From: Robert Richter rrichter@marvell.com
[ Upstream commit 16214bd9e43a31683a7073664b000029bba00354 ]
The following warning from the refcount framework is seen during ghes initialization:
EDAC MC0: Giving out device to module ghes_edac.c controller ghes_edac: DEV ghes (INTERRUPT) ------------[ cut here ]------------ refcount_t: increment on 0; use-after-free. WARNING: CPU: 36 PID: 1 at lib/refcount.c:156 refcount_inc_checked [...] Call trace: refcount_inc_checked ghes_edac_register ghes_probe ...
It warns if the refcount is incremented from zero. This warning is reasonable as a kernel object is typically created with a refcount of one and freed once the refcount is zero. Afterwards the object would be "used-after-free".
For GHES, the refcount is initialized with zero, and that is why this message is seen when initializing the first instance. However, whenever the refcount is zero, the device will be allocated and registered. Since the ghes_reg_mutex protects the refcount and serializes allocation and freeing of ghes devices, a use-after-free cannot happen here.
Instead of using refcount_inc() for the first instance, use refcount_set(). This can be used here because the refcount is zero at this point and can not change due to its protection by the mutex.
Fixes: 23f61b9fc5cc ("EDAC/ghes: Fix locking and memory barrier issues") Reported-by: John Garry john.garry@huawei.com Signed-off-by: Robert Richter rrichter@marvell.com Signed-off-by: Borislav Petkov bp@suse.de Tested-by: John Garry john.garry@huawei.com Cc: huangming23@huawei.com Cc: James Morse james.morse@arm.com Cc: linuxarm@huawei.com Cc: linux-edac linux-edac@vger.kernel.org Cc: Mauro Carvalho Chehab mchehab@kernel.org Cc: tanxiaofei@huawei.com Cc: Tony Luck tony.luck@intel.com Cc: wanghuiqiang@huawei.com Link: https://lkml.kernel.org/r/20191121213628.21244-1-rrichter@marvell.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/edac/ghes_edac.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c index 1858baa96211b..523dd56a798c9 100644 --- a/drivers/edac/ghes_edac.c +++ b/drivers/edac/ghes_edac.c @@ -572,8 +572,8 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev) ghes_pvt = pvt; spin_unlock_irqrestore(&ghes_lock, flags);
- /* only increment on success */ - refcount_inc(&ghes_refcount); + /* only set on success */ + refcount_set(&ghes_refcount, 1);
unlock: mutex_unlock(&ghes_reg_mutex);