SCSI: fix new bug in scsi_dev_info_list string matching

Commit b704f70ce200 ("SCSI: fix bug in scsi_dev_info_list matching")
changed the way vendor- and model-string matching was carried out in the
routine that looks up entries in a SCSI devinfo list.  The new matching
code failed to take into account the case of a maximum-length string; in
such cases it could end up testing for a terminating '\0' byte beyond
the end of the memory allocated to the string.  This out-of-bounds bug
was detected by UBSAN.

I don't know if anybody has actually encountered this bug.  The symptom
would be that a device entry in the blacklist might not be matched
properly if it contained an 8-character vendor name or a 16-character
model name.  Such entries certainly exist in scsi_static_device_list.

This patch fixes the problem by adding a check for a maximum-length
string before the '\0' test.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Fixes: b704f70ce200 ("SCSI: fix bug in scsi_dev_info_list matching")
Tested-by: Wilfried Klaebe <linux-kernel@lebenslange-mailadresse.de>
CC: <stable@vger.kernel.org> # v4.4+
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
index ff41c310c900a5760bf33423a5db4362c5dfc25b..eaccd651ccda0d239af91ebfb6dfdbd97ac340e3 100644 (file)
--- a/drivers/scsi/scsi_devinfo.c
+++ b/drivers/scsi/scsi_devinfo.c
@@ -429,7 +429,7 @@ static struct scsi_dev_info_list *scsi_dev_info_list_find(const char *vendor,
         * here, and we don't know what device it is
         * trying to work with, leave it as-is.
         */
-       vmax = 8;       /* max length of vendor */
+       vmax = sizeof(devinfo->vendor);
        vskip = vendor;
        while (vmax > 0 && *vskip == ' ') {
                vmax--;
@@ -439,7 +439,7 @@ static struct scsi_dev_info_list *scsi_dev_info_list_find(const char *vendor,
        while (vmax > 0 && vskip[vmax - 1] == ' ')
                --vmax;
 
-       mmax = 16;      /* max length of model */
+       mmax = sizeof(devinfo->model);
        mskip = model;
        while (mmax > 0 && *mskip == ' ') {
                mmax--;
@@ -455,10 +455,12 @@ static struct scsi_dev_info_list *scsi_dev_info_list_find(const char *vendor,
                         * Behave like the older version of get_device_flags.
                         */
                        if (memcmp(devinfo->vendor, vskip, vmax) ||
-                                       devinfo->vendor[vmax])
+                                       (vmax < sizeof(devinfo->vendor) &&
+                                               devinfo->vendor[vmax]))
                                continue;
                        if (memcmp(devinfo->model, mskip, mmax) ||
-                                       devinfo->model[mmax])
+                                       (mmax < sizeof(devinfo->model) &&
+                                               devinfo->model[mmax]))
                                continue;
                        return devinfo;
                } else {