From: Alessandro Carminati acarmina@redhat.com
[ Upstream commit ca46946a482238b0cdea459fb82fc837fb36260e ]
Failing to reset coupling_desc.n_coupled after freeing coupled_rdevs can lead to NULL pointer dereference when regulators are accessed post-unbind.
This can happen during runtime PM or other regulator operations that rely on coupling metadata.
For example, on ridesx4, unbinding the 'reg-dummy' platform device triggers a panic in regulator_lock_recursive() due to stale coupling state.
Ensure n_coupled is set to 0 to prevent access to invalid pointers.
Signed-off-by: Alessandro Carminati acarmina@redhat.com Link: https://patch.msgid.link/20250626083809.314842-1-acarmina@redhat.com Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
Now I understand the bug. After unbind, the regulator_dev structure may still exist and be accessed (e.g., during runtime PM operations). If n_coupled is not reset to 0, code like regulator_lock_recursive() will try to iterate through n_coupled entries in the coupled_rdevs array, but that array has been freed and set to NULL, causing a NULL pointer dereference.
**YES**
This commit should be backported to stable kernel trees for the following reasons:
1. **It fixes a real NULL pointer dereference bug**: The commit addresses a crash that occurs when regulators are accessed after unbind. The issue is in `regulator_lock_recursive()` at line 326-327 where it iterates through `n_coupled` entries in the `coupled_rdevs` array: ```c for (i = 0; i < rdev->coupling_desc.n_coupled; i++) { c_rdev = rdev->coupling_desc.coupled_rdevs[i]; ``` If `n_coupled > 0` but `coupled_rdevs` has been freed (set to NULL), this causes a NULL pointer dereference.
2. **The fix is minimal and safe**: The patch adds just one line: ```c rdev->coupling_desc.n_coupled = 0; ``` This ensures that after freeing the coupling data, the count is also reset, preventing any code from trying to access the freed array.
3. **It affects a critical subsystem**: The regulator framework is essential for power management, and crashes in this subsystem can cause system instability or complete failure.
4. **The bug can be triggered during normal operations**: The commit message mentions this happens during runtime PM or other regulator operations, which are common scenarios, not edge cases.
5. **Similar to other backported fixes**: Looking at the historical commits, we see that similar coupling-related fixes have been backported: - "regulator: core: Release coupled_rdevs on regulator_init_coupling() error" (backported) - "regulator: da9063: fix null pointer deref with partial DT config" (backported) These precedents show that NULL pointer fixes in the regulator subsystem are considered important for stable trees.
6. **Clear reproducer**: The commit mentions a specific platform (ridesx4) where unbinding the 'reg-dummy' platform device triggers the panic, indicating this is a reproducible issue.
The fix follows the stable kernel rules: it's a small, contained fix for an important bug with minimal risk of regression.
drivers/regulator/core.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c index 90629a7566932..4ecad5c6c8390 100644 --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -5639,6 +5639,7 @@ static void regulator_remove_coupling(struct regulator_dev *rdev) ERR_PTR(err)); }
+ rdev->coupling_desc.n_coupled = 0; kfree(rdev->coupling_desc.coupled_rdevs); rdev->coupling_desc.coupled_rdevs = NULL; }