[PATCH] io_uring/rsrc: fix null ptr dereference in io_sqe_buffer_register

[Daniel Yang]

The call stack io_sqe_buffer_register -> io_buffer_account_pin ->
headpage_already_acct results in a null ptr dereference in the for loop.
There is no guarantee that ctx->buf_table.nodes[i] is an allocated node
so add a check if null before dereferencing.

Signed-off-by: Daniel Yang <danielyangkang@xxxxxxxxx>
Reported-by: syzbot+05c0f12a4d43d656817e@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=05c0f12a4d43d656817e
Fixes: 661768085e99 ("io_uring/rsrc: get rid of the empty node and dummy_ubuf")
---
 io_uring/rsrc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index af60d9f59..e2edb752a 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -581,6 +581,8 @@ static bool headpage_already_acct(struct io_ring_ctx *ctx, struct page **pages,
 	/* check previously registered pages */
 	for (i = 0; i < ctx->buf_table.nr; i++) {
 		struct io_rsrc_node *node = ctx->buf_table.nodes[i];
+		if (!node)
+			continue;
 		struct io_mapped_ubuf *imu = node->buf;
 
 		for (j = 0; j < imu->nr_bvecs; j++) {
-- 
2.39.2