From: Jann Horn jannh@google.com
commit 2a9edd056ed4fbf9d2e797c3fc06335af35bccc4 upstream.
The old loop wouldn't stop when reaching `start` if `start==NULL`, instead continuing backwards to index -1 and crashing.
Luckily you need to be highly privileged to map things at NULL, so it's not a big problem.
Fix it by adjusting the loop so that the loop variable is always in bounds.
This patch is deliberately minimal to simplify backporting, but IMO this function could use a refactor. The jump labels in the second loop body are horrible (the error gotos should be jumping to free_range instead), and both loops would look nicer if they just iterated upwards through indices. And the up_read()+mmput() shouldn't be duplicated like that.
Cc: stable@vger.kernel.org Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Signed-off-by: Jann Horn jannh@google.com Acked-by: Christian Brauner christian.brauner@ubuntu.com Link: https://lore.kernel.org/r/20191018205631.248274-3-jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/android/binder_alloc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -289,8 +289,7 @@ static int binder_update_page_range(stru return 0;
free_range: - for (page_addr = end - PAGE_SIZE; page_addr >= start; - page_addr -= PAGE_SIZE) { + for (page_addr = end - PAGE_SIZE; 1; page_addr -= PAGE_SIZE) { bool ret; size_t index;
@@ -303,6 +302,8 @@ free_range: WARN_ON(!ret);
trace_binder_free_lru_end(alloc, index); + if (page_addr == start) + break; continue;
err_vm_insert_page_failed: @@ -312,7 +313,8 @@ err_map_kernel_failed: page->page_ptr = NULL; err_alloc_page_failed: err_page_ptr_cleared: - ; + if (page_addr == start) + break; } err_no_vma: if (mm) {