linux-kernel - [PATCH 2/2] binderfs: fix ida_alloc

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Message-ID: <20260127235545.2307876-2-cmllamas@google.com>
Date: Tue, 27 Jan 2026 23:55:11 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, 
	Christian Brauner <brauner@...nel.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Alice Ryhl <aliceryhl@...gle.com>
Cc: kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org, Todd Kjos <tkjos@...gle.com>
Subject: [PATCH 2/2] binderfs: fix ida_alloc_max() upper bound

The 'max' argument of ida_alloc_max() takes the maximum valid ID and not
the "count". Using an ID of BINDERFS_MAX_MINOR (1 << 20) for dev->minor
would exceed the limits of minor numbers (20-bits). Fix this off-by-one
error by subtracting 1 from the 'max'.

Cc: stable@...r.kernel.org
Fixes: 3ad20fe393b3 ("binder: implement binderfs")
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
 drivers/android/binderfs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index b46bcb91072d..9f8a18c88d66 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -132,8 +132,8 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
 	mutex_lock(&binderfs_minors_mutex);
 	if (++info->device_count <= info->mount_opts.max)
 		minor = ida_alloc_max(&binderfs_minors,
-				      use_reserve ? BINDERFS_MAX_MINOR :
-						    BINDERFS_MAX_MINOR_CAPPED,
+				      use_reserve ? BINDERFS_MAX_MINOR - 1 :
+						    BINDERFS_MAX_MINOR_CAPPED - 1,
 				      GFP_KERNEL);
 	else
 		minor = -ENOSPC;
@@ -408,8 +408,8 @@ static int binderfs_binder_ctl_create(struct super_block *sb)
 	/* Reserve a new minor number for the new device. */
 	mutex_lock(&binderfs_minors_mutex);
 	minor = ida_alloc_max(&binderfs_minors,
-			      use_reserve ? BINDERFS_MAX_MINOR :
-					    BINDERFS_MAX_MINOR_CAPPED,
+			      use_reserve ? BINDERFS_MAX_MINOR - 1 :
+					    BINDERFS_MAX_MINOR_CAPPED - 1,
 			      GFP_KERNEL);
 	mutex_unlock(&binderfs_minors_mutex);
 	if (minor < 0) {
-- 
2.52.0.457.g6b5491de43-goog