FAILED: patch "[PATCH] binder: fix UAF in binder_free_transaction()" failed to apply to 5.10-stable tree

FAILED: patch "[PATCH] binder: fix UAF in binder_free_transaction()" failed to apply to 5.10-stable tree

[gregkh]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x f223d27a546c1e1f48d38fd67760e78f068fe8c4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026071359-voyage-hassle-bb34@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f223d27a546c1e1f48d38fd67760e78f068fe8c4 Mon Sep 17 00:00:00 2001
From: Carlos Llamas <cmllamas@google.com>
Date: Fri, 19 Jun 2026 18:52:31 +0000
Subject: [PATCH] binder: fix UAF in binder_free_transaction()

In binder_free_transaction(), the t->to_proc is read under the t->lock.
However, once the t->lock is dropped, the to_proc can die in parallel.
This leads to a use-after-free error when we attempt to acquire its
inner lock right afterwards:

  ==================================================================
  BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x1a0
  Write of size 4 at addr ffff00001125da70 by task B/672

  CPU: 20 UID: 0 PID: 672 Comm: B Not tainted 7.1.0-rc6-00284-g8e65320d91cd #4 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   _raw_spin_lock+0xe4/0x1a0
   binder_free_transaction+0x8c/0x320
   binder_send_failed_reply+0x21c/0x2f8
   binder_thread_release+0x488/0x7e0
   binder_ioctl+0x12c0/0x29a0
  [...]

  Allocated by task 675:
   __kmalloc_cache_noprof+0x174/0x444
   binder_open+0x118/0xb70
   do_dentry_open+0x374/0x1040
   vfs_open+0x58/0x3bc
  [...]

  Freed by task 212:
   __kasan_slab_free+0x58/0x80
   kfree+0x1a0/0x4a4
   binder_proc_dec_tmpref+0x32c/0x5e0
   binder_deferred_func+0xc48/0x104c
   process_one_work+0x53c/0xbc0
  [...]
  ==================================================================

To prevent this, pin the target thread (t->to_thread) to guarantee the
target process remains alive. Undelivered transactions without a target
thread are already safe, as the target process can only be the current
context in those paths.

Cc: stable <stable@kernel.org>
Reported-by: Alice Ryhl <aliceryhl@google.com>
Closes: https://lore.kernel.org/all/aikJKVuny_eOivwN@google.com/
Fixes: a370003cc301 ("binder: fix possible UAF when freeing buffer")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260619185233.2194678-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 013e2bfab070..8f2ef1bd539f 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1658,10 +1658,19 @@ static void binder_txn_latency_free(struct binder_transaction *t)
 
 static void binder_free_transaction(struct binder_transaction *t)
 {
+	struct binder_thread *target_thread;
 	struct binder_proc *target_proc;
 
 	spin_lock(&t->lock);
 	target_proc = t->to_proc;
+	target_thread = t->to_thread;
+	/*
+	 * Pin target_thread to keep target_proc alive. Undelivered
+	 * transactions with !target_thread are safe, as target_proc
+	 * can only be the current context there.
+	 */
+	if (target_thread)
+		atomic_inc(&target_thread->tmp_ref);
 	spin_unlock(&t->lock);
 
 	if (target_proc) {
@@ -1676,6 +1685,10 @@ static void binder_free_transaction(struct binder_transaction *t)
 			t->buffer->transaction = NULL;
 		binder_inner_proc_unlock(target_proc);
 	}
+
+	if (target_thread)
+		binder_thread_dec_tmpref(target_thread);
+
 	if (trace_binder_txn_latency_free_enabled())
 		binder_txn_latency_free(t);
 	/*

[PATCH 5.10.y 1/2] binder: fix UAF in binder_thread_release()

[Sasha Levin]

From: Carlos Llamas <cmllamas@google.com>

[ Upstream commit 114a116aaa5f0295376cdf12da743c5bce3b20ce ]

When a thread exits, binder_thread_release() walks its transaction stack
to clear the t->from and t->to_proc that correspond with the exiting
thread. However, a process dying in parallel might attempt to kfree some
of these transactions. And if one of them has no associated t->to_proc,
the t->to_proc->inner_lock will not be acquired.

This means that transaction accesses in binder_thread_release() after
t->to_proc has been cleared might race with binder_free_transaction()
and cause a use-after-free error as reported by KASAN:

  ==================================================================
  BUG: KASAN: slab-use-after-free in binder_thread_release+0x5d0/0x798
  Write of size 8 at addr ffff000016627500 by task X/715

  CPU: 17 UID: 0 PID: 715 Comm: X Not tainted 7.1.0-rc5-00149-g8fde5d1d47f6 #30 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   binder_thread_release+0x5d0/0x798
   binder_ioctl+0x12c0/0x299c
   [...]

  Allocated by task 717 on cpu 18 at 67.267803s:
   __kasan_kmalloc+0xa0/0xbc
   __kmalloc_cache_noprof+0x174/0x444
   binder_transaction+0x554/0x8150
   binder_thread_write+0xa30/0x4354
   binder_ioctl+0x20f0/0x299c
   [...]

  Freed by task 202 on cpu 18 at 90.416221s:
   __kasan_slab_free+0x58/0x80
   kfree+0x1a0/0x4a4
   binder_free_transaction+0x150/0x294
   binder_send_failed_reply+0x398/0x6d8
   binder_release_work+0x3e4/0x4ec
   binder_deferred_func+0xbd8/0x104c
   [...]
  ==================================================================

In order to avoid this, make sure that binder_free_transaction() reads
the t->to_proc under the transaction lock. This will serialize the
transaction release with the accesses in binder_thread_release(). Plus,
it matches the documented locking rules for @to_proc.

Cc: stable <stable@kernel.org>
Fixes: 7a4408c6bd3e ("binder: make sure accesses to proc/thread are safe")
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://patch.msgid.link/20260619185233.2194678-1-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: f223d27a546c ("binder: fix UAF in binder_free_transaction()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/android/binder.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 9577193e72e64f..eaaa6e86cc5599 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1909,7 +1909,11 @@ static void binder_free_txn_fixups(struct binder_transaction *t)
 
 static void binder_free_transaction(struct binder_transaction *t)
 {
-	struct binder_proc *target_proc = t->to_proc;
+	struct binder_proc *target_proc;
+
+	spin_lock(&t->lock);
+	target_proc = t->to_proc;
+	spin_unlock(&t->lock);
 
 	if (target_proc) {
 		binder_inner_proc_lock(target_proc);
-- 
2.53.0

[PATCH 5.10.y 2/2] binder: fix UAF in binder_free_transaction()

[Sasha Levin]

From: Carlos Llamas <cmllamas@google.com>

[ Upstream commit f223d27a546c1e1f48d38fd67760e78f068fe8c4 ]

In binder_free_transaction(), the t->to_proc is read under the t->lock.
However, once the t->lock is dropped, the to_proc can die in parallel.
This leads to a use-after-free error when we attempt to acquire its
inner lock right afterwards:

  ==================================================================
  BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x1a0
  Write of size 4 at addr ffff00001125da70 by task B/672

  CPU: 20 UID: 0 PID: 672 Comm: B Not tainted 7.1.0-rc6-00284-g8e65320d91cd #4 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   _raw_spin_lock+0xe4/0x1a0
   binder_free_transaction+0x8c/0x320
   binder_send_failed_reply+0x21c/0x2f8
   binder_thread_release+0x488/0x7e0
   binder_ioctl+0x12c0/0x29a0
  [...]

  Allocated by task 675:
   __kmalloc_cache_noprof+0x174/0x444
   binder_open+0x118/0xb70
   do_dentry_open+0x374/0x1040
   vfs_open+0x58/0x3bc
  [...]

  Freed by task 212:
   __kasan_slab_free+0x58/0x80
   kfree+0x1a0/0x4a4
   binder_proc_dec_tmpref+0x32c/0x5e0
   binder_deferred_func+0xc48/0x104c
   process_one_work+0x53c/0xbc0
  [...]
  ==================================================================

To prevent this, pin the target thread (t->to_thread) to guarantee the
target process remains alive. Undelivered transactions without a target
thread are already safe, as the target process can only be the current
context in those paths.

Cc: stable <stable@kernel.org>
Reported-by: Alice Ryhl <aliceryhl@google.com>
Closes: https://lore.kernel.org/all/aikJKVuny_eOivwN@google.com/
Fixes: a370003cc301 ("binder: fix possible UAF when freeing buffer")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260619185233.2194678-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/android/binder.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index eaaa6e86cc5599..233deb4d55daef 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1909,10 +1909,19 @@ static void binder_free_txn_fixups(struct binder_transaction *t)
 
 static void binder_free_transaction(struct binder_transaction *t)
 {
+	struct binder_thread *target_thread;
 	struct binder_proc *target_proc;
 
 	spin_lock(&t->lock);
 	target_proc = t->to_proc;
+	target_thread = t->to_thread;
+	/*
+	 * Pin target_thread to keep target_proc alive. Undelivered
+	 * transactions with !target_thread are safe, as target_proc
+	 * can only be the current context there.
+	 */
+	if (target_thread)
+		atomic_inc(&target_thread->tmp_ref);
 	spin_unlock(&t->lock);
 
 	if (target_proc) {
@@ -1921,6 +1930,10 @@ static void binder_free_transaction(struct binder_transaction *t)
 			t->buffer->transaction = NULL;
 		binder_inner_proc_unlock(target_proc);
 	}
+
+	if (target_thread)
+		binder_thread_dec_tmpref(target_thread);
+
 	/*
 	 * If the transaction has no target_proc, then
 	 * t->buffer->transaction has already been cleared.
-- 
2.53.0