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SubjectRe: [PATCH 0/2] (Was: perf_event_mmap(vma) && !vma->vm_mm)
On 10/16, Peter Zijlstra wrote:
>
> 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.

Thanks, can I have your acks for Ingo ?

> 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';

Yes, this is almost what I meant, but:

- name is "const char *", we need another variable

- we do not really need "len", we can simply do

size = strlen(name) + 1;
while (size % sizeof(u64))
name[size++] = '\0';

although I won't argue if you dislike "size & 7" in while().

- we can factor out strncpy(tmp, name).

Could you look at 3/2 I'll send in a minute?

Oleg.



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