the number is followed by the + char this part plus
 all remaining parts of the result string are substituted:
 .BI %c{ N+ }
 .TP
+.B %N
+The name of a created temporary device node to provide access to the
+device from a external program.
+.TP
 .BI %s{ filename }
 The content of a sysfs attribute.
 .TP

udev.h

@@ -23,6 +23,7 @@
 #ifndef _UDEV_H_
 #define _UDEV_H_
 
+#include <sys/types.h>
 #include <sys/param.h>
 #include "libsysfs/sysfs/libsysfs.h"
 
@@ -59,6 +60,7 @@ struct udevice {
 	int minor;
 
 	char devname[NAME_SIZE];
+	char tmp_node[NAME_SIZE];
 	int partitions;
 	int ignore_remove;
 	int config_line;
@@ -75,6 +77,7 @@ extern int udev_remove_device(struct udevice *udev);
 extern void udev_init_config(void);
 extern int udev_start(void);
 extern void udev_multiplex_directory(struct udevice *udev, const char *basedir, const char *suffix);
+extern int udev_make_node(struct udevice *udev, const char *file, int major, int minor, mode_t mode, uid_t uid, gid_t gid);
 
 extern char sysfs_path[SYSFS_PATH_MAX];
 extern char udev_root[PATH_MAX];

udev_add.c

@@ -67,7 +67,7 @@ error:
 	return -1;
 }
 
-static int make_node(struct udevice *udev, char *file, int major, int minor, unsigned int mode, uid_t uid, gid_t gid)
+int udev_make_node(struct udevice *udev, const char *file, int major, int minor, mode_t mode, uid_t uid, gid_t gid)
 {
 	struct stat stats;
 	int retval = 0;
@@ -183,7 +183,7 @@ static int create_node(struct udevice *udev)
 
 	if (!udev->test_run) {
 		info("creating device node '%s'", filename);
-		if (make_node(udev, filename, udev->major, udev->minor, udev->mode, uid, gid) != 0)
+		if (udev_make_node(udev, filename, udev->major, udev->minor, udev->mode, uid, gid) != 0)
 			goto error;
 	} else {
 		info("creating device node '%s', major = '%d', minor = '%d', "
@@ -198,7 +198,7 @@ static int create_node(struct udevice *udev)
 			for (i = 1; i <= udev->partitions; i++) {
 				strfieldcpy(partitionname, filename);
 				strintcat(partitionname, i);
-				make_node(udev, partitionname, udev->major, udev->minor + i, udev->mode, uid, gid);
+				udev_make_node(udev, partitionname, udev->major, udev->minor + i, udev->mode, uid, gid);
 			}
 		}
 	}

udev_remove.c

@@ -67,41 +67,6 @@ static int delete_path(const char *path)
 	return 0;
 }
 
-/** Remove all permissions on the device node, before
-  * unlinking it. This fixes a security issue.
-  * If the user created a hard-link to the device node,
-  * he can't use it any longer, because he lost permission
-  * to do so.
-  */
-static int secure_unlink(const char *filename)
-{
-	int retval;
-
-	retval = chown(filename, 0, 0);
-	if (retval) {
-		dbg("chown(%s, 0, 0) failed with error '%s'",
-		    filename, strerror(errno));
-		/* We continue nevertheless.
-		 * I think it's very unlikely for chown
-		 * to fail here, if the file exists.
-		 */
-	}
-	retval = chmod(filename, 0000);
-	if (retval) {
-		dbg("chmod(%s, 0000) failed with error '%s'",
-		    filename, strerror(errno));
-		/* We continue nevertheless. */
-	}
-	retval = unlink(filename);
-	if (errno == ENOENT)
-		retval = 0;
-	if (retval) {
-		dbg("unlink(%s) failed with error '%s'",
-			filename, strerror(errno));
-	}
-	return retval;
-}
-
 static int delete_node(struct udevice *udev)
 {
 	char filename[NAME_SIZE];
@@ -116,7 +81,7 @@ static int delete_node(struct udevice *udev)
 	filename[NAME_SIZE-1] = '\0';
 
 	info("removing device node '%s'", filename);
-	retval = secure_unlink(filename);
+	retval = unlink_secure(filename);
 	if (retval)
 		return retval;
 
@@ -131,7 +96,7 @@ static int delete_node(struct udevice *udev)
 		for (i = 1; i <= num; i++) {
 			strfieldcpy(partitionname, filename);
 			strintcat(partitionname, i);
-			secure_unlink(partitionname);
+			unlink_secure(partitionname);
 		}
 	}
 

udev_utils.c

@@ -112,6 +112,31 @@ int create_path(const char *path)
 	return mkdir(p, 0755);
 }
 
+/* Reset permissions on the device node, before unlinking it to make sure,
+ * that permisions of possible hard links will be removed to.
+ */
+int unlink_secure(const char *filename)
+{
+	int retval;
+
+	retval = chown(filename, 0, 0);
+	if (retval)
+		dbg("chown(%s, 0, 0) failed with error '%s'", filename, strerror(errno));
+
+	retval = chmod(filename, 0000);
+	if (retval)
+		dbg("chmod(%s, 0000) failed with error '%s'", filename, strerror(errno));
+
+	retval = unlink(filename);
+	if (errno == ENOENT)
+		retval = 0;
+
+	if (retval)
+		dbg("unlink(%s) failed with error '%s'", filename, strerror(errno));
+
+	return retval;
+}
+
 int parse_get_pair(char **orig_string, char **left, char **right)
 {
 	char *temp;

udev_utils.h

@@ -80,6 +80,7 @@ extern void udev_init_device(struct udevice *udev, const char* devpath, const ch
 extern int kernel_release_satisfactory(unsigned int version, unsigned int patchlevel, unsigned int sublevel);
 extern int create_path(const char *path);
 extern int parse_get_pair(char **orig_string, char **left, char **right);
+extern int unlink_secure(const char *filename);
 extern int file_map(const char *filename, char **buf, size_t *bufsize);
 extern void file_unmap(char *buf, size_t bufsize);
 extern size_t buf_get_line(const char *buf, size_t buflen, size_t cur);