Hi,
Static analysis on linux-next with Coverity has detected an issue in
drivers/misc/cardreader/alcor_pci.c in function
alcor_pci_init_check_aspm with the following commit:
commit 3ce3e45cc333da707d4d6eb433574b990bcc26f5
Author: Tong Zhang <[email protected]>
Date: Thu May 13 00:07:33 2021 -0400
misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge
The analysis is as follows:
135 static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
136 {
137 struct pci_dev *pci;
138 int where;
139 u32 val32;
140
141 priv->pdev_cap_off = alcor_pci_find_cap_offset(priv,
priv->pdev);
142 /*
143 * A device might be attached to root complex directly and
144 * priv->parent_pdev will be NULL. In this case we don't
check its
145 * capability and disable ASPM completely.
146 */
1. Condition !priv->parent_pdev, taking true branch.
2. var_compare_op: Comparing priv->parent_pdev to null implies that
priv->parent_pdev might be null.
147 if (!priv->parent_pdev)
Dereference after null check (FORWARD_NULL)
3. var_deref_model: Passing null pointer priv->parent_pdev to
alcor_pci_find_cap_offset, which dereferences it.
148 priv->parent_cap_off = alcor_pci_find_cap_offset(priv,
149
priv->parent_pdev);
When !priv->parent_pdev is true, then priv->parent_pdev is NULL and
hence the call to alcor_pci_find_cap_offset() is dereferencing a null
pointer in the priv->parent_pdev argument.
I suspect the logic in the if statement is inverted, the ! should be
removed. This seems too trivial to be wrong. Maybe I'm missing something
deeper.
Colin
On Tue, May 18, 2021 at 11:32 AM Colin Ian King
<[email protected]> wrote:
>
> Hi,
>
> Static analysis on linux-next with Coverity has detected an issue in
> drivers/misc/cardreader/alcor_pci.c in function
> alcor_pci_init_check_aspm with the following commit:
>
> commit 3ce3e45cc333da707d4d6eb433574b990bcc26f5
> Author: Tong Zhang <[email protected]>
> Date: Thu May 13 00:07:33 2021 -0400
>
> misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge
>
> The analysis is as follows:
>
> 135 static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
> 136 {
> 137 struct pci_dev *pci;
> 138 int where;
> 139 u32 val32;
> 140
> 141 priv->pdev_cap_off = alcor_pci_find_cap_offset(priv,
> priv->pdev);
> 142 /*
> 143 * A device might be attached to root complex directly and
> 144 * priv->parent_pdev will be NULL. In this case we don't
> check its
> 145 * capability and disable ASPM completely.
> 146 */
>
> 1. Condition !priv->parent_pdev, taking true branch.
> 2. var_compare_op: Comparing priv->parent_pdev to null implies that
> priv->parent_pdev might be null.
>
> 147 if (!priv->parent_pdev)
>
> Dereference after null check (FORWARD_NULL)
> 3. var_deref_model: Passing null pointer priv->parent_pdev to
> alcor_pci_find_cap_offset, which dereferences it.
>
> 148 priv->parent_cap_off = alcor_pci_find_cap_offset(priv,
> 149
> priv->parent_pdev);
>
> When !priv->parent_pdev is true, then priv->parent_pdev is NULL and
> hence the call to alcor_pci_find_cap_offset() is dereferencing a null
> pointer in the priv->parent_pdev argument.
>
> I suspect the logic in the if statement is inverted, the ! should be
> removed. This seems too trivial to be wrong. Maybe I'm missing something
> deeper.
Hi Colin,
Thanks for pointing that out.
You are right. I made a terrible mistake here while refactoring the patch. :'(
I think I need to get away from this thing for a while and have some rest.
- Tong
>
> Colin
>
There is an issue with the ASPM(optional) capability checking function.
A device might be attached to root complex directly, in this case,
bus->self(bridge) will be NULL, thus priv->parent_pdev is NULL.
Since alcor_pci_init_check_aspm(priv->parent_pdev) checks the PCI link's
ASPM capability and populate parent_cap_off, which will be used later by
alcor_pci_aspm_ctrl() to dynamically turn on/off device, what we can do
here is to avoid checking the capability if we are on the root complex.
This will make pdev_cap_off 0 and alcor_pci_aspm_ctrl() will simply
return when bring called, effectively disable ASPM for the device.
[ 1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0
[ 1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40
[ 1.253998] Call Trace:
[ 1.254131] ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci]
[ 1.254476] alcor_pci_probe+0x169/0x2d5 [alcor_pci]
Signed-off-by: Tong Zhang <[email protected]>
Co-developed-by: Greg Kroah-Hartman <[email protected]>
Co-developed-by: Colin Ian King <[email protected]>
---
v2: check before calling alcor_pci_find_cap_offset()
v3: Add comment. Enable the dev_dbg() output when priv->parent_pdev is NULL.
v4: fix inverted if statement, thanks to Colin <[email protected]>
drivers/misc/cardreader/alcor_pci.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/cardreader/alcor_pci.c b/drivers/misc/cardreader/alcor_pci.c
index cd402c89189e..de6d44a158bb 100644
--- a/drivers/misc/cardreader/alcor_pci.c
+++ b/drivers/misc/cardreader/alcor_pci.c
@@ -139,7 +139,13 @@ static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
u32 val32;
priv->pdev_cap_off = alcor_pci_find_cap_offset(priv, priv->pdev);
- priv->parent_cap_off = alcor_pci_find_cap_offset(priv,
+ /*
+ * A device might be attached to root complex directly and
+ * priv->parent_pdev will be NULL. In this case we don't check its
+ * capability and disable ASPM completely.
+ */
+ if (priv->parent_pdev)
+ priv->parent_cap_off = alcor_pci_find_cap_offset(priv,
priv->parent_pdev);
if ((priv->pdev_cap_off == 0) || (priv->parent_cap_off == 0)) {
--
2.25.1
On Tue, May 18, 2021 at 03:28:18PM -0400, Tong Zhang wrote:
> There is an issue with the ASPM(optional) capability checking function.
> A device might be attached to root complex directly, in this case,
> bus->self(bridge) will be NULL, thus priv->parent_pdev is NULL.
> Since alcor_pci_init_check_aspm(priv->parent_pdev) checks the PCI link's
> ASPM capability and populate parent_cap_off, which will be used later by
> alcor_pci_aspm_ctrl() to dynamically turn on/off device, what we can do
> here is to avoid checking the capability if we are on the root complex.
> This will make pdev_cap_off 0 and alcor_pci_aspm_ctrl() will simply
> return when bring called, effectively disable ASPM for the device.
>
> [ 1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0
> [ 1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40
> [ 1.253998] Call Trace:
> [ 1.254131] ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci]
> [ 1.254476] alcor_pci_probe+0x169/0x2d5 [alcor_pci]
>
> Signed-off-by: Tong Zhang <[email protected]>
> Co-developed-by: Greg Kroah-Hartman <[email protected]>
> Co-developed-by: Colin Ian King <[email protected]>
> ---
> v2: check before calling alcor_pci_find_cap_offset()
> v3: Add comment. Enable the dev_dbg() output when priv->parent_pdev is NULL.
> v4: fix inverted if statement, thanks to Colin <[email protected]>
Please just send a fix-up patch instead, I don't want to revert and then
add this, that doesn't make any sense...
thanks,
greg k-h
On Fri, May 21, 2021 at 5:44 AM Greg Kroah-Hartman
<[email protected]> wrote:
> Please just send a fix-up patch instead, I don't want to revert and then
> add this, that doesn't make any sense...
>
> thanks,
>
> greg k-h
OK,OK, got it. Thanks for letting me know how to fix this.
I will send out a fix-up patch as suggested ASAP.
Thanks,
- Tong
This patch fixes a trivial mistake that I made in the previous attempt
in fixing the null bridge issue. The branch condition is inverted and we
should call alcor_pci_find_cap_offset() only if bridge is not null.
Reported-by: Colin Ian King <[email protected]>
Fixes: 3ce3e45cc333 ("misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge")
Signed-off-by: Tong Zhang <[email protected]>
---
drivers/misc/cardreader/alcor_pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/misc/cardreader/alcor_pci.c b/drivers/misc/cardreader/alcor_pci.c
index 0a62307f7ffb..de6d44a158bb 100644
--- a/drivers/misc/cardreader/alcor_pci.c
+++ b/drivers/misc/cardreader/alcor_pci.c
@@ -144,7 +144,7 @@ static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
* priv->parent_pdev will be NULL. In this case we don't check its
* capability and disable ASPM completely.
*/
- if (!priv->parent_pdev)
+ if (priv->parent_pdev)
priv->parent_cap_off = alcor_pci_find_cap_offset(priv,
priv->parent_pdev);
--
2.25.1
Hi Greg,
I have sent out a fix-up patch as suggested.
Please take a look to see if this one works.
Sorry for the trouble. and have a nice weekend.
- Tong