On Fri, Feb 14, 2025 at 10:51 PM Vasiliy Kovalev <kovalev@xxxxxxxxxxxx> wrote:
>
> The issue was caused by dput(upper) being called before
> ovl_dentry_update_reval(), while upper->d_flags was still
> accessed in ovl_dentry_remote().
>
> Move dput(upper) after its last use to prevent use-after-free.
>
> BUG: KASAN: slab-use-after-free in ovl_dentry_remote fs/overlayfs/util.c:162 [inline]
> BUG: KASAN: slab-use-after-free in ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167
>
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114
> print_address_description mm/kasan/report.c:377 [inline]
> print_report+0xc3/0x620 mm/kasan/report.c:488
> kasan_report+0xd9/0x110 mm/kasan/report.c:601
> ovl_dentry_remote fs/overlayfs/util.c:162 [inline]
> ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167
> ovl_link_up fs/overlayfs/copy_up.c:610 [inline]
> ovl_copy_up_one+0x2105/0x3490 fs/overlayfs/copy_up.c:1170
> ovl_copy_up_flags+0x18d/0x200 fs/overlayfs/copy_up.c:1223
> ovl_rename+0x39e/0x18c0 fs/overlayfs/dir.c:1136
> vfs_rename+0xf84/0x20a0 fs/namei.c:4893
> ...
> </TASK>
>
> Fixes: b07d5cc93e1b ("ovl: update of dentry revalidate flags after copy up")
> Reported-by: syzbot+316db8a1191938280eb6@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=316db8a1191938280eb6
> Signed-off-by: Vasiliy Kovalev <kovalev@xxxxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
Christian,
Could you pick this up via vfs.fixes?
Thanks,
Amir.
> ---
> fs/overlayfs/copy_up.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 0c28e5fa34077..d7310fcf38881 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -618,7 +618,6 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
> err = PTR_ERR(upper);
> if (!IS_ERR(upper)) {
> err = ovl_do_link(ofs, ovl_dentry_upper(c->dentry), udir, upper);
> - dput(upper);
>
> if (!err) {
> /* Restore timestamps on parent (best effort) */
> @@ -626,6 +625,7 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
> ovl_dentry_set_upper_alias(c->dentry);
> ovl_dentry_update_reval(c->dentry, upper);
> }
> + dput(upper);
> }
> inode_unlock(udir);
> if (err)
> --
> 2.42.2
>
