iommu/omap: Fix debug_read_tlb() to use seq_printf()

The debug_read_tlb() uses the sprintf() functions directly on the buffer
allocated by buf = kmalloc(count), without taking into account the size
of the buffer, with the consequence corrupting the heap, depending on
the count requested by the user.

The patch fixes the issue replacing sprintf() by seq_printf().
Signed-off-by: Salva Peiró <speirofr@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/omap-iommu-debug.c

@@ -133,26 +133,18 @@ __dump_tlb_entries(struct omap_iommu *obj, struct cr_regs *crs, int num)
 }
 
 static ssize_t iotlb_dump_cr(struct omap_iommu *obj, struct cr_regs *cr,
-			     char *buf)
+			     struct seq_file *s)
 {
-	char *p = buf;
-
-	/* FIXME: Need more detail analysis of cam/ram */
-	p += sprintf(p, "%08x %08x %01x\n", cr->cam, cr->ram,
-					(cr->cam & MMU_CAM_P) ? 1 : 0);
-
-	return p - buf;
+	return seq_printf(s, "%08x %08x %01x\n", cr->cam, cr->ram,
+			  (cr->cam & MMU_CAM_P) ? 1 : 0);
 }
 
-static size_t omap_dump_tlb_entries(struct omap_iommu *obj, char *buf,
-				    ssize_t bytes)
+static size_t omap_dump_tlb_entries(struct omap_iommu *obj, struct seq_file *s)
 {
 	int i, num;
 	struct cr_regs *cr;
-	char *p = buf;
 
-	num = bytes / sizeof(*cr);
-	num = min(obj->nr_tlb_entries, num);
+	num = obj->nr_tlb_entries;
 
 	cr = kcalloc(num, sizeof(*cr), GFP_KERNEL);
 	if (!cr)
@@ -160,40 +152,28 @@ static size_t omap_dump_tlb_entries(struct omap_iommu *obj, char *buf,
 
 	num = __dump_tlb_entries(obj, cr, num);
 	for (i = 0; i < num; i++)
-		p += iotlb_dump_cr(obj, cr + i, p);
+		iotlb_dump_cr(obj, cr + i, s);
 	kfree(cr);
 
-	return p - buf;
+	return 0;
 }
 
-static ssize_t debug_read_tlb(struct file *file, char __user *userbuf,
-			      size_t count, loff_t *ppos)
+static int debug_read_tlb(struct seq_file *s, void *data)
 {
-	struct omap_iommu *obj = file->private_data;
-	char *p, *buf;
-	ssize_t bytes, rest;
+	struct omap_iommu *obj = s->private;
 
 	if (is_omap_iommu_detached(obj))
 		return -EPERM;
 
-	buf = kmalloc(count, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-	p = buf;
-
 	mutex_lock(&iommu_debug_lock);
 
-	p += sprintf(p, "%8s %8s\n", "cam:", "ram:");
-	p += sprintf(p, "-----------------------------------------\n");
-	rest = count - (p - buf);
-	p += omap_dump_tlb_entries(obj, p, rest);
-
-	bytes = simple_read_from_buffer(userbuf, count, ppos, buf, p - buf);
+	seq_printf(s, "%8s %8s\n", "cam:", "ram:");
+	seq_puts(s, "-----------------------------------------\n");
+	omap_dump_tlb_entries(obj, s);
 
 	mutex_unlock(&iommu_debug_lock);
-	kfree(buf);
 
-	return bytes;
+	return 0;
 }
 
 static void dump_ioptable(struct seq_file *s)
@@ -268,7 +248,7 @@ static int debug_read_pagetable(struct seq_file *s, void *data)
 	}
 
 DEBUG_FOPS_RO(regs);
-DEBUG_FOPS_RO(tlb);
+DEBUG_SEQ_FOPS_RO(tlb);
 DEBUG_SEQ_FOPS_RO(pagetable);
 
 #define __DEBUG_ADD_FILE(attr, mode)					\