Alexey Gladkov <gladkov.alexey@xxxxxxxxx> writes: > syzbot found that proc_fill_super() fails before filling up sb->s_fs_info, > deactivate_locked_super() will be called and sb->s_fs_info will be NULL. > The proc_kill_sb() does not expect fs_info to be NULL which is wrong. For the case where s_fs_info is never allocated this looks correct. That is because generic_shutdown_super has a special for !sb->s_root. However for the existing cases I can't convince myself that it is safe to change the order we free the pid namespace and free fs_info. There is a lot of code that can run while generic_shutdown_super is running and purging all of the inodes. We have crazy things like proc_flush_pid that might care, as well proc_evict_inode. I haven't found anything that actually references fs_info or actually depends on the pid namespace living longer than the proc inode but it would be really easy to miss something. Can you send a v2 version does not change the order things are freed in for the case where we do allocate fs_info. That will make it trivially safe to apply. Otherwise this looks like a very good patch. Thank you, Eric > Link: https://lore.kernel.org/lkml/0000000000002d7ca605a7b8b1c5@xxxxxxxxxx > Reported-by: syzbot+4abac52934a48af5ff19@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace") > Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx> > --- > fs/proc/root.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/fs/proc/root.c b/fs/proc/root.c > index ffebed1999e5..a715eb9f196a 100644 > --- a/fs/proc/root.c > +++ b/fs/proc/root.c > @@ -264,15 +264,18 @@ static void proc_kill_sb(struct super_block *sb) > { > struct proc_fs_info *fs_info = proc_sb_info(sb); > > - if (fs_info->proc_self) > - dput(fs_info->proc_self); > + if (fs_info) { > + if (fs_info->proc_self) > + dput(fs_info->proc_self); > > - if (fs_info->proc_thread_self) > - dput(fs_info->proc_thread_self); > + if (fs_info->proc_thread_self) > + dput(fs_info->proc_thread_self); > + > + put_pid_ns(fs_info->pid_ns); > + kfree(fs_info); > + } > > kill_anon_super(sb); > - put_pid_ns(fs_info->pid_ns); > - kfree(fs_info); > } > > static struct file_system_type proc_fs_type = {
