Re: [PATCH 0/2] (Was: perf_event_mmap(vma) && !vma->vm_mm)

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 16, 2013 at 10:58:00PM +0200, Oleg Nesterov wrote:
> OK. I'll wait for your review on this series, then send the next patch.
> 

Those two patches look good; thanks. How about something like so on top?

---
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5103,18 +5103,16 @@ static void perf_event_mmap_event(struct
 	struct file *file = vma->vm_file;
 	int maj = 0, min = 0;
 	u64 ino = 0, gen = 0;
-	unsigned int size;
+	unsigned int size, len;
 	char tmp[16];
 	char *buf = NULL;
 	const char *name;
 
-	memset(tmp, 0, sizeof(tmp));
-
 	if (file) {
 		struct inode *inode;
 		dev_t dev;
 
-		buf = kzalloc(PATH_MAX, GFP_KERNEL);
+		buf = kmalloc(PATH_MAX, GFP_KERNEL);
 		if (!buf) {
 			name = strncpy(tmp, "//enomem", sizeof(tmp));
 			goto got_name;
@@ -5160,7 +5158,15 @@ static void perf_event_mmap_event(struct
 	}
 
 got_name:
-	size = ALIGN(strlen(name)+1, sizeof(u64));
+	/*
+	 * Since our buffer works in 8 byte units we need to align our string
+	 * size to a multiple of 8. However, we must guarantee the tail end is
+	 * zero'd out to avoid leaking random bits to userspace.
+	 */
+	len = strlen(name)+1;
+	size = ALIGN(len, sizeof(u64));
+	for (; len < size; len++)
+		name[len] = '\0';
 
 	mmap_event->file_name = name;
 	mmap_event->file_size = size;