On Wed, Jul 3, 2024 at 4:48 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Wed, Jul 03, 2024 at 02:35:49PM GMT, Amir Goldstein wrote:
> > On Wed, Jul 3, 2024 at 7:48 AM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:
> > >
> > > The max count of lowerdir is OVL_MAX_STACK[500], which is broken by
> > > commit 37f32f526438("ovl: fix memory leak in ovl_parse_param()") for
> > > parameter Opt_lowerdir. Since commit 819829f0319a("ovl: refactor layer
> > > parsing helpers") and commit 24e16e385f22("ovl: add support for
> > > appending lowerdirs one by one") added check ovl_mount_dir_check() in
> > > function ovl_parse_param_lowerdir(), the 'ctx->nr' should be smaller
> > > than OVL_MAX_STACK, after commit 37f32f526438("ovl: fix memory leak in
> > > ovl_parse_param()") is applied, the 'ctx->nr' is updated before the
> > > check ovl_mount_dir_check(), which leads the max count of lowerdir
> > > to become 499 for parameter Opt_lowerdir.
> > > Fix it by updating 'ctx->nr' after the check ovl_mount_dir_check().
> > >
> > > Fixes: 37f32f526438 ("ovl: fix memory leak in ovl_parse_param()")
> > > Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
> > > ---
> > > fs/overlayfs/params.c | 6 ++++--
> > > 1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
> > > index 4860fcc4611b..0d8c456aa8fa 100644
> > > --- a/fs/overlayfs/params.c
> > > +++ b/fs/overlayfs/params.c
> > > @@ -486,7 +486,6 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
> > > iter = dup;
> > > l = ctx->lower;
> > > for (nr = 0; nr < nr_lower; nr++, l++) {
> > > - ctx->nr++;
> > > memset(l, 0, sizeof(*l));
> > >
> > > err = ovl_mount_dir(iter, &l->path);
> > > @@ -494,9 +493,12 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
> > > goto out_put;
> > >
> > > err = ovl_mount_dir_check(fc, &l->path, Opt_lowerdir, iter, false);
> > > - if (err)
> > > + if (err) {
> > > + path_put(&l->path);
> > > goto out_put;
> > > + }
> > >
> > > + ctx->nr++;
> > > err = -ENOMEM;
> > > l->name = kstrdup(iter, GFP_KERNEL_ACCOUNT);
> > > if (!l->name)
> > > --
> > > 2.39.2
> > >
> >
> > This fix looks correct, but it is not pretty IMO.
> > The cleanup on error is much cleaner in ovl_parse_layer() -> ovl_add_layer()
> > I wonder if we can reuse some of those helpers instead of the current code.
> >
> > Christian, what do you think?
>
> Yeah, sounds good. Something like the completely untested below.
> Feel free to reuse in whatever form.
This looks much nicer!
I think you unintentionally dropped incrementing of ctx->nr_data
for the notorious case of ::<lowerdatadir>.
Zhihao,
Please make sure to run the fstests overlay test for lowerdatadirs
overlay/079 overlay/085 overlay/086
Thanks,
Amir.
