On Thu, Oct 17, 2013 at 05:27:17PM +0200, Oleg Nesterov wrote: > On 10/17, Oleg Nesterov wrote: > > > > - 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(). > > Or, perhaps, > > while (!IS_ALIGNED(size, sizeof(u64))) > name[size++] = '\0'; >
--- Subject: perf: Change zero-padding of strings in perf_event_mmap_event() From: Peter Zijlstra <pet...@infradead.org> Date: Thu Oct 17 00:06:46 CEST 2013 Oleg complained about the excessive 0-ing in perf_event_mmap_event(), so try and be smarter about it while keeping it fairly fool proof and avoid leaking random bits out to userspace. Suggested-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/n/tip-8jirlm99m6if2z13wd6rb...@git.kernel.org --- kernel/events/core.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5106,15 +5106,13 @@ static void perf_event_mmap_event(struct unsigned int size; char tmp[16]; char *buf = NULL; - const char *name; - - memset(tmp, 0, sizeof(tmp)); + char *name; 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; @@ -5137,7 +5135,7 @@ static void perf_event_mmap_event(struct min = MINOR(dev); } else { - name = arch_vma_name(vma); + name = (char *)arch_vma_name(vma); if (name) { name = strncpy(tmp, name, sizeof(tmp) - 1); tmp[sizeof(tmp) - 1] = '\0'; @@ -5160,7 +5158,14 @@ 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. + */ + size = strlen(name)+1; + while (!IS_ALIGNED(size, sizeof(u64))) + name[size++] = '\0'; mmap_event->file_name = name; mmap_event->file_size = size; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
