[PATCH 5.10 05/41] binderfs: fix ida_alloc_max() upper bound

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Carlos Llamas <cmllamas@google.com>

commit ec4ddc90d201d09ef4e4bef8a2c6d9624525ad68 upstream.

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@vger.kernel.org
Fixes: 3ad20fe393b3 ("binder: implement binderfs")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://patch.msgid.link/20260127235545.2307876-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/android/binderfs.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -122,8 +122,8 @@ static int binderfs_binder_device_create
 	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;
@@ -423,8 +423,8 @@ static int binderfs_binder_ctl_create(st
 	/* 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) {