[PATCH] kdb: prevent possible null deref in kdb_msg_write

Cengiz Can
2020-06-29T19:12:06Z

`kdb_msg_write` operates on a global `struct kgdb_io *` called
`dbg_io_ops`.

Although it is initialized in `debug_core.c`, there's a null check in
`kdb_msg_write` which implies that it can be null whenever we dereference
it in this function call.

Coverity scanner caught this as CID 1465042.

I have modified the function to bail out if `dbg_io_ops` is not properly
initialized.

Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
---
kernel/debug/kdb/kdb_io.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 683a799618ad..85e579812458 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -549,14 +549,15 @@ static void kdb_msg_write(const char *msg, int msg_len)
if (msg_len == 0)
return;

- if (dbg_io_ops) {
- const char *cp = msg;
- int len = msg_len;
+ if (!dbg_io_ops)
+ return;

- while (len--) {
- dbg_io_ops->write_char(*cp);
- cp++;
- }
+ const char *cp = msg;
+ int len = msg_len;
+
+ while (len--) {
+ dbg_io_ops->write_char(*cp);
+ cp++;
}

for_each_console(c) {
--
2.27.0