fuse: Initialize beyond-EOF page contents before setting uptodate

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fuse: Initialize beyond-EOF page contents before setting uptodate fuse_notify_store(), unlike fuse_do_readpage(), does not enable page zeroing (because it can be used to change partial page contents). So fuse_notify_store() must be more careful to fully initialize page contents (including parts of the page that are beyond end-of-file) before marking the page uptodate. The current code can leave beyond-EOF page contents uninitialized, which makes these uninitialized page contents visible to userspace via mmap(). This is an information leak, but only affects systems which do not enable init-on-alloc (via CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y or the corresponding kernel command line parameter).

References

• https://git.kernel.org/stable/c/49934861514d36d0995be8e81bb3312a499d8d9a
• https://git.kernel.org/stable/c/33168db352c7b56ae18aa55c2cae1a1c5905d30e
• https://git.kernel.org/stable/c/4690e2171f651e2b415e3941ce17f2f7b813aff6
• https://git.kernel.org/stable/c/8c78303eafbf85a728dd84d1750e89240c677dd9
• https://git.kernel.org/stable/c/831433527773e665bdb635ab5783d0b95d1246f4
• https://git.kernel.org/stable/c/ac42e0f0eb66af966015ee33fd355bc6f5d80cd6
• https://git.kernel.org/stable/c/18a067240817bee8a9360539af5d79a4bf5398a5
• https://git.kernel.org/stable/c/3c0da3d163eb32f1f91891efaade027fa9b245b9
• https://project-zero.issues.chromium.org/issues/42451729