CVE-2026-64264

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/0483fffdeeb363f320e6bf5fc0f0306007507306
• https://git.kernel.org/stable/c/fe604c08d874648a69187f6380e5c7858627dc04
• https://git.kernel.org/stable/c/3a0a8bc51a13951c5141262bf770eeea3e0b6228

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