The ima_measurements list is append-only and doesn't require
rcu_read_lock() protection. However, lockdep issues a warning when
traversing RCU lists without the read lock:
security/integrity/ima/ima_kexec.c:40 RCU-list traversed in non-reader section!!
Fix this by using the variant of list_for_each_entry_rcu() with the last
argument set to true. This tells the RCU subsystem that traversing this
append-only list without the read lock is intentional and safe.
This change silences the lockdep warning while maintaining the correct
semantics for the append-only list traversal.
Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v2:
- Do not hold the RCU read lock, but, annotate list_for_each_entry_rcu()
that is OK to traverse the list without the RCU read lock.
- Link to v1: https://lore.kernel.org/r/20241104-ima_rcu-v1-1-5157460c5907@debian.org
---
security/integrity/ima/ima_kexec.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 52e00332defed39774c9e23e045f1377cfa30d0c..9d45f4d26f731658a79b94b9f95f4dcc4dcb6325 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -37,7 +37,8 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
memset(&khdr, 0, sizeof(khdr));
khdr.version = 1;
- list_for_each_entry_rcu(qe, &ima_measurements, later) {
+ /* This is an append-only list, no need to hold the RCU read lock */
+ list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
if (file.count < file.size) {
khdr.count++;
ima_measurements_show(&file, qe);
---
base-commit: ac24e26aa08fe026804f678599f805eb13374a5d
change-id: 20241104-ima_rcu-ee83da87d050
Best regards,
--
Breno Leitao <leitao@debian.org>