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Alice Ryhl 598fe3ff32 rust_binder: correctly handle FDA objects of length zero 
commit 8f589c9c3b upstream.

Fix a bug where an empty FDA (fd array) object with 0 fds would cause an
out-of-bounds error. The previous implementation used `skip == 0` to
mean "this is a pointer fixup", but 0 is also the correct skip length
for an empty FDA. If the FDA is at the end of the buffer, then this
results in an attempt to write 8-bytes out of bounds. This is caught and
results in an EINVAL error being returned to userspace.

The pattern of using `skip == 0` as a special value originates from the
C-implementation of Binder. As part of fixing this bug, this pattern is
replaced with a Rust enum.

I considered the alternate option of not pushing a fixup when the length
is zero, but I think it's cleaner to just get rid of the zero-is-special
stuff.

The root cause of this bug was diagnosed by Gemini CLI on first try. I
used the following prompt:

> There appears to be a bug in @drivers/android/binder/thread.rs where
> the Fixups oob bug is triggered with 316 304 316 324. This implies
> that we somehow ended up with a fixup where buffer A has a pointer to
> buffer B, but the pointer is located at an index in buffer A that is
> out of bounds. Please investigate the code to find the bug. You may
> compare with @drivers/android/binder.c that implements this correctly.

Cc: stable@vger.kernel.org
Reported-by: DeepChirp <DeepChirp@outlook.com>
Closes: https://github.com/waydroid/waydroid/issues/2157
Fixes: eafedbc7c0 ("rust_binder: add Rust Binder driver")
Tested-by: DeepChirp <DeepChirp@outlook.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://patch.msgid.link/20251229-fda-zero-v1-1-58a41cb0e7ec@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-02-11 13:41:45 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.