CVE-2026-72095: dma-fence: Make dma_fence_dedup_array() robust against 0-count input

CVE-2026-72095: dma-fence: Make dma_fence_dedup_array() robust against 0-count input

[Greg Kroah-Hartman]

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

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

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

dma-fence: Make dma_fence_dedup_array() robust against 0-count input

dma_fence_dedup_array() returns 1 when called with num_fences == 0:
the for-loop body never executes, j stays at 0, and the final
`return ++j` yields 1. This contradicts both the kernel-doc ("Return:
Number of unique fences remaining in the array") and the natural
expectation that 0 input gives 0 output.

The caller __dma_fence_unwrap_merge() bails out via the
`if (count == 0 || count == 1)` fast path and so is save.

But amdgpu_userq_wait_*() could reach the dedup call with a zero local
count and dereference an uninitialized fence slot in the array.

Make the contract match the documentation by returning 0 early. This
also skips an unnecessary sort() call on an empty array.

The Linux kernel CVE team has assigned CVE-2026-72095 to this issue.


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

	Issue introduced in 6.16 with commit 575ec9b0c2f11f40535ea737ed5a64792780d1ef and fixed in 6.18.40 with commit 7aa8f3dba53422465dbe1be8dbb7240304462bb2
	Issue introduced in 6.16 with commit 575ec9b0c2f11f40535ea737ed5a64792780d1ef and fixed in 7.1.5 with commit e2d9a2ea178a5da0b4a6693e8ebca5c7fc4d7051
	Issue introduced in 6.16 with commit 575ec9b0c2f11f40535ea737ed5a64792780d1ef and fixed in 7.2-rc2 with commit 77a9298741f8f9e8b963c977f5582ab21c6d3427

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-2026-72095
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/dma-buf/dma-fence-unwrap.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/7aa8f3dba53422465dbe1be8dbb7240304462bb2
	https://git.kernel.org/stable/c/e2d9a2ea178a5da0b4a6693e8ebca5c7fc4d7051
	https://git.kernel.org/stable/c/77a9298741f8f9e8b963c977f5582ab21c6d3427