[PATCH] add check to /proc/devices read routines

Patch to add check to get_chrdev_list and get_blkdev_list to prevent reads
of /proc/devices from spilling over the provided page if more than 4096
bytes of string data are generated from all the registered character and
block devices in a system

Signed-off-by: Neil Horman <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/block/genhd.c

···
 
 #ifdef CONFIG_PROC_FS
 /* get block device names in somewhat random order */
-int get_blkdev_list(char *p)
+int get_blkdev_list(char *p, int used)
 {
 	struct blk_major_name *n;
 	int i, len;
···
 
 	down(&block_subsys_sem);
 	for (i = 0; i < ARRAY_SIZE(major_names); i++) {
-		for (n = major_names[i]; n; n = n->next)
+		for (n = major_names[i]; n; n = n->next) {
+			/*
+			 * If the curent string plus the 5 extra characters
+			 * in the line would run us off the page, then we're done
+			 */
+			if ((len + used + strlen(n->name) + 5) >= PAGE_SIZE)
+				goto page_full;
 			len += sprintf(p+len, "%3d %s\n",
 				       n->major, n->name);
+		}
 	}
+page_full:
 	up(&block_subsys_sem);
 
 	return len;

fs/char_dev.c

···
 
 	down(&chrdevs_lock);
 	for (i = 0; i < ARRAY_SIZE(chrdevs) ; i++) {
-		for (cd = chrdevs[i]; cd; cd = cd->next)
+		for (cd = chrdevs[i]; cd; cd = cd->next) {
+			/*
+			 * if the current name, plus the 5 extra characters
+			 * in the device line for this entry
+			 * would run us off the page, we're done
+			 */
+			if ((len+strlen(cd->name) + 5) >= PAGE_SIZE)
+				goto page_full;
+
+
 			len += sprintf(page+len, "%3d %s\n",
 				       cd->major, cd->name);
+		}
 	}
+page_full:
 	up(&chrdevs_lock);
 
 	return len;

fs/proc/proc_misc.c

···
 				 int count, int *eof, void *data)
 {
 	int len = get_chrdev_list(page);
-	len += get_blkdev_list(page+len);
+	len += get_blkdev_list(page+len, len);
 	return proc_calc_metrics(page, start, off, count, eof, len);
 }
 

include/linux/genhd.h

···
 extern void disk_round_stats(struct gendisk *disk);
 
 /* drivers/block/genhd.c */
-extern int get_blkdev_list(char *);
+extern int get_blkdev_list(char *, int);
 extern void add_disk(struct gendisk *disk);
 extern void del_gendisk(struct gendisk *gp);
 extern void unlink_gendisk(struct gendisk *gp);