The bug is here: dev = new_dev->dev;
The list iterator 'new_dev' will point to a bogus position containing HEAD if the list is empty or no element is found. This case must be checked before any use of the iterator, otherwise it will lead to a invalid memory access.
To fix this bug, add an check. Use a new variable 'iter' as the list iterator, while use the old variable 'new_dev' as a dedicated pointer to point to the found element.
Cc: stable@vger.kernel.org Fixes: deaa51465105a ("PM / OPP: Add debugfs support") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com --- drivers/opp/debugfs.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c index 596c185b5dda..a4476985e4ce 100644 --- a/drivers/opp/debugfs.c +++ b/drivers/opp/debugfs.c @@ -187,14 +187,19 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table) static void opp_migrate_dentry(struct opp_device *opp_dev, struct opp_table *opp_table) { - struct opp_device *new_dev; + struct opp_device *new_dev = NULL, *iter; const struct device *dev; struct dentry *dentry;
/* Look for next opp-dev */ - list_for_each_entry(new_dev, &opp_table->dev_list, node) - if (new_dev != opp_dev) + list_for_each_entry(iter, &opp_table->dev_list, node) + if (iter != opp_dev) { + new_dev = iter; break; + } + + if (!new_dev) + return;
/* new_dev is guaranteed to be valid here */ dev = new_dev->dev;
On 27-03-22, 13:39, Xiaomeng Tong wrote:
The bug is here: dev = new_dev->dev;
The list iterator 'new_dev' will point to a bogus position containing HEAD if the list is empty or no element is found. This case must be checked before any use of the iterator, otherwise it will lead to a invalid memory access.
To fix this bug, add an check. Use a new variable 'iter' as the list iterator, while use the old variable 'new_dev' as a dedicated pointer to point to the found element.
Cc: stable@vger.kernel.org Fixes: deaa51465105a ("PM / OPP: Add debugfs support") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com
drivers/opp/debugfs.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c index 596c185b5dda..a4476985e4ce 100644 --- a/drivers/opp/debugfs.c +++ b/drivers/opp/debugfs.c @@ -187,14 +187,19 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table) static void opp_migrate_dentry(struct opp_device *opp_dev, struct opp_table *opp_table) {
- struct opp_device *new_dev;
- struct opp_device *new_dev = NULL, *iter; const struct device *dev; struct dentry *dentry;
/* Look for next opp-dev */
- list_for_each_entry(new_dev, &opp_table->dev_list, node)
if (new_dev != opp_dev)
- list_for_each_entry(iter, &opp_table->dev_list, node)
if (iter != opp_dev) {new_dev = iter; break;}- if (!new_dev)
return;
I think you missed this check in the parent function ?
if (!list_is_singular(&opp_table->dev_list)) {
i.e. this bug can never happen.
On Mon, 28 Mar 2022 08:47:39 +0530, Viresh Kumar wrote:
diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c index 596c185b5dda..a4476985e4ce 100644 --- a/drivers/opp/debugfs.c +++ b/drivers/opp/debugfs.c @@ -187,14 +187,19 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table) static void opp_migrate_dentry(struct opp_device *opp_dev, struct opp_table *opp_table) {
- struct opp_device *new_dev;
- struct opp_device *new_dev = NULL, *iter; const struct device *dev; struct dentry *dentry;
/* Look for next opp-dev */
- list_for_each_entry(new_dev, &opp_table->dev_list, node)
if (new_dev != opp_dev)
- list_for_each_entry(iter, &opp_table->dev_list, node)
if (iter != opp_dev) {new_dev = iter; break;}- if (!new_dev)
return;I think you missed this check in the parent function ?
if (!list_is_singular(&opp_table->dev_list)) {i.e. this bug can never happen.
No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: if (!list_is_singular(&opp_table->dev_list)),
while list_is_singlular is: !list_empty(head) && (head->next == head->prev);
so the condition is: list_empty(head) || (head->next != head->prev)
if the list is empty, the bug can be triggered.
-- Xiaomeng Tong
On 28-03-22, 15:43, Xiaomeng Tong wrote:
No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: if (!list_is_singular(&opp_table->dev_list)),
while list_is_singlular is: !list_empty(head) && (head->next == head->prev);
so the condition is: list_empty(head) || (head->next != head->prev)
if the list is empty, the bug can be triggered.
List can't be empty here by design. It will be a huge bug in that case, which should lead to crash somewhere.
On Mon, 28 Mar 2022 14:20:57 +0530, Viresh Kumar wrote:
On 28-03-22, 15:43, Xiaomeng Tong wrote:
No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: if (!list_is_singular(&opp_table->dev_list)),
while list_is_singlular is: !list_empty(head) && (head->next == head->prev);
so the condition is: list_empty(head) || (head->next != head->prev)
if the list is empty, the bug can be triggered.
List can't be empty here by design. It will be a huge bug in that case, which should lead to crash somewhere.
There is anther condition to trigger this bug: the list is not empty and no element found (if (iter != opp_dev)).
-- Xiaomeng Tong
On 28-03-22, 17:13, Xiaomeng Tong wrote:
On Mon, 28 Mar 2022 14:20:57 +0530, Viresh Kumar wrote:
On 28-03-22, 15:43, Xiaomeng Tong wrote:
No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: if (!list_is_singular(&opp_table->dev_list)),
while list_is_singlular is: !list_empty(head) && (head->next == head->prev);
so the condition is: list_empty(head) || (head->next != head->prev)
if the list is empty, the bug can be triggered.
List can't be empty here by design. It will be a huge bug in that case, which should lead to crash somewhere.
There is anther condition to trigger this bug: the list is not empty and no element found (if (iter != opp_dev)).
I suggest reading the code again, considering opp_debug_unregister() as well.
What's happening here is this:
- Several devices share the OPP table. - One of them (devX) is going away and opp_debug_unregister() is called for this device. - If devX is the last device for this OPP table, then we don't migrate and just release all resources. - Otherwise, we migrate it to the next element in the list. i.e. any device which != devX.
Please tell based on this where do you see a possibility of a bug. Surely there can be one, but I fail to see it at the moment and need more detail of the same.
Thanks Xiaomeng.
On Mon, 28 Mar 2022 15:09:33 +0530, Viresh Kumar wrote:
On 28-03-22, 17:13, Xiaomeng Tong wrote:
On Mon, 28 Mar 2022 14:20:57 +0530, Viresh Kumar wrote:
On 28-03-22, 15:43, Xiaomeng Tong wrote:
No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: if (!list_is_singular(&opp_table->dev_list)),
while list_is_singlular is: !list_empty(head) && (head->next == head->prev);
so the condition is: list_empty(head) || (head->next != head->prev)
if the list is empty, the bug can be triggered.
List can't be empty here by design. It will be a huge bug in that case, which should lead to crash somewhere.
There is anther condition to trigger this bug: the list is not empty and no element found (if (iter != opp_dev)).
I suggest reading the code again, considering opp_debug_unregister() as well.
What's happening here is this:
- Several devices share the OPP table.
- One of them (devX) is going away and opp_debug_unregister() is called for this device.
- If devX is the last device for this OPP table, then we don't migrate and just release all resources.
- Otherwise, we migrate it to the next element in the list. i.e. any device which != devX.
Please tell based on this where do you see a possibility of a bug. Surely there can be one, but I fail to see it at the moment and need more detail of the same.
Perhaps you are right. Anyway, It is a good choise to use list iterator only inside the loop as linus suggested [1], to avoid potential risk. I have also repost another patch with changed commit message. Please check it, thank you.
[1]:https://lore.kernel.org/lkml/20220301075839.4156-1-xiam0nd.tong@gmail.com/
-- Xiaomeng Tong
linux-stable-mirror@lists.linaro.org
-
Viresh Kumar -
Xiaomeng Tong