Messages in this thread Patch in this message | | | Date | Sun, 6 Jul 2003 12:03:15 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH][2.5.73] stack corruption in devfs_lookup |
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Andrey Borzenkov <arvidjaar@mail.ru> wrote: > > When devfs_lookup needs to call devfsd it arranges for other lookups for the > same name to wait. It is using local variable as wait queue head. After > devfsd returns devfs_lookup wakes up all waiters and returns. Unfortunately > there is no garantee all waiters will actually get chance to run and clean up > before devfs_lookup returns. so some of them attempt to access already freed > storage on stack.
OK, but I think there is a simpler fix. We can rely on the side-effects of prepare_to_wait() and finish_wait().
The wakeup() will remove all wait_queue_t's from the wait_queue_head, and so when the waiters wake up and call finish_wait(), they will never touch the now-out-of-scope waitqueue head.
It is a little faster than the currentcode, too.
Could you please test this?
diff -puN fs/devfs/base.c~devfs-oops-fix-2 fs/devfs/base.c --- 25/fs/devfs/base.c~devfs-oops-fix-2 2003-07-06 11:55:38.000000000 -0700 +++ 25-akpm/fs/devfs/base.c 2003-07-06 11:59:23.000000000 -0700 @@ -2218,7 +2218,6 @@ static int devfs_d_revalidate_wait (stru struct fs_info *fs_info = dir->i_sb->s_fs_info; devfs_handle_t parent = get_devfs_entry_from_vfs_inode (dir); struct devfs_lookup_struct *lookup_info = dentry->d_fsdata; - DECLARE_WAITQUEUE (wait, current); if ( is_devfsd_or_child (fs_info) ) { @@ -2252,11 +2251,12 @@ static int devfs_d_revalidate_wait (stru read_lock (&parent->u.dir.lock); if (dentry->d_fsdata) { - set_current_state (TASK_UNINTERRUPTIBLE); - add_wait_queue (&lookup_info->wait_queue, &wait); - read_unlock (&parent->u.dir.lock); - schedule (); - remove_wait_queue (&lookup_info->wait_queue, &wait); + DEFINE_WAIT(wait); + + prepare_to_wait(&lookup_info->wait_queue, &wait, TASK_UNINTERRUPTIBLE); + read_unlock(&parent->u.dir.lock); + schedule(); + finish_wait(&lookup_info->wait_queue, &wait); } else read_unlock (&parent->u.dir.lock); return 1; @@ -2336,6 +2336,12 @@ out: dentry->d_op = &devfs_dops; dentry->d_fsdata = NULL; write_lock (&parent->u.dir.lock); + /* + * This wakeup will remove all waiters' wait_queue_t's from the waitqueue + * head, because the waiters use prepare_to_wait()/finished_wait(). + * Hence it is OK that the waitqueue_head goes out of scope immediately + * after the wakeup is delivered + */ wake_up (&lookup_info.wait_queue); write_unlock (&parent->u.dir.lock); devfs_put (de); _
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