binder: fix leaked fd fixups on TF_UPDATE_TXN supersede

Overview

In the Linux kernel, the following vulnerability has been resolved:

binder: fix leaked fd fixups on TF_UPDATE_TXN supersede

When a TF_UPDATE_TXN transaction supersedes a pending async transaction in a frozen process, the outdated transaction is freed with kfree() directly. This skips binder_free_txn_fixups(), leaking all binder_txn_fd_fixup entries and their fget()'d struct file references.

The leaked file refcounts never reach zero, so the struct file objects are permanently pinned in memory. They survive process exit and accumulate across invocations until file-max exhaustion.

Every other transaction cleanup path (binder_free_transaction(), binder_transaction() error paths, binder_release_work()) correctly calls binder_free_txn_fixups(). Add the missing call before kfree() in the t_outdated cleanup block.

Affected

• Linux >= 9864bb4801331daa48514face9d0f4861e4d485b < 7fd609fb0e9dcbc4d7a1e4da1af5368c0555ff55
• Linux >= 9864bb4801331daa48514face9d0f4861e4d485b < 1299cb3fb061598496086fc87ff291057831148e
• Linux >= 9864bb4801331daa48514face9d0f4861e4d485b < 6673f4f21e2fddfed0abe1eb9045cc958e6db130
• Linux >= 9864bb4801331daa48514face9d0f4861e4d485b < c4c02084d6687d5cd5edccaf52cc45e5160f1184
• Linux 6.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.