rust_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@vger.kernel.org
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202512181203.IOv6IChH-lkp@intel.com/
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260127235545.2307876-1-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder/rust_binderfs.c b/drivers/android/binder/rust_binderfs.c
index c69026df775c2581562103c56abbf22159ac1380..88374b31ab7c1177bb19c7795b28a3065d74af43 100644 (file)
--- a/drivers/android/binder/rust_binderfs.c
+++ b/drivers/android/binder/rust_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;
@@ -405,8 +405,8 @@ 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) {