CVE-2026-64328: usb: gadget: f_fs: Fix DMA fence leak

From: Greg Kroah-Hartman <[email protected]>

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

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

usb: gadget: f_fs: Fix DMA fence leak

In ffs_dmabuf_transfer(), a ffs_dma_fence object is kmalloc'd, with the
underlying dma_fence later initialized by dma_fence_init(), which sets
its kref counter to 1. Then, dma_resv_add_fence() gets a second
reference, and a pointer to the ffs_dma_fence is passed as the
usb_request's "context" field.

The dma-resv mechanism will manage the second reference, but the first
reference is never properly released; the ffs_dmabuf_cleanup() function
decreases the reference count, but only to balance with the reference
grab in ffs_dmabuf_signal_done().

The code will then slowly leak memory as more ffs_dma_fence objects are
created without being ever freed.

Address this issue by transferring ownership of the fence to the DMA
reservation object, by calling dma_fence_put() right after
dma_resv_add_fence(). The ffs_dma_fence then gets properly discarded
after being signalled.

The Linux kernel CVE team has assigned CVE-2026-64328 to this issue.


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

	Issue introduced in 6.9 with commit 7b07a2a7ca02a20124b552be96c5a56910795488 and fixed in 6.12.96 with commit b7475b2dce5e121e687280ba5732ccefe77ffd2f
	Issue introduced in 6.9 with commit 7b07a2a7ca02a20124b552be96c5a56910795488 and fixed in 6.18.39 with commit e086c16962a1b0142e2675610e9c06fcfcd4c3a8
	Issue introduced in 6.9 with commit 7b07a2a7ca02a20124b552be96c5a56910795488 and fixed in 7.1.4 with commit 0cae3d6109427c455bad0a18dfb3e2a91657e38a
	Issue introduced in 6.9 with commit 7b07a2a7ca02a20124b552be96c5a56910795488 and fixed in 7.2-rc3 with commit baa6b6068a3f2bf2ed525a1cb37975905dadc658

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-2026-64328
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:
	drivers/usb/gadget/function/f_fs.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/b7475b2dce5e121e687280ba5732ccefe77ffd2f
	https://git.kernel.org/stable/c/e086c16962a1b0142e2675610e9c06fcfcd4c3a8
	https://git.kernel.org/stable/c/0cae3d6109427c455bad0a18dfb3e2a91657e38a
	https://git.kernel.org/stable/c/baa6b6068a3f2bf2ed525a1cb37975905dadc658