[PATCH v2] rpadlpar: fix potential drc_name corruption in store functions

[PATCH v2] rpadlpar: fix potential drc_name corruption in store functions

[Tyrel Datwyler]

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 using strscpy() instead of memcpy() to ensure the string is
NULL terminated when copied into the static drc_name buffer. Further,
since the string is now NULL terminated the code only needs to change
'\n' to '\0' when present.

Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
---

Changes in v2:
* use strscpy instead of memcpy (suggested by mpe)

 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..dbfa0b55d31a 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);
+	strscpy(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);
+	strscpy(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

Re: [PATCH v2] rpadlpar: fix potential drc_name corruption in store functions

[Michael Ellerman]

On Mon, 15 Mar 2021 15:48:21 -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.
> 
> [...]

Applied to powerpc/fixes.

[1/1] rpadlpar: fix potential drc_name corruption in store functions
      https://git.kernel.org/powerpc/c/cc7a0bb058b85ea03db87169c60c7cfdd5d34678

cheers