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binder: Handle start==NULL in binder_update_page_range()

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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>
This commit is contained in:
Jann Horn 2019-10-18 22:56:31 +02:00 committed by Greg Kroah-Hartman
parent a7a74d7ff5
commit 2a9edd056e
1 changed files with 5 additions and 3 deletions
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8
drivers/android/binder_alloc.c
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@ -276,8 +276,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
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;
@ -290,6 +289,8 @@ free_range:
WARN_ON(!ret);
trace_binder_free_lru_end(alloc, index);
if (page_addr == start)
break;
continue;
err_vm_insert_page_failed:
@ -297,7 +298,8 @@ err_vm_insert_page_failed:
page->page_ptr = NULL;
err_alloc_page_failed:
err_page_ptr_cleared:
;
if (page_addr == start)
break;
}
err_no_vma:
if (mm) {