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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2df37b8c8basm6762195ad.61.2026.09.19.14.36.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 14:36:49 -0700 (PDT) From: Hui Peng To: gregkh@linuxfoundation.org, arve@android.com, tkjos@android.com, brauner@kernel.org, cmllamas@google.com, aliceryhl@google.com Cc: linux-kernel@vger.kernel.org Subject: [PATCH] binder: fix sender fd 0 close and file refcount leak on TF_UPDATE_TXN Date: Sat, 19 Sep 2026 21:36:48 +0000 Message-ID: <20260919213648.3316566-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In `binder_proc_transaction()`, when a oneway transaction with `TF_UPDATE_TXN` supersedes an outdated pending transaction (`t_outdated`), the driver calls `binder_release_entire_buffer(proc, NULL, buffer, false)` and `kfree(t_outdated)`. Passing `is_failure = false` while `buffer->transaction` has already been set to `NULL` causes two bugs when `t_outdated` contained `BINDER_TYPE_FDA` or `BINDER_TYPE_FD` objects: 1. For `BINDER_TYPE_FDA`, `binder_translate_fd_array()` never wrote recipient file descriptors into the buffer (it only appended `struct file *` entries to `t_outdated->fd_fixups`), so the FD array in `buffer` still contains zeros (or sender-supplied offsets). Because `is_failure` is `false`, `binder_transaction_buffer_release()` executes the `!is_failure` branch on `BINDER_TYPE_FDA` and calls `binder_deferred_fd_close(fd)` (closing `fd 0` in `current->files`, which is the **sender** process!). 2. `t_outdated` is freed via `kfree(t_outdated)` without calling `binder_free_txn_fixups(t_outdated)`, permanently leaking every translated `struct file` reference in `t_outdated->fd_fixups`. Pass `is_failure = true` to `binder_release_entire_buffer()` and call `binder_free_txn_fixups(t_outdated)` before freeing `t_outdated`. Fixes: 9864bb480133 ("Binder: add TF_UPDATE_TXN to replace outdated txn") Fixes: bdc1c5fac982 ("binder: fix UAF caused by faulty buffer cleanup") Assisted-by: LLM Signed-off-by: Hui Peng --- drivers/android/binder.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8f2ef1bd539f..bc8bc9ee43a5 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2930,8 +2930,9 @@ static int binder_proc_transaction(struct binder_transaction *t, t_outdated->buffer = NULL; buffer->transaction = NULL; trace_binder_transaction_update_buffer_release(buffer); - binder_release_entire_buffer(proc, NULL, buffer, false); + binder_release_entire_buffer(proc, NULL, buffer, true); binder_alloc_free_buf(&proc->alloc, buffer); + binder_free_txn_fixups(t_outdated); kfree(t_outdated); binder_stats_deleted(BINDER_STAT_TRANSACTION); } -- 2.55.0.1082.g2b9226bbc0-goog