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authorTodd Kjos <tkjos@google.com>2021-12-20 22:01:50 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-12-21 13:07:34 +0300
commitcfd0d84ba28c18b531648c9d4a35ecca89ad9901 (patch)
treef454a0353d54eff36b10533f10c54765fe2fd1cf
parent2585cf9dfaaddf00b069673f27bb3f8530e2039c (diff)
downloadlinux-cfd0d84ba28c18b531648c9d4a35ecca89ad9901.tar.xz
binder: fix async_free_space accounting for empty parcels
In 4.13, commit 74310e06be4d ("android: binder: Move buffer out of area shared with user space") fixed a kernel structure visibility issue. As part of that patch, sizeof(void *) was used as the buffer size for 0-length data payloads so the driver could detect abusive clients sending 0-length asynchronous transactions to a server by enforcing limits on async_free_size. Unfortunately, on the "free" side, the accounting of async_free_space did not add the sizeof(void *) back. The result was that up to 8-bytes of async_free_space were leaked on every async transaction of 8-bytes or less. These small transactions are uncommon, so this accounting issue has gone undetected for several years. The fix is to use "buffer_size" (the allocated buffer size) instead of "size" (the logical buffer size) when updating the async_free_space during the free operation. These are the same except for this corner case of asynchronous transactions with payloads < 8 bytes. Fixes: 74310e06be4d ("android: binder: Move buffer out of area shared with user space") Signed-off-by: Todd Kjos <tkjos@google.com> Cc: stable@vger.kernel.org # 4.14+ Link: https://lore.kernel.org/r/20211220190150.2107077-1-tkjos@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/android/binder_alloc.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 340515f54498..47bc74a8c7b6 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -671,7 +671,7 @@ static void binder_free_buf_locked(struct binder_alloc *alloc,
BUG_ON(buffer->user_data > alloc->buffer + alloc->buffer_size);
if (buffer->async_transaction) {
- alloc->free_async_space += size + sizeof(struct binder_buffer);
+ alloc->free_async_space += buffer_size + sizeof(struct binder_buffer);
binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC_ASYNC,
"%d: binder_free_buf size %zd async free %zd\n",