[Devel] [PATCH v2 v2] fs/ovelayfs: Fix crash on overlayfs mount
Alexander Mikhalitsyn
alexander.mikhalitsyn at virtuozzo.com
Fri Jan 22 13:17:14 MSK 2021
On Mon, 18 Jan 2021 15:47:26 +0300
Andrey Ryabinin <aryabinin at virtuozzo.com> wrote:
> Kdump kernel fails to load because of crash on mount of overlayfs:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000060
> ....
> Call Trace:
> seq_path+0x64/0xb0
> print_paths_option+0x79/0xa0
> ovl_show_options+0x3a/0x320
> show_mountinfo+0x1ee/0x290
> seq_read+0x2f8/0x400
> vfs_read+0x9d/0x150
> ksys_read+0x4f/0xb0
> do_syscall_64+0x5b/0x1a0
>
> This is cause by OOB access of ofs->lowerpaths.
> We transfer to print_paths_option() ofs->numlayer as size of ->lowerpaths
> array, but it's not.
>
> The correct number of lowerpaths elements is ->numlower in 'struct ovl_entry'.
> So move lowerpaths there and use oe->numlower as array size.
>
> Fixes: 17fc61697f73 ("overlayfs: add dynamic path resolving in mount options")
> Fixes: 2191d729083d ("overlayfs: add mnt_id paths options")
>
> https://jira.sw.ru/browse/PSBM-123508
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
Reviewed-by: Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
> ---
> fs/overlayfs/ovl_entry.h | 2 +-
> fs/overlayfs/super.c | 37 ++++++++++++++++++++-----------------
> 2 files changed, 21 insertions(+), 18 deletions(-)
>
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index ea1906448ec5..2315089a0211 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -54,7 +54,6 @@ struct ovl_fs {
> unsigned int numlayer;
> /* Number of unique fs among layers including upper fs */
> unsigned int numfs;
> - struct path *lowerpaths;
> const struct ovl_layer *layers;
> struct ovl_sb *fs;
> /* workbasepath is the path at workdir= mount option */
> @@ -98,6 +97,7 @@ struct ovl_entry {
> struct rcu_head rcu;
> };
> unsigned numlower;
> + struct path *lowerpaths;
> struct ovl_path lowerstack[];
> };
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 3755f280036f..fb419617564c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -70,8 +70,12 @@ static void ovl_entry_stack_free(struct ovl_entry *oe)
> {
> unsigned int i;
>
> - for (i = 0; i < oe->numlower; i++)
> + for (i = 0; i < oe->numlower; i++) {
> dput(oe->lowerstack[i].dentry);
> + if (oe->lowerpaths)
> + path_put(&oe->lowerpaths[i]);
> + }
> + kfree(oe->lowerpaths);
> }
>
> static bool ovl_metacopy_def = IS_ENABLED(CONFIG_OVERLAY_FS_METACOPY);
> @@ -241,11 +245,6 @@ static void ovl_free_fs(struct ovl_fs *ofs)
> ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
> mntput(ofs->upper_mnt);
> path_put(&ofs->upperpath);
> - if (ofs->lowerpaths) {
> - for (i = 0; i < ofs->numlayer; i++)
> - path_put(&ofs->lowerpaths[i]);
> - kfree(ofs->lowerpaths);
> - }
> for (i = 1; i < ofs->numlayer; i++) {
> iput(ofs->layers[i].trap);
> mntput(ofs->layers[i].mnt);
> @@ -359,9 +358,10 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> {
> struct super_block *sb = dentry->d_sb;
> struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_entry *oe = OVL_E(dentry);
>
> if (ovl_dyn_path_opts) {
> - print_paths_option(m, "lowerdir", ofs->lowerpaths, ofs->numlayer);
> + print_paths_option(m, "lowerdir", oe->lowerpaths, oe->numlower);
> if (ofs->config.upperdir) {
> print_path_option(m, "upperdir", &ofs->upperpath);
> print_path_option(m, "workdir", &ofs->workbasepath);
> @@ -375,7 +375,7 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
> }
>
> if (ovl_mnt_id_path_opts) {
> - print_mnt_ids_option(m, "lowerdir_mnt_id", ofs->lowerpaths, ofs->numlayer);
> + print_mnt_ids_option(m, "lowerdir_mnt_id", oe->lowerpaths, oe->numlower);
> /*
> * We don't need to show mnt_id for workdir because it
> * on the same mount as upperdir.
> @@ -1626,6 +1626,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> int err;
> char *lowertmp, *lower;
> unsigned int stacklen, numlower = 0, i;
> + struct path *stack = NULL;
> struct ovl_entry *oe;
>
> err = -ENOMEM;
> @@ -1649,14 +1650,14 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> }
>
> err = -ENOMEM;
> - ofs->lowerpaths = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
> - if (!ofs->lowerpaths)
> + stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
> + if (!stack)
> goto out_err;
>
> err = -EINVAL;
> lower = lowertmp;
> for (numlower = 0; numlower < stacklen; numlower++) {
> - err = ovl_lower_dir(lower, &ofs->lowerpaths[numlower], ofs,
> + err = ovl_lower_dir(lower, &stack[numlower], ofs,
> &sb->s_stack_depth);
> if (err)
> goto out_err;
> @@ -1671,7 +1672,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> goto out_err;
> }
>
> - err = ovl_get_layers(sb, ofs, ofs->lowerpaths, numlower);
> + err = ovl_get_layers(sb, ofs, stack, numlower);
> if (err)
> goto out_err;
>
> @@ -1681,9 +1682,10 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> goto out_err;
>
> for (i = 0; i < numlower; i++) {
> - oe->lowerstack[i].dentry = dget(ofs->lowerpaths[i].dentry);
> + oe->lowerstack[i].dentry = dget(stack[i].dentry);
> oe->lowerstack[i].layer = &ofs->layers[i+1];
> }
> + oe->lowerpaths = stack;
>
> out:
> kfree(lowertmp);
> @@ -1691,10 +1693,11 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> return oe;
>
> out_err:
> - for (i = 0; i < numlower; i++)
> - path_put_init(&ofs->lowerpaths[i]);
> - kfree(ofs->lowerpaths);
> - ofs->lowerpaths = NULL;
> + if (stack) {
> + for (i = 0; i < numlower; i++)
> + path_put(&stack[i]);
> + kfree(stack);
> + }
> oe = ERR_PTR(err);
> goto out;
> }
> --
> 2.26.2
>
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--
Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
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