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It wraps open-coded kref_get_unless_zero() and asserts that dma_list_mutex is held, matching its put counterpart. No functional change intended. Suggested-by: Frank Li Signed-off-by: Shivank Garg Reviewed-by: Logan Gunthorpe --- drivers/dma/dmaengine.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 6ffd8bd82154..77638dc16e71 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -433,6 +433,12 @@ static void dma_device_release(struct kref *ref) device->device_release(device); } =20 +static bool dma_device_get(struct dma_device *device) +{ + lockdep_assert_held(&dma_list_mutex); + return kref_get_unless_zero(&device->ref); +} + static void dma_device_put(struct dma_device *device) { lockdep_assert_held(&dma_list_mutex); @@ -460,8 +466,7 @@ static int dma_chan_get(struct dma_chan *chan) if (!try_module_get(owner)) return -ENODEV; =20 - ret =3D kref_get_unless_zero(&chan->device->ref); - if (!ret) { + if (!dma_device_get(chan->device)) { ret =3D -ENODEV; goto module_put_out; } --=20 2.43.0 From nobody Mon Sep 28 20:05:01 2026 Received: from MW6PR02CU001.outbound.protection.outlook.com (mail-westus2azon11012026.outbound.protection.outlook.com [52.101.48.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E2393BB135; 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Mon, 17 Aug 2026 22:45:23 -0500 From: Shivank Garg Date: Tue, 18 Aug 2026 03:43:46 +0000 Subject: [PATCH v4 2/4] dmaengine: Fix device kref underflow in dma_chan_put() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20260818-dmaengine-kref-fix-v4-2-c6ef991462a0@amd.com> References: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> In-Reply-To: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" , Andrew Morton CC: , , , Shivank Garg , Frank Li X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787024717; l=1590; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=WyK1bhlIzw10xQpX3eRtqRomlgut0wJwNB8bjK+3rHk=; b=UpYw6uNXUfg6ea1Mtmu5CQCcTS2RTx12IM/nV2Khqjaj3aEujOGyz8i5jgeKC9mOQA/gLSbzm H7hJvqR/QqvB/cDJ2R57hpZcvN60ZHxW0XyJ+tVpliv3kePxdV0n30b X-Developer-Key: i=shivankg@amd.com; 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chan->client_count++; return 0; } if (!try_module_get(owner)) return -ENODEV; if (!dma_device_get(chan->device)) { // calls kref_get_unless_zero() dma_chan_put() drops the ref unconditionally, so every fast-path get/put pair drops one extra device reference. The bug fires when two conditions hold together: a non-private provider has a persistent client holding chan->client_count > 0 and another client cycles dmaengine_get()/dmaengine_put(). When the kref hits zero, the subsequent dma_find_channel() returns NULL even though the provider module is still loaded. Fix this by dropping device->ref only on the last put, matching the single slow-path get. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struc= t") Reviewed-by: Frank Li Signed-off-by: Shivank Garg Reviewed-by: Logan Gunthorpe --- drivers/dma/dmaengine.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 77638dc16e71..3ae53e11e54a 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -520,7 +520,9 @@ static void dma_chan_put(struct dma_chan *chan) chan->route_data =3D NULL; } =20 - dma_device_put(chan->device); + /* This channel is not in use anymore, drop the device ref */ + if (!chan->client_count) + dma_device_put(chan->device); module_put(dma_chan_to_owner(chan)); } =20 --=20 2.43.0 From nobody Mon Sep 28 20:05:01 2026 Received: from MW6PR02CU001.outbound.protection.outlook.com (mail-westus2azon11012016.outbound.protection.outlook.com [52.101.48.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B05F23A9002; 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Mon, 17 Aug 2026 22:45:26 -0500 From: Shivank Garg Date: Tue, 18 Aug 2026 03:43:47 +0000 Subject: [PATCH v4 3/4] dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20260818-dmaengine-kref-fix-v4-3-c6ef991462a0@amd.com> References: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> In-Reply-To: <20260818-dmaengine-kref-fix-v4-0-c6ef991462a0@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" , Andrew Morton CC: , , , Shivank Garg , Sashiko , Frank Li X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787024717; l=1879; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=Koho1l38UfCu/XdwxrWn8BVFGPIbDQXwrLQ8b7LWG4s=; b=tXjLUM9a/6QI4iDCvQ4OSWRaohI+PjGMkY3xYVpUWJcogZiQ5HEpJ1dDjLL8j73iSJfpNMI4W 0HJEAIv10iBADyd1S/vDD4N5pzq1WpRn4iLwAlZeCin+F38F8Sf4y58 X-Developer-Key: i=shivankg@amd.com; 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KASAN catches it: slab-use-after-free in dma_chan_put+0x3e6/0x4c0 Read of size 8 by task insmod/6319 Freed by task 6319: kfree+0x225/0x470 dma_chan_put+0x395/0x4c0 dmaengine_put+0xf8/0x160 Cache the module owner in dma_chan_put() before the put so the trailing module_put() does not need chan->device. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struc= t") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d612= 5048fb7@amd.com Reviewed-by: Frank Li Signed-off-by: Shivank Garg Reviewed-by: Logan Gunthorpe --- drivers/dma/dmaengine.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 3ae53e11e54a..d075051dd187 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -500,10 +500,13 @@ static int dma_chan_get(struct dma_chan *chan) */ static void dma_chan_put(struct dma_chan *chan) { + struct module *owner; + /* This channel is not in use, bail out */ if (!chan->client_count) return; =20 + owner =3D dma_chan_to_owner(chan); chan->client_count--; =20 /* This channel is not in use anymore, free it */ @@ -523,7 +526,7 @@ static void dma_chan_put(struct dma_chan *chan) /* This channel is not in use anymore, drop the device ref */ if (!chan->client_count) dma_device_put(chan->device); 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Because there is no grace period between unlinking the device and freeing it, concurrent RCU readers in dma_issue_pending_all() can access the device after it has been freed. The lockless walk originally relied on clients holding a dmaengine reference to pin the provider module, and therefore the device, for as long as they might traverse the list. Commit 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") decoupled the dma_device lifetime from the module reference, so the device can now be released while a reader is still walking the list. Add synchronize_rcu() before the device is freed, so RCU readers are guaranteed to have finished. Keep it unconditional: providers that do not implement device_release() free the device themselves once dma_async_device_unregister() returns, so they need the same grace period. Fixes: 2ba05622b8b1 ("dmaengine: provide a common 'issue_pending_all' imple= mentation") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260526-dmaengine-kref-fix-v2-0-3df60= afac01d@amd.com Reviewed-by: Frank Li Signed-off-by: Shivank Garg Reviewed-by: Logan Gunthorpe --- drivers/dma/dmaengine.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index d075051dd187..604c9af19936 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -429,6 +429,12 @@ static void dma_device_release(struct kref *ref) list_del_rcu(&device->global_node); dma_channel_rebalance(); =20 + /* + * Wait for RCU readers (e.g. dma_issue_pending_all()) that may still + * be traversing dma_device_list before the device is freed. + */ + synchronize_rcu(); + if (device->device_release) device->device_release(device); } --=20 2.43.0