[PATCH] remoteproc: core: Do not put the device when device_add() fails

[Yuqiang Sun <izaiahsun@gmail.com>]

When device_add() fails, rproc_add() calls put_device() and then
removes the character device.  The reference it drops is the one
rproc_alloc() took with device_initialize(), which belongs to the
caller: after a failed rproc_add(), every driver frees the rproc,
either with rproc_free() or through devm_rproc_alloc(), and both drop
that reference again.

So the rproc is freed inside rproc_add(): by the put_device() itself,
or, with CONFIG_REMOTEPROC_CDEV, by the cdev_del() that follows, when
the character device drops its reference on the parent device.  The
caller then uses the freed rproc and puts it a second time.

With one allocation failure injected into device_add() (failslab
restricted to rproc_add) while st_fdma probes, KASAN reports:

  BUG: KASAN: slab-use-after-free in slim_clk_disable+0x38/0xf4 [st_slim_rproc]
  Read of size 8 by task insmod/69
  Call trace:
   slim_clk_disable
   st_slim_rproc_alloc
   st_fdma_probe
  Freed by task 69:
   kfree
   rproc_type_release
   device_release
   kobject_put
   cdev_default_release
   kobject_put
   cdev_del
   rproc_char_device_remove
   rproc_add
   st_slim_rproc_alloc

followed by use-after-free reports in kobject_put() and
refcount_warn_saturate() from the rproc_free() in
st_slim_rproc_alloc().

Remove the put_device(): the caller's rproc_free() drops the reference
and releases the rproc, as it does for the other failures in
rproc_add().

The problem was found with kbound, a static analysis prototype that
checks whether callers rely on an object after a callee returns a value
for which the callee may have released it, on v7.2.12; it is present
in rproc-next.

Build-tested with x86_64 and arm64 allmodconfig (W=1, sparse): no new
warnings.  Run-tested on QEMU's arm64 virt machine (TCG) with KASAN,
using a device tree node for an ST FDMA with a SLIM core, so that
st_fdma_probe() reaches rproc_add() without the hardware (no clocks,
MMIO windows only mapped), and failing each allocation in rproc_add()
in turn with failslab: before this patch every failure in device_add()
(9 of 9) gives the reports above; with it nothing is reported, and the
rproc is released once, by rproc_free().  Not tested on remoteproc
hardware.

Fixes: 7dbdb8bd7c02 ("remoteproc: core: Cleanup device in case of failure")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5-5 kbound
Signed-off-by: Yuqiang Sun <izaiahsun@gmail.com>
---
 drivers/remoteproc/remoteproc_core.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
index b88bf179507d..e4f44a3c8b4d 100644
--- a/drivers/remoteproc/remoteproc_core.c
+++ b/drivers/remoteproc/remoteproc_core.c
@@ -2309,10 +2309,8 @@ int rproc_add(struct rproc *rproc)
 		return ret;
 
 	ret = device_add(dev);
-	if (ret < 0) {
-		put_device(dev);
+	if (ret < 0)
 		goto rproc_remove_cdev;
-	}
 
 	dev_info(dev, "%s is available\n", rproc->name);
 

base-commit: 82d0bbd67c42a44f0e18b0b7b0da0f3ace0c9527
-- 
2.53.0