[PATCH] cred - synchronize rcu before releasing cred
in [Kernel]
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From: Jiri Olsa on 16 Jun 2010 08:30 hi, BZ 591015 - kernel BUG at kernel/cred.c:168 https://bugzilla.redhat.com/show_bug.cgi?id=591015 Above bugzilla reported bug during the releasing of old cred structure. There is reproducer attached to the bugzilla. The issue is caused by releasing old cred struct while other kernel path might be still using it. This leads to cred->usage inconsistency inside the __put_cred and triggering the bug. Following kernel paths are affected: The CPU1 path is setting the new groups creds. The CPU2 path is cat /proc/PID/status CPU 1 CPU 2 sys_setgroups proc_pid_status set_current_groups task_state commit_creds rcu_read_lock put_cred ... __put_cred get_cred BUG_ON(usage != 0) ... rcu_read_unlock If __put_cred got executed during the CPU2 holding the reference the BUG_ON inside __put_cred is trigered. I put synchronize_rcu before put_cred call, so we are sure all the rcu_read_lock blocks are finished, and if needed, using new creds. Also I moved rcu_read_unlock below the put_cred for consistency. wbr, jirka Signed-off-by: Jiri Olsa <jolsa(a)redhat.com> --- fs/proc/array.c | 3 ++- kernel/cred.c | 6 ++++++ 2 files changed, 8 insertions(+), 1 deletions(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 9b58d38..c0e60d1 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -199,7 +199,6 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, "FDSize:\t%d\n" "Groups:\t", fdt ? fdt->max_fds : 0); - rcu_read_unlock(); group_info = cred->group_info; task_unlock(p); @@ -208,6 +207,8 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, seq_printf(m, "%d ", GROUP_AT(group_info, g)); put_cred(cred); + rcu_read_unlock(); + seq_printf(m, "\n"); } diff --git a/kernel/cred.c b/kernel/cred.c index a2d5504..4872f12 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -510,6 +510,12 @@ int commit_creds(struct cred *new) new->fsgid != old->fsgid) proc_id_connector(task, PROC_EVENT_GID); + /* + * New cred is set already, now let the old one + * chance to disappear on other CPUs. + */ + synchronize_rcu(); + /* release the old obj and subj refs both */ put_cred(old); put_cred(old); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |