[Stable-11.1.1 18/42] pc-bios/s390-ccw: fix out-of-bounds read in iso_get_file_size()

From: Joshua Daley <[email protected]>

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")
Cc: [email protected]
Signed-off-by: Joshua Daley <[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Reviewed-by: Matthew Rosato <[email protected]>
Reviewed-by: Eric Farman <[email protected]>
Link: https://lore.kernel.org/qemu-devel/[email protected]
[[email protected]: Fixed typo on Christian's tag, added qemu-stable]
Signed-off-by: Eric Farman <[email protected]>
(cherry picked from commit a9f1e84c6b8213fb1bfc664b1ffa1a8d975a69b6)
Signed-off-by: Michael Tokarev <[email protected]>

diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
index 420ee32eff8..ed6e8cbbc78 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;
             }
-- 
2.47.3