[PATCH 3/5] pc-bios/s390-ccw: fix out-of-bounds read in iso_get_file_size()

[Christian Borntraeger <borntraeger@linux.ibm.com>]

From: Joshua Daley <jdaley@linux.ibm.com>

In the dir_rem[level] == 0 case, level is decremented, then
a virtio_read() is issued on sec_loc[level]. If level is -1, then the
4 bytes before the static sec_loc array are read, and the virtio_read()
is issued on that garbage block number.

Guard the call to virtio_read() against the value of level to prevent
this.

Fixes: 869648e87eeb ("pc-bios/s390-ccw: El Torito 16-bit boot image size field workaround")
Signed-off-by: Joshua Daley <jdaley@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@inux.ibm.com>
---
 pc-bios/s390-ccw/bootmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
index 420ee32eff..ed6e8cbbc7 100644
--- a/pc-bios/s390-ccw/bootmap.c
+++ b/pc-bios/s390-ccw/bootmap.c
@@ -902,7 +902,7 @@ static inline long iso_get_file_size(uint32_t load_rba)
         if (dir_rem[level] == 0) {
             /* Nothing remaining */
             level--;
-            if (virtio_read(sec_loc[level], temp)) {
+            if (level >= 0 && virtio_read(sec_loc[level], temp)) {
                 puts("Failed to read ISO directory");
                 return -EIO;
             }
-- 
2.53.0