[PATCH v2] ntsync: Check wait count based on byte size.

[Elizabeth Figura]

GCC versions below 13 incorrectly detect the copy size as being static and too
small to fit in the "fds" array. Work around this by explicitly calculating the
size and returning EINVAL based on that, instead of based on the object count.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Suggested-by: Arnd Bergmann 
Signed-off-by: Elizabeth Figura

--

Suggested-by as per Arnd's request, but the only thing I changed was preserving
array_size() [as noted by Geert in the linked thread]. I tested and found no
regressions.

v2: Add missing sign-off

---
 drivers/misc/ntsync.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c
index 586b86243e1d..24cb2f71186a 100644
--- a/drivers/misc/ntsync.c
+++ b/drivers/misc/ntsync.c
@@ -873,6 +873,7 @@ static int setup_wait(struct ntsync_device *dev,
 {
    int fds[NTSYNC_MAX_WAIT_COUNT + 1];
    const __u32 count = args->count;
+	size_t size = array_size(count, sizeof(fds[0]));
    struct ntsync_q *q;
    __u32 total_count;
    __u32 i, j;
@@ -880,15 +881,14 @@ static int setup_wait(struct ntsync_device *dev,
    if (args->pad || (args->flags & ~NTSYNC_WAIT_REALTIME))
    	return -EINVAL;

-	if (args->count > NTSYNC_MAX_WAIT_COUNT)
+	if (size >= sizeof(fds))
    	return -EINVAL;

total_count = count;
    if (args->alert)
    	total_count++;

-	if (copy_from_user(fds, u64_to_user_ptr(args->objs),
-			   array_size(count, sizeof(*fds))))
+	if (copy_from_user(fds, u64_to_user_ptr(args->objs), size))
    	return -EFAULT;
    if (args->alert)
    	fds[count] = args->alert;

[Elizabeth Figura]

On Thursday, 20 February 2025 13:23:34 CST Elizabeth Figura wrote:
> GCC versions below 13 incorrectly detect the copy size as being static and too
> small to fit in the "fds" array. Work around this by explicitly calculating the
> size and returning EINVAL based on that, instead of based on the object count.
>
> Reported-by: kernel test robot 
> Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
> Suggested-by: Arnd Bergmann 
> Signed-off-by: Elizabeth Figura

Oops, I forgot to include a reference to v1:

https://lore.kernel.org/all/[e-mail]/