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?
Thanks,
Amir.
