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, Amir.
