On Fri, 7 Aug 2026 17:04:08 -0400 Steven Rostedt <[email protected]> wrote:
> From: Steven Rostedt <[email protected]> > > When an eventfs inode is freed, it sets ei->is_freed and then uses its > ei->list to add it to the srcu link list as the list field is a union with > the rcu list head. As the ei->list is used to iterate over an SRCU > protected list without taking the eventfs_mutex, there's nothing stopping > the iteration over that list to see the ei->rcu instead of the ei->list > and it will read a corrupt target. > > To fix this, change the union of the rcu list head with the children list. > On freeing the eventfs inode, set the is_free and execute a smp_wmb() > before adding the eventfs inode to the SRCU list. > > On iteration of the ei->children list, at the start, execute a smp_rmb() > and then read the is_freed of the ei to see if the children list is still > valid. If is_freed is set, then the ei_child read is not valid and the > loop should exit immediately. > Looks good to me. Reviewed-by: Masami Hiramatsu (Google) <[email protected]> The critical issues Sashiko mentioned will be fixed by Shuangpeng's patch[1]. [1] https://lore.kernel.org/all/[email protected]/ Thank you, > Reported-by: Sashiko <[email protected]> > Closes: > https://sashiko.dev/#/patchset/20260806022719.375354-1-shuangpeng.kernel%40gmail.com > Signed-off-by: Steven Rostedt <[email protected]> > --- > fs/tracefs/event_inode.c | 24 ++++++++++++++++++++++++ > fs/tracefs/internal.h | 4 ++-- > 2 files changed, 26 insertions(+), 2 deletions(-) > > diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c > index 39c7a34531e8..677c39b0d62f 100644 > --- a/fs/tracefs/event_inode.c > +++ b/fs/tracefs/event_inode.c > @@ -124,6 +124,16 @@ static inline void put_ei(struct eventfs_inode *ei) > static inline void free_ei(struct eventfs_inode *ei) > { > if (ei) { > + WARN_ON_ONCE(!list_empty(&ei->children)); > + /* > + * The ei should have no children if it is being freed. > + * The SRCU iteration has a smp_rmb() to make sure it > + * sees a child (that may have already been freed) > + * before it reads is_free. If is_free is set, it must > + * not use the child it acquired from ei->children, as > + * the list may be used for SRCU. > + */ > + smp_wmb(); > ei->is_freed = 1; > put_ei(ei); > } > @@ -627,6 +637,20 @@ static int eventfs_iterate(struct file *file, struct > dir_context *ctx) > list_for_each_entry_srcu(ei_child, &ei->children, list, > srcu_read_lock_held(&eventfs_srcu)) { > > + /* > + * If the ei is being freed, then the ei->children may be > + * being used as the rcu list, which means the next element > + * may be garbage. The ei->is_free is set before switching > + * the ei->children over to ei->rcu. The read memory barrier > + * here makes sure the ei_child is read before is_free is > + * updated. > + * > + * Matches the smp_wmb() in put_ei() > + */ > + smp_rmb(); > + if (ei->is_freed) > + return -EINVAL; > + > if (c > 0) { > c--; > continue; > diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h > index a4a7f8431aff..c61481d04c8e 100644 > --- a/fs/tracefs/internal.h > +++ b/fs/tracefs/internal.h > @@ -46,11 +46,11 @@ struct eventfs_attr { > * @ino: The saved inode number > */ > struct eventfs_inode { > + struct list_head list; > union { > - struct list_head list; > + struct list_head children; > struct rcu_head rcu; > }; > - struct list_head children; > const struct eventfs_entry *entries; > const char *name; > struct eventfs_attr *entry_attrs; > -- > 2.53.0 > -- Masami Hiramatsu (Google) <[email protected]>
