CVE-2026-64264: fuse-uring: fix EFAULT clobber in fuse_uring_commit

CVE-2026-64264: fuse-uring: fix EFAULT clobber in fuse_uring_commit

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

fuse-uring: fix EFAULT clobber in fuse_uring_commit

copy_from_user() returns the number of bytes not copied as an unsigned
residual on failure (1..sizeof(struct fuse_out_header)). fuse_uring_commit
stores that residual in ssize_t err, sets req->out.h.error to -EFAULT,
then jumps to out: with err still holding the positive residual.

    err = copy_from_user(&req->out.h, &ent->headers->in_out,
                         sizeof(req->out.h));
    if (err) {
        req->out.h.error = -EFAULT;
        goto out;          /* err is the positive residual */
    }
    ...
    out:
        fuse_uring_req_end(ent, req, err);

fuse_uring_req_end() then runs

    if (error)
        req->out.h.error = error;

which overwrites the just-assigned -EFAULT with the positive residual.
FUSE callers such as fuse_simple_request() test err < 0 to detect
failure, so the positive value is interpreted as success and the
caller proceeds with an uninitialised or partial req->out.args.

Fix by assigning err = -EFAULT in the failure branch before jumping
to out, so fuse_uring_req_end() receives a negative errno and sets
req->out.h.error to -EFAULT.

The Linux kernel CVE team has assigned CVE-2026-64264 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 6.18.39 with commit 0483fffdeeb363f320e6bf5fc0f0306007507306
	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 7.1.4 with commit fe604c08d874648a69187f6380e5c7858627dc04
	Issue introduced in 6.14 with commit c090c8abae4b6b77a1bee116aa6c385456ebef96 and fixed in 7.2-rc1 with commit 3a0a8bc51a13951c5141262bf770eeea3e0b6228

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64264
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/fuse/dev_uring.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/0483fffdeeb363f320e6bf5fc0f0306007507306
	https://git.kernel.org/stable/c/fe604c08d874648a69187f6380e5c7858627dc04
	https://git.kernel.org/stable/c/3a0a8bc51a13951c5141262bf770eeea3e0b6228