[PATCH] md/raid5-ppl: check for NULL ppl_conf in ppl_write_stripe_run()

Syzbot reported a general protection fault
due to a NULL pointer dereference in ppl_write_stripe_run().

When a RAID 5 array operates without Partial Parity Log (PPL) enabled or
before its initialization, conf->log_private remains NULL.
ppl_write_stripe_run() assigns ppl_conf = conf->log_private and
immediately attempts to access ppl_conf->count in the loop header.
This triggers a NULL pointer dereference.

Fix this by returning early
from ppl_write_stripe_run() if ppl_conf is NULL.

Tested-by: syzbot+75d7e96ad03ac2dbbd9f@syzkaller.appspotmail.com
Reported-by: syzbot+75d7e96ad03ac2dbbd9f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=75d7e96ad03ac2dbbd9f
Fixes: 3418d036c81d ("raid5-ppl: Partial Parity Log write logging implementation")
Signed-off-by: Svyatoslav Nikolenko <redacted>
---
 drivers/md/raid5-ppl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/raid5-ppl.c b/drivers/md/raid5-ppl.c
index 7f8a9d3fd578..e54ed4e44b0f 100644
--- a/drivers/md/raid5-ppl.c
+++ b/drivers/md/raid5-ppl.c

@@ -535,6 +535,9 @@ void ppl_write_stripe_run(struct r5conf *conf)
 	struct ppl_log *log;
 	int i;
 
+	if (!ppl_conf)
+		return;
+
 	for (i = 0; i < ppl_conf->count; i++) {
 		log = &ppl_conf->child_logs[i];
 

-- 
2.47.3