linux-kernel - [PATCH] rpadlpar: fix potential drc_name corruption in store functions

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Message-Id: <20210310223021.423155-1-tyreld@linux.ibm.com>
Date:   Wed, 10 Mar 2021 16:30:21 -0600
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     bhelgaas@...gle.com
Cc:     linux-pci@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, mmc@...ux.ibm.com,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Subject: [PATCH] rpadlpar: fix potential drc_name corruption in store functions

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 <tyreld@...ux.ibm.com>
---
 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