On Tue, May 16, 2023 at 3:27 PM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote: > > 在 2023/5/16 19:45, Amir Goldstein 写道: > > On Tue, May 16, 2023 at 4:16 AM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote: > >> > >> 在 2023/5/15 23:36, Amir Goldstein 写道: > >>> On Mon, May 15, 2023 at 6:16 PM Christian Brauner <brauner@xxxxxxxxxx> wrote: > >>>> > >>>> On Mon, May 15, 2023 at 05:58:55PM +0300, Amir Goldstein wrote: > >>>>> On Mon, May 15, 2023 at 4:58 PM Christian Brauner <brauner@xxxxxxxxxx> wrote: > >>>>>> > >>>>>> On Mon, May 15, 2023 at 09:36:28PM +0800, Zhihao Cheng wrote: > >>>>>>> Following process: > >>>>>>> P1 P2 > >>>>>>> path_lookupat > >>>>>>> link_path_walk > >>>>>>> inode_permission > >>>>>>> ovl_permission > >>>>>>> ovl_i_path_real(inode, &realpath) > >>>>>>> path->dentry = ovl_i_dentry_upper(inode) > >>>>>>> drop_cache > >>>>>>> __dentry_kill(ovl_dentry) > >>>>>>> iput(ovl_inode) > >>>>>>> ovl_destroy_inode(ovl_inode) > >>>>>>> dput(oi->__upperdentry) > >>>>>>> dentry_kill(upperdentry) > >>>>>>> dentry_unlink_inode > >>>>>>> upperdentry->d_inode = NULL > >>>>>>> realinode = d_inode(realpath.dentry) // return NULL > >>>>>>> inode_permission(realinode) > >>>>>>> inode->i_sb // NULL pointer dereference > >>>>>>> , will trigger an null pointer dereference at realinode: > >>>>>>> [ 335.664979] BUG: kernel NULL pointer dereference, > >>>>>>> address: 0000000000000002 > >>>>>>> [ 335.668032] CPU: 0 PID: 2592 Comm: ls Not tainted 6.3.0 > >>>>>>> [ 335.669956] RIP: 0010:inode_permission+0x33/0x2c0 > >>>>>>> [ 335.678939] Call Trace: > >>>>>>> [ 335.679165] <TASK> > >>>>>>> [ 335.679371] ovl_permission+0xde/0x320 > >>>>>>> [ 335.679723] inode_permission+0x15e/0x2c0 > >>>>>>> [ 335.680090] link_path_walk+0x115/0x550 > >>>>>>> [ 335.680771] path_lookupat.isra.0+0xb2/0x200 > >>>>>>> [ 335.681170] filename_lookup+0xda/0x240 > >>>>>>> [ 335.681922] vfs_statx+0xa6/0x1f0 > >>>>>>> [ 335.682233] vfs_fstatat+0x7b/0xb0 > >>>>>>> > >>>>>>> Fetch a reproducer in [Link]. > >>>>>>> > >>>>>>> Add a new helper ovl_i_path_realinode() to get realpath and real inode > >>>>>>> after non-nullptr checking, use the helper to replace the current realpath > >>>>>>> getting logic. > >>>>>>> > >>>>>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217405 > >>>>>>> Fixes: 4b7791b2e958 ("ovl: handle idmappings in ovl_permission()") > >>>>>>> Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx> > >>>>>>> Suggested-by: Christian Brauner <brauner@xxxxxxxxxx> > >>>>>>> --- > >>>>>>> fs/overlayfs/inode.c | 31 ++++++++++++++++++++++++------- > >>>>>>> 1 file changed, 24 insertions(+), 7 deletions(-) > >>>>>>> > >>>>>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c > >>>>>>> index 541cf3717fc2..cc3ef5a6666a 100644 > >>>>>>> --- a/fs/overlayfs/inode.c > >>>>>>> +++ b/fs/overlayfs/inode.c > >>>>>>> @@ -278,6 +278,26 @@ int ovl_getattr(struct mnt_idmap *idmap, const struct path *path, > >>>>>>> return err; > >>>>>>> } > >>>>>>> > >>>>>>> +static inline int ovl_i_path_realinode(struct inode *inode, > >>>>>>> + struct path *realpath, > >>>>>>> + struct inode **realinode, int rcu) > >>>>>>> +{ > >>>>>>> + /* Careful in RCU walk mode */ > >>>>>>> + ovl_i_path_real(inode, realpath); > >>>>>>> + if (!realpath->dentry) { > >>>>>>> + WARN_ON(!rcu); > >>>>>>> + return -ECHILD; > >>>>>>> + } > >>>>>>> + > >>>>>>> + *realinode = d_inode(realpath->dentry); > >>>>>>> + if (!*realinode) { > >>>>>>> + WARN_ON(!rcu); > >>>>>>> + return -ECHILD; > >>>>>>> + } > >>>>>>> + > >>>>>>> + return 0; > >>>>>>> +} > >>>>>> > >>>>>> If you want to return the inode wouldn't it possibly make more sense to > >>>>>> return the inode from the function directly? But not fuzzed. Maybe Amir > >>>>>> has a preference. As I said, I'm even fine with the original approach. > >>>>> > >>>>> Sorry for not reviewing v1, I was traveling, even though it is hard to use > >>>>> this excuse when I was traveling with Christian who did review v1 :) > >>>> > >>>> Well, I did only do it this morning. :) > >>>> > >>>>> > >>>>>> > >>>>>> static inline struct inode *ovl_i_path_realinode(struct inode *inode, > >>>>>> struct path *realpath, > >>>>>> int rcu) > >>>>>> { > >>>>>> struct inode *realinode; > >>>>>> > >>>>>> /* Careful in RCU walk mode */ > >>>>>> ovl_i_path_real(inode, realpath); > >>>>>> if (!realpath->dentry) { > >>>>>> WARN_ON(!rcu); > >>>>>> return ERR_PTR(-ECHILD); > >>>>>> } > >>>>>> > >>>>>> realinode = d_inode(realpath->dentry); > >>>>>> if (!realinode) { > >>>>>> WARN_ON(!rcu); > >>>>>> return ERR_PTR(-ECHILD); > >>>>>> } > >>>>>> > >>>>>> return realinode; > >>>>>> } > >>>>>> > >>>>> > >>>>> I think this helper is over engineered ;-) > >>>> > >>>> Yes. As mentioned before, I would've been happy even with v1 that didn't > >>>> have any helper. > >>>> > >>>>> The idea for a helper that returns inode is good, > >>>>> but I see no reason to mix RCU walk in this helper > >>>>> and don't even need a new helper (see untested patch below). > >>>> > >>>> Looks good to me too. > >>>> > >>>>> > >>>>> Thanks, > >>>>> Amir. > >>>>> > >>>>> --- > >>>>> -void ovl_i_path_real(struct inode *inode, struct path *path) > >>>>> +struct inode *ovl_i_path_real(struct inode *inode, struct path *path) > >>>>> { > >>>>> struct ovl_path *lowerpath = ovl_lowerpath(OVL_I_E(inode)); > >>>>> > >>>>> @@ -342,6 +342,8 @@ void ovl_i_path_real(struct inode *inode, struct path *path) > >>>>> } else { > >>>>> path->mnt = ovl_upper_mnt(OVL_FS(inode->i_sb)); > >>>>> } > >>>>> + > >>>>> + return path->dentry ? d_inode(path->dentry) : NULL; > >>>>> } > >>>>> > >>>>> @@ -295,8 +295,8 @@ int ovl_permission(struct mnt_idmap *idmap, > >>>>> int err; > >>>>> > >>>>> /* Careful in RCU walk mode */ > >>>>> - ovl_i_path_real(inode, &realpath); > >>>>> - if (!realpath.dentry) { > >>>>> + realinode = ovl_i_path_real(inode, &realpath); > >>>>> + if (!realpath.dentry || !realinode) { > >>>>> WARN_ON(!(mask & MAY_NOT_BLOCK)); > >>>>> return -ECHILD; > >>>>> } > >>>>> @@ -309,7 +309,6 @@ int ovl_permission(struct mnt_idmap *idmap, > >>>>> > >>>>> if (err) > >>>>> return err; > >>>>> > >>>>> - realinode = d_inode(realpath.dentry); > >>>>> old_cred = ovl_override_creds(inode->i_sb); > >>>> > >> > >> Thanks for reviewings and helpful discussion from Amir and Christian. > >> > > > > You're welcome. > > > > Note to self: there is be a trivial conflict with the change to > > ovl_i_path_real() > > return type and this patch from my ovl-lazy-lowerdata series: > > https://lore.kernel.org/linux-unionfs/20230427130539.2798797-7-amir73il@xxxxxxxxx/ > > > > After Miklos takes your fixes, I will rebase. > > Thanks for rebasing, so you will take v2 with modified helper > ovl_i_path_real(return realinode)? > Please post v3 with the modified helper for Miklos to take. Thanks, Amir.
