From: David Howells <[email protected]>
=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================
commit 694f690d27dadccc8cb9d90532e76593b61fe098 upstream.
Commit 8f92054e7ca1 ("CRED: Fix __task_cred()'s lockdep check and banner
comment") fixed the lockdep checks on __task_cred(). This has shown up
a place in the signalling code where a lock should be held - namely that
check_kill_permission() requires its callers to hold the RCU lock.
Fix group_send_sig_info() to get the RCU read lock around its call to
check_kill_permission().
Without this patch, the following warning can occur:
===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
kernel/signal.c:660 invoked rcu_dereference_check() without protection!
...
Reported-by: Tetsuo Handa <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Paul Gortmaker <[email protected]>
---
kernel/signal.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 48f2130..edabc2f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -637,7 +637,7 @@ static inline bool si_fromuser(const struct siginfo *info)
/*
* Bad permissions for sending the signal
- * - the caller must hold at least the RCU read lock
+ * - the caller must hold the RCU read lock
*/
static int check_kill_permission(int sig, struct siginfo *info,
struct task_struct *t)
@@ -1126,11 +1126,14 @@ struct sighand_struct *lock_task_sighand(struct
task_struct *tsk, unsigned long
/*
* send signal info to all the members of a group
- * - the caller must hold the RCU read lock at least
*/
int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
- int ret = check_kill_permission(sig, info, p);
+ int ret;
+
+ rcu_read_lock();
+ ret = check_kill_permission(sig, info, p);
+ rcu_read_unlock();
if (!ret && sig)
ret = do_send_sig_info(sig, info, p, true);
--
1.7.4.4
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