tee: shm: reject zero-sized allocations in tee_dyn_shm_alloc_helper()

tee_dyn_shm_alloc_helper() derives nr_pages from a caller-supplied size
and passes it to alloc_pages_exact() without checking it. For size == 0
nr_pages is 0, and alloc_pages_exact(0) calls get_order(0), which is
documented as undefined and returns BITS_PER_LONG - PAGE_SHIFT. The page
allocator then trips its order > MAX_PAGE_ORDER warning and fails the
allocation; on a panic_on_warn kernel that ends the boot.

This can be triggered by TEE_IOC_SHM_ALLOC with struct
tee_ioctl_shm_alloc_data where size is 0.

Reject a zero page count, as register_shm_helper() already does for the
register path.

Fixes: cf4441503e ("tee: optee: Move pool_op helper functions")
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Georgiy Osokin <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
Signed-off-by: Jens Wiklander <[email protected]>

drivers/tee/tee_shm.c

@@ -343,6 +343,10 @@ int tee_dyn_shm_alloc_helper(struct tee_shm *shm, size_t size, size_t align,
 	unsigned int i;
 	int rc = 0;
 
+	/* get_order(0) is undefined and exceeds MAX_PAGE_ORDER. */
+	if (!nr_pages)
+		return -EINVAL;
+
 	/*
 	 * Ignore alignment since this is already going to be page aligned
 	 * and there's no need for any larger alignment.