binder_validate_fixup(9)

✨ NAME ✨

Okay bestie, welcome to binder_validate_fixup(9) in the Kernel API Manual. The function is binder_validate_fixup - validates pointer/fd fixups happen in order. That's the name, that's the purpose, periodt. 💅

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🌸 SYNOPSIS 🌸

bool binder_validate_fixup (struct binder_proc *proc , struct
binder_buffer *b , binder_size_t objects_start_offset , binder_size_t
buffer_obj_offset , binder_size_t fixup_offset , binder_size_t
last_obj_offset , binder_size_t last_min_offset );

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🎀 ARGUMENTS 🎀

• proc — the binder_proc owning the buffer. It's giving owner energy. 👑
• b — the transaction buffer, aka the buffer in question.
• objects_start_offset — offset to start of objects buffer.
• buffer_obj_offset — offset to binder_buffer_object in which to fix up.
• fixup_offset — start offset in buffer to fix up.
• last_obj_offset — offset to last binder_buffer_object that we fixed.
• last_min_offset — minimum fixup offset in object at last_obj_offset.

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💖 RETURN 💖

It returns a bool, and the answer is true if a fixup in buffer buffer at offset offset is allowed. Slay. ✅

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🦋 DESCRIPTION 🦋

For safety reasons — yes, safety bestie, this is not a drill — we only allow fixups inside a buffer to happen at increasing offsets. Additionally, we only allow fixup on the last buffer object that was verified, or one of its parents. That's the rule, no cap. 🔥

Example of what is allowed:

A B (parent = A, offset = 0) C (parent = A, offset = 16) D (parent = C, offset = 0) E (parent = A, offset = 32) // min_offset is 16 (C.parent_offset)

Examples of what is not allowed:

Decreasing offsets within the same parent:

A C (parent = A, offset = 16) B (parent = A, offset = 0) // decreasing offset within A

Referring to a parent that wasn't the last object or any of its parents:

A B (parent = A, offset = 0) C (parent = A, offset = 0) C (parent = A, offset = 16) D (parent = B, offset = 0) // B is not A or any of A's parents

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👑 SEE ALSO 👑

Kernel file ./drivers/android/binder.c is the home base, and the whole binder squad is here:

• binder_proc_lock(9)
• binder_proc_unlock(9)
• binder_inner_proc_lock(9)
• binder_inner_proc_unlock(9)
• binder_node_lock(9)
• binder_node_unlock(9)
• binder_node_inner_lock(9)
• binder_node_inner_unlock(9)
• binder_worklist_empty(9)
• binder_enqueue_work_ilocked(9)
• binder_enqueue_deferred_thread_work_ilocked(9)
• binder_enqueue_thread_work_ilocked(9)
• binder_enqueue_thread_work(9)
• binder_dequeue_work(9)
• binder_select_thread_ilocked(9)
• binder_wakeup_thread_ilocked(9)
• binder_inc_node_tmpref(9)
• binder_dec_node_tmpref(9)
• binder_get_ref_for_node_olocked(9)
• binder_inc_ref_olocked(9)
• binder_dec_ref_olocked(9)
• binder_get_node_from_ref(9)
• binder_free_ref(9)
• binder_update_ref_for_handle(9)
• binder_dec_ref_for_handle(9)
• binder_inc_ref_for_node(9)
• binder_thread_dec_tmpref(9)
• binder_proc_dec_tmpref(9)
• binder_get_txn_from(9)
• binder_get_txn_from_and_acq_inner(9)
• binder_free_txn_fixups(9)
• binder_cleanup_transaction(9)
• binder_get_object(9)
• binder_validate_ptr(9)
• struct binder_task_work_cb(9)
• binder_do_fd_close(9)
• binder_deferred_fd_close(9)
• struct binder_ptr_fixup(9)
• struct binder_sg_copy(9)
• binder_do_deferred_txn_copies(9)
• binder_cleanup_deferred_txn_lists(9)
• binder_defer_copy(9)
• binder_add_fixup(9)
• binder_can_update_transaction(9)
• binder_find_outdated_transaction_ilocked(9)
• binder_proc_transaction(9)
• binder_get_node_refs_for_txn(9)
• binder_netlink_report(9)
• binder_free_buf(9)
• binder_apply_fd_fixups(9)
• print_next_binder_node_ilocked(9)

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Signed off from the ./drivers/android source corner, stamped October 2026, still serving binder_validate_fixup(9) realness — mwah 💋✨