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([2402:e280:3d9e:537:8ccb:550c:e84d:a5b1]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-34726696ba5sm7287600a91.2.2025.11.21.22.12.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Nov 2025 22:12:33 -0800 (PST) From: Sameeksha Sankpal To: mchehab@kernel.org Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Sameeksha Sankpal , syzbot+d445a71e1c011b592c16@syzkaller.appspotmail.com Subject: [PATCH] media: dvb-core: fix use-after-free in dvb_device_open() error path Date: Sat, 22 Nov 2025 11:42:25 +0530 Message-ID: <20251122061225.47432-1-sameekshasankpal@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" syzbot reported a slab-use-after-free in dvb_device_put() triggered when opening a DVB device fails during the device-specific ->open() callback. The root cause is a reference counting imbalance in dvb_device_open(). The code assigns a dvb_device pointer to file->private_data after calling dvb_device_get(), but if the subsequent ->open() call fails, the error path drops the reference with dvb_device_put() and returns an error. However, the VFS layer will still call ->release() on the file, and dvb_device_release() will call dvb_device_put() again on file->private_data. Since the earlier put() already freed the device, the release() path ends up operating on freed memory, leading to a use-after-free. Fix this by explicitly taking a reference for the file descriptor and letting the ->release() method drop it, while the error path only drops the reference acquired for the open logic. This ensures that the device remains alive until VFS calls ->release(), regardless of ->open() failure. Reported-by: syzbot+d445a71e1c011b592c16@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dd445a71e1c011b592c16 Signed-off-by: Sameeksha Sankpal --- drivers/media/dvb-core/dvbdev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbde= v.c index 9df7c213716a..7fdc21a770a3 100644 --- a/drivers/media/dvb-core/dvbdev.c +++ b/drivers/media/dvb-core/dvbdev.c @@ -103,7 +103,8 @@ static int dvb_device_open(struct inode *inode, struct = file *file) new_fops =3D fops_get(dvbdev->fops); if (!new_fops) goto fail; - file->private_data =3D dvb_device_get(dvbdev); + dvb_device_get(dvbdev); + file->private_data =3D dvbdev; replace_fops(file, new_fops); if (file->f_op->open) err =3D file->f_op->open(inode, file); --=20 2.43.0