| Message ID | 20200610130422.1197386-1-gladkov.alexey@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | proc: s_fs_info may be NULL when proc_kill_sb is called | expand |
Alexey Gladkov <gladkov.alexey@gmail.com> 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@google.com > Reported-by: syzbot+4abac52934a48af5ff19@syzkaller.appspotmail.com > Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace") > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> > --- > 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 = {
On Wed, Jun 10, 2020 at 12:12:54PM -0500, Eric W. Biederman wrote: > > { > > 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); While we are at it, dput(NULL) is an explicit no-op.
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 = {
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. Link: https://lore.kernel.org/lkml/0000000000002d7ca605a7b8b1c5@google.com Reported-by: syzbot+4abac52934a48af5ff19@syzkaller.appspotmail.com Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace") Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> --- fs/proc/root.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)