[PATCH] jffs2: fix UAF problem

[Joakim Tjernlund]

Maintainer ping ?

   Jocke

On Wed, 2020-06-24 at 18:59 +0000, Joakim Tjernlund wrote:
> 
> Nice find, I just came across a deadlock wrt GC and rmdir,
> hopefully this is he fix.
> 
> This needs to go to stable too, sooner rather than later.
> 
>  Jocke
> 
> On Fri, 2020-06-19 at 17:06 +0800, Zhe Li wrote:
> > 
> > The log of UAF problem is listed below.
> > BUG: KASAN: use-after-free in jffs2_rmdir+0xa4/0x1cc [jffs2] at addr c1f165fc
> > Read of size 4 by task rm/8283
> > =============================================================================
> > BUG kmalloc-32 (Tainted: P    B      O   ): kasan: bad access detected
> > -----------------------------------------------------------------------------
> > 
> > INFO: Allocated in 0xbbbbbbbb age=3054364 cpu=0 pid=0
> >         0xb0bba6ef
> >         jffs2_write_dirent+0x11c/0x9c8 [jffs2]
> >         __slab_alloc.isra.21.constprop.25+0x2c/0x44
> >         __kmalloc+0x1dc/0x370
> >         jffs2_write_dirent+0x11c/0x9c8 [jffs2]
> >         jffs2_do_unlink+0x328/0x5fc [jffs2]
> >         jffs2_rmdir+0x110/0x1cc [jffs2]
> >         vfs_rmdir+0x180/0x268
> >         do_rmdir+0x2cc/0x300
> >         ret_from_syscall+0x0/0x3c
> > INFO: Freed in 0x205b age=3054364 cpu=0 pid=0
> >         0x2e9173
> >         jffs2_add_fd_to_list+0x138/0x1dc [jffs2]
> >         jffs2_add_fd_to_list+0x138/0x1dc [jffs2]
> >         jffs2_garbage_collect_dirent.isra.3+0x21c/0x288 [jffs2]
> >         jffs2_garbage_collect_live+0x16bc/0x1800 [jffs2]
> >         jffs2_garbage_collect_pass+0x678/0x11d4 [jffs2]
> >         jffs2_garbage_collect_thread+0x1e8/0x3b0 [jffs2]
> >         kthread+0x1a8/0x1b0
> >         ret_from_kernel_thread+0x5c/0x64
> > Call Trace:
> > [c17ddd20] [c02452d4] kasan_report.part.0+0x298/0x72c (unreliable)
> > [c17ddda0] [d2509680] jffs2_rmdir+0xa4/0x1cc [jffs2]
> > [c17dddd0] [c026da04] vfs_rmdir+0x180/0x268
> > [c17dde00] [c026f4e4] do_rmdir+0x2cc/0x300
> > [c17ddf40] [c001a658] ret_from_syscall+0x0/0x3c
> > 
> > The root cause is that we don't get "jffs2_inode_info.sem" before
> > we scan list "jffs2_inode_info.dents" in function jffs2_rmdir.
> > This patch add codes to get "jffs2_inode_info.sem" before we scan
> > "jffs2_inode_info.dents" to slove the UAF problem.
> > 
> > Signed-off-by: Zhe Li <lizhe67 at huawei.com>
> > ---
> >  fs/jffs2/dir.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/jffs2/dir.c b/fs/jffs2/dir.c
> > index f20cff1..7764937 100644
> > --- a/fs/jffs2/dir.c
> > +++ b/fs/jffs2/dir.c
> > @@ -590,10 +590,14 @@ static int jffs2_rmdir (struct inode *dir_i, struct dentry *dentry)
> >         int ret;
> >         uint32_t now = JFFS2_NOW();
> > 
> > +       mutex_lock(&f->sem);
> >         for (fd = f->dents ; fd; fd = fd->next) {
> > -               if (fd->ino)
> > +               if (fd->ino) {
> > +                       mutex_unlock(&f->sem);
> >                         return -ENOTEMPTY;
> > +               }
> >         }
> > +       mutex_unlock(&f->sem);
> > 
> >         ret = jffs2_do_unlink(c, dir_f, dentry->d_name.name,
> >                               dentry->d_name.len, f, now);
> > --
> > 2.7.4
> > 
> > 
> >