[SRU][Jammy][PATCH 1/1] io_uring/fdinfo: lock SQ thread while retrieving thread cpu/pid

[Bethany Jamison]

From: Jens Axboe <axboe at kernel.dk>

We could race with SQ thread exit, and if we do, we'll hit a NULL pointer
dereference when the thread is cleared. Grab the SQPOLL data lock before
attempting to get the task cpu and pid for fdinfo, this ensures we have a
stable view of it.

Cc: stable at vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218032
Reviewed-by: Gabriel Krisman Bertazi <krisman at suse.de>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(manually backported from commit 7644b1a1c9a7ae8ab99175989bfc8676055edb46)
[bjamison: io_uring in Jammy is structured very differently than upstream,
applied all changes from 764 to relevant section of code]
CVE-2023-46862
Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
---
 io_uring/io_uring.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 18f10776cc4df..a1ba99e242e31 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -10436,7 +10436,7 @@ static int io_uring_show_cred(struct seq_file *m, unsigned int id,
 
 static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 {
-	struct io_sq_data *sq = NULL;
+	int sq_pid = -1, sq_cpu = -1;
 	bool has_lock;
 	int i;
 
@@ -10449,13 +10449,19 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 	has_lock = mutex_trylock(&ctx->uring_lock);
 
 	if (has_lock && (ctx->flags & IORING_SETUP_SQPOLL)) {
-		sq = ctx->sq_data;
-		if (!sq->thread)
-			sq = NULL;
+		struct io_sq_data *sq = ctx->sq_data;
+
+		if (mutex_trylock(&sq->lock)) {
+			if (sq->thread) {
+				sq_pid = task_pid_nr(sq->thread);
+				sq_cpu = task_cpu(sq->thread);
+			}
+			mutex_unlock(&sq->lock);
+		}
 	}
 
-	seq_printf(m, "SqThread:\t%d\n", sq ? task_pid_nr(sq->thread) : -1);
-	seq_printf(m, "SqThreadCpu:\t%d\n", sq ? task_cpu(sq->thread) : -1);
+	seq_printf(m, "SqThread:\t%d\n", sq_pid);
+	seq_printf(m, "SqThreadCpu:\t%d\n", sq_cpu);
 	seq_printf(m, "UserFiles:\t%u\n", ctx->nr_user_files);
 	for (i = 0; has_lock && i < ctx->nr_user_files; i++) {
 		struct file *f = io_file_from_index(ctx, i);
-- 
2.34.1