Both add_slot_store() and remove_slot_store() try to fix up the drc_name
copied from the store buffer by placing a NULL terminator at nbyte + 1
or in place of a '\n' if present. However, the static buffer that we
copy the drc_name data into is not zeored and can contain anything past
the n-th byte. This is problematic if a '\n' byte appears in that buffer
after nbytes and the string copied into the store buffer was not NULL
terminated to start with as the strchr() search for a '\n' byte will mark
this incorrectly as the end of the drc_name string resulting in a drc_name
string that contains garbage data after the n-th byte. The following
debugging shows an example of the drmgr utility writing "PHB 4543" to
the add_slot sysfs attribute, but add_slot_store logging a corrupted
string value.
[135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1
[135823.702879] add_slot_store: drc_name = PHB 4543°|<82>!, rc = -19
Fix this by NULL terminating the string when we copy it into our static
buffer by coping nbytes + 1 of data from the store buffer. The code has
already made sure that nbytes is not >= MAX_DRC_NAME_LEN and the store
buffer is guaranteed to be zeroed beyond the nth-byte of data copied
from the user. Further, since the string is now NULL terminated the code
only needs to change '\n' to '\0' when present.
Signed-off-by: Tyrel Datwyler <[email protected]>
---
drivers/pci/hotplug/rpadlpar_sysfs.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c
index cdbfa5df3a51..375087921284 100644
--- a/drivers/pci/hotplug/rpadlpar_sysfs.c
+++ b/drivers/pci/hotplug/rpadlpar_sysfs.c
@@ -34,12 +34,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr,
if (nbytes >= MAX_DRC_NAME_LEN)
return 0;
- memcpy(drc_name, buf, nbytes);
+ memcpy(drc_name, buf, nbytes + 1);
end = strchr(drc_name, '\n');
- if (!end)
- end = &drc_name[nbytes];
- *end = '\0';
+ if (end)
+ *end = '\0';
rc = dlpar_add_slot(drc_name);
if (rc)
@@ -65,12 +64,11 @@ static ssize_t remove_slot_store(struct kobject *kobj,
if (nbytes >= MAX_DRC_NAME_LEN)
return 0;
- memcpy(drc_name, buf, nbytes);
+ memcpy(drc_name, buf, nbytes + 1);
end = strchr(drc_name, '\n');
- if (!end)
- end = &drc_name[nbytes];
- *end = '\0';
+ if (end)
+ *end = '\0';
rc = dlpar_remove_slot(drc_name);
if (rc)
--
2.27.0
On Wed, Mar 10, 2021 at 04:30:21PM -0600, Tyrel Datwyler wrote:
> Both add_slot_store() and remove_slot_store() try to fix up the drc_name
> copied from the store buffer by placing a NULL terminator at nbyte + 1
> or in place of a '\n' if present. However, the static buffer that we
> copy the drc_name data into is not zeored and can contain anything past
> the n-th byte. This is problematic if a '\n' byte appears in that buffer
> after nbytes and the string copied into the store buffer was not NULL
> terminated to start with as the strchr() search for a '\n' byte will mark
> this incorrectly as the end of the drc_name string resulting in a drc_name
> string that contains garbage data after the n-th byte. The following
> debugging shows an example of the drmgr utility writing "PHB 4543" to
> the add_slot sysfs attribute, but add_slot_store logging a corrupted
> string value.
>
> [135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1
> [135823.702879] add_slot_store: drc_name = PHB 4543?|<82>!, rc = -19
>
> Fix this by NULL terminating the string when we copy it into our static
> buffer by coping nbytes + 1 of data from the store buffer. The code has
Why is it OK to copy nbytes + 1 and why is it expected that the buffer
contains a nul after the content?
Isn't it much saner to just nul terminate the string after copying?
diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c
index cdbfa5df3a51..cfbad67447da 100644
--- a/drivers/pci/hotplug/rpadlpar_sysfs.c
+++ b/drivers/pci/hotplug/rpadlpar_sysfs.c
@@ -35,11 +35,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr,
return 0;
memcpy(drc_name, buf, nbytes);
+ &drc_name[nbytes] = '\0';
end = strchr(drc_name, '\n');
- if (!end)
- end = &drc_name[nbytes];
- *end = '\0';
+ if (end)
+ *end = '\0';
rc = dlpar_add_slot(drc_name);
if (rc)
@@ -66,11 +66,11 @@ static ssize_t remove_slot_store(struct kobject *kobj,
return 0;
memcpy(drc_name, buf, nbytes);
+ &drc_name[nbytes] = '\0';
end = strchr(drc_name, '\n');
- if (!end)
- end = &drc_name[nbytes];
- *end = '\0';
+ if (end)
+ *end = '\0';
rc = dlpar_remove_slot(drc_name);
if (rc)
Thanks
Michal
> already made sure that nbytes is not >= MAX_DRC_NAME_LEN and the store
> buffer is guaranteed to be zeroed beyond the nth-byte of data copied
> from the user. Further, since the string is now NULL terminated the code
> only needs to change '\n' to '\0' when present.
>
> Signed-off-by: Tyrel Datwyler <[email protected]>
> ---
> drivers/pci/hotplug/rpadlpar_sysfs.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c
> index cdbfa5df3a51..375087921284 100644
> --- a/drivers/pci/hotplug/rpadlpar_sysfs.c
> +++ b/drivers/pci/hotplug/rpadlpar_sysfs.c
> @@ -34,12 +34,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr,
> if (nbytes >= MAX_DRC_NAME_LEN)
> return 0;
>
> - memcpy(drc_name, buf, nbytes);
> + memcpy(drc_name, buf, nbytes + 1);
>
> end = strchr(drc_name, '\n');
> - if (!end)
> - end = &drc_name[nbytes];
> - *end = '\0';
> + if (end)
> + *end = '\0';
>
> rc = dlpar_add_slot(drc_name);
> if (rc)
> @@ -65,12 +64,11 @@ static ssize_t remove_slot_store(struct kobject *kobj,
> if (nbytes >= MAX_DRC_NAME_LEN)
> return 0;
>
> - memcpy(drc_name, buf, nbytes);
> + memcpy(drc_name, buf, nbytes + 1);
>
> end = strchr(drc_name, '\n');
> - if (!end)
> - end = &drc_name[nbytes];
> - *end = '\0';
> + if (end)
> + *end = '\0';
>
> rc = dlpar_remove_slot(drc_name);
> if (rc)
> --
> 2.27.0
>
On 3/13/21 1:17 AM, Michal Suchánek wrote:
> On Wed, Mar 10, 2021 at 04:30:21PM -0600, Tyrel Datwyler wrote:
>> Both add_slot_store() and remove_slot_store() try to fix up the drc_name
>> copied from the store buffer by placing a NULL terminator at nbyte + 1
>> or in place of a '\n' if present. However, the static buffer that we
>> copy the drc_name data into is not zeored and can contain anything past
>> the n-th byte. This is problematic if a '\n' byte appears in that buffer
>> after nbytes and the string copied into the store buffer was not NULL
>> terminated to start with as the strchr() search for a '\n' byte will mark
>> this incorrectly as the end of the drc_name string resulting in a drc_name
>> string that contains garbage data after the n-th byte. The following
>> debugging shows an example of the drmgr utility writing "PHB 4543" to
>> the add_slot sysfs attribute, but add_slot_store logging a corrupted
>> string value.
>>
>> [135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1
>> [135823.702879] add_slot_store: drc_name = PHB 4543°|<82>!, rc = -19
>>
>> Fix this by NULL terminating the string when we copy it into our static
>> buffer by coping nbytes + 1 of data from the store buffer. The code has
> Why is it OK to copy nbytes + 1 and why is it expected that the buffer
> contains a nul after the content?
It is my understanding that the store function buffer is allocated as a
zeroed-page which the kernel copies up to at most (PAGE_SIZE - 1) of user data
into. Anything after nbytes would therefore be zeroed.
>
> Isn't it much saner to just nul terminate the string after copying?
At the cost of an extra line of code, sure.
-Tyrel
>
> diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c
> index cdbfa5df3a51..cfbad67447da 100644
> --- a/drivers/pci/hotplug/rpadlpar_sysfs.c
> +++ b/drivers/pci/hotplug/rpadlpar_sysfs.c
> @@ -35,11 +35,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr,
> return 0;
>
> memcpy(drc_name, buf, nbytes);
> + &drc_name[nbytes] = '\0';
>
> end = strchr(drc_name, '\n');
> - if (!end)
> - end = &drc_name[nbytes];
> - *end = '\0';
> + if (end)
> + *end = '\0';
>
> rc = dlpar_add_slot(drc_name);
> if (rc)
> @@ -66,11 +66,11 @@ static ssize_t remove_slot_store(struct kobject *kobj,
> return 0;
>
> memcpy(drc_name, buf, nbytes);
> + &drc_name[nbytes] = '\0';
>
> end = strchr(drc_name, '\n');
> - if (!end)
> - end = &drc_name[nbytes];
> - *end = '\0';
> + if (end)
> + *end = '\0';
>
> rc = dlpar_remove_slot(drc_name);
> if (rc)
>
> Thanks
>
> Michal
>
>> already made sure that nbytes is not >= MAX_DRC_NAME_LEN and the store
>> buffer is guaranteed to be zeroed beyond the nth-byte of data copied
>> from the user. Further, since the string is now NULL terminated the code
>> only needs to change '\n' to '\0' when present.
>>
>> Signed-off-by: Tyrel Datwyler <[email protected]>
>> ---
>> drivers/pci/hotplug/rpadlpar_sysfs.c | 14 ++++++--------
>> 1 file changed, 6 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/hotplug/rpadlpar_sysfs.c b/drivers/pci/hotplug/rpadlpar_sysfs.c
>> index cdbfa5df3a51..375087921284 100644
>> --- a/drivers/pci/hotplug/rpadlpar_sysfs.c
>> +++ b/drivers/pci/hotplug/rpadlpar_sysfs.c
>> @@ -34,12 +34,11 @@ static ssize_t add_slot_store(struct kobject *kobj, struct kobj_attribute *attr,
>> if (nbytes >= MAX_DRC_NAME_LEN)
>> return 0;
>>
>> - memcpy(drc_name, buf, nbytes);
>> + memcpy(drc_name, buf, nbytes + 1);
>>
>> end = strchr(drc_name, '\n');
>> - if (!end)
>> - end = &drc_name[nbytes];
>> - *end = '\0';
>> + if (end)
>> + *end = '\0';
>>
>> rc = dlpar_add_slot(drc_name);
>> if (rc)
>> @@ -65,12 +64,11 @@ static ssize_t remove_slot_store(struct kobject *kobj,
>> if (nbytes >= MAX_DRC_NAME_LEN)
>> return 0;
>>
>> - memcpy(drc_name, buf, nbytes);
>> + memcpy(drc_name, buf, nbytes + 1);
>>
>> end = strchr(drc_name, '\n');
>> - if (!end)
>> - end = &drc_name[nbytes];
>> - *end = '\0';
>> + if (end)
>> + *end = '\0';
>>
>> rc = dlpar_remove_slot(drc_name);
>> if (rc)
>> --
>> 2.27.0
>>
Tyrel Datwyler <[email protected]> writes:
> On 3/13/21 1:17 AM, Michal Suchánek wrote:
>> On Wed, Mar 10, 2021 at 04:30:21PM -0600, Tyrel Datwyler wrote:
>>> Both add_slot_store() and remove_slot_store() try to fix up the drc_name
>>> copied from the store buffer by placing a NULL terminator at nbyte + 1
>>> or in place of a '\n' if present. However, the static buffer that we
>>> copy the drc_name data into is not zeored and can contain anything past
>>> the n-th byte. This is problematic if a '\n' byte appears in that buffer
>>> after nbytes and the string copied into the store buffer was not NULL
>>> terminated to start with as the strchr() search for a '\n' byte will mark
>>> this incorrectly as the end of the drc_name string resulting in a drc_name
>>> string that contains garbage data after the n-th byte. The following
>>> debugging shows an example of the drmgr utility writing "PHB 4543" to
>>> the add_slot sysfs attribute, but add_slot_store logging a corrupted
>>> string value.
>>>
>>> [135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1
>>> [135823.702879] add_slot_store: drc_name = PHB 4543°|<82>!, rc = -19
>>>
>>> Fix this by NULL terminating the string when we copy it into our static
>>> buffer by coping nbytes + 1 of data from the store buffer. The code has
>> Why is it OK to copy nbytes + 1 and why is it expected that the buffer
>> contains a nul after the content?
>
> It is my understanding that the store function buffer is allocated as a
> zeroed-page which the kernel copies up to at most (PAGE_SIZE - 1) of user data
> into. Anything after nbytes would therefore be zeroed.
I think that's true, but it would be nice if we didn't have to rely on
that obscure detail in order for this code to be correct & understandable.
>> Isn't it much saner to just nul terminate the string after copying?
>
> At the cost of an extra line of code, sure.
Is there a reason we can't use strscpy()? That should deal with all the
corner cases around the string copy, and then all you have to do is look
for a newline and turn it into nul.
cheers
On 3/14/21 7:52 PM, Michael Ellerman wrote:
> Tyrel Datwyler <[email protected]> writes:
>> On 3/13/21 1:17 AM, Michal Suchánek wrote:
>>> On Wed, Mar 10, 2021 at 04:30:21PM -0600, Tyrel Datwyler wrote:
>>>> Both add_slot_store() and remove_slot_store() try to fix up the drc_name
>>>> copied from the store buffer by placing a NULL terminator at nbyte + 1
>>>> or in place of a '\n' if present. However, the static buffer that we
>>>> copy the drc_name data into is not zeored and can contain anything past
>>>> the n-th byte. This is problematic if a '\n' byte appears in that buffer
>>>> after nbytes and the string copied into the store buffer was not NULL
>>>> terminated to start with as the strchr() search for a '\n' byte will mark
>>>> this incorrectly as the end of the drc_name string resulting in a drc_name
>>>> string that contains garbage data after the n-th byte. The following
>>>> debugging shows an example of the drmgr utility writing "PHB 4543" to
>>>> the add_slot sysfs attribute, but add_slot_store logging a corrupted
>>>> string value.
>>>>
>>>> [135823.702864] drmgr: drmgr: -c phb -a -s PHB 4543 -d 1
>>>> [135823.702879] add_slot_store: drc_name = PHB 4543°|<82>!, rc = -19
>>>>
>>>> Fix this by NULL terminating the string when we copy it into our static
>>>> buffer by coping nbytes + 1 of data from the store buffer. The code has
>>> Why is it OK to copy nbytes + 1 and why is it expected that the buffer
>>> contains a nul after the content?
>>
>> It is my understanding that the store function buffer is allocated as a
>> zeroed-page which the kernel copies up to at most (PAGE_SIZE - 1) of user data
>> into. Anything after nbytes would therefore be zeroed.
>
> I think that's true, but it would be nice if we didn't have to rely on
> that obscure detail in order for this code to be correct & understandable.
I think its a security guarantee, but I guess barring a comment that explicitly
outlines the correctness it probably isn't obvious.
>
>>> Isn't it much saner to just nul terminate the string after copying?
>>
>> At the cost of an extra line of code, sure.
>
> Is there a reason we can't use strscpy()? That should deal with all the
> corner cases around the string copy, and then all you have to do is look
> for a newline and turn it into nul.
Fine with me. I'll spin v2 with strscpy().
-Tyrel
>
> cheers
>