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perf: Change zero-padding of strings in perf_event_mmap_event()

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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 <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-8jirlm99m6if2z13wd6rbyu6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2013-10-17 00:06:46 +02:00 committed by Ingo Molnar
parent 3ea2f2b96f
commit 2c42cfbfe1
1 changed files with 11 additions and 6 deletions
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17
kernel/events/core.c
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@ -5106,15 +5106,13 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
unsigned int size; unsigned int size;
char tmp[16]; char tmp[16];
char *buf = NULL; char *buf = NULL;
const char *name; char *name;
memset(tmp, 0, sizeof(tmp));
if (file) { if (file) {
struct inode *inode; struct inode *inode;
dev_t dev; dev_t dev;
buf = kzalloc(PATH_MAX, GFP_KERNEL); buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf) { if (!buf) {
name = strncpy(tmp, "//enomem", sizeof(tmp)); name = strncpy(tmp, "//enomem", sizeof(tmp));
goto got_name; goto got_name;
@ -5137,7 +5135,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
min = MINOR(dev); min = MINOR(dev);
} else { } else {
name = arch_vma_name(vma); name = (char *)arch_vma_name(vma);
if (name) { if (name) {
name = strncpy(tmp, name, sizeof(tmp) - 1); name = strncpy(tmp, name, sizeof(tmp) - 1);
tmp[sizeof(tmp) - 1] = '\0'; tmp[sizeof(tmp) - 1] = '\0';
@ -5160,7 +5158,14 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
} }
got_name: 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_name = name;
mmap_event->file_size = size; mmap_event->file_size = size;