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From: 139 <cgxu519@139.com>
To: Zheng Liang <zhengliang6@huawei.com>
Cc: miklos@szeredi.hu, linux-unionfs@vger.kernel.org, yi.zhang@huawei.com
Subject: Re: [PATCH] ovl: fix oops in ovl_rename
Date: Fri, 24 Sep 2021 15:12:03 +0800	[thread overview]
Message-ID: <E376E38A-ABB0-4E20-B7C8-980F8CFC2047@139.com> (raw)
In-Reply-To: <20210924011628.2069334-1-zhengliang6@huawei.com>

在 2021年9月24日,09:09,Zheng Liang <zhengliang6@huawei.com> 写道:
> 
> We find a kernel NULL pointer dereference problem in overlayfs.
> The problem can appear in the following scene:
> 
> mkdir lower upper work merge
> touch lower/old
> touch lower/new
> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merge
> rm merge/new
> ------------------------------------------------------------------------------------------
> process A(rename file in merge)                                process B(delete file in upper)
> renameat2(AT_FDCWD, "old", AT_FDCWD, "new", 0)
> (new is whiteout file in upper)
>  do_renameat2
>    vfs_rename
>      ovl_rename
>      (overwrite=true,ovl_lower_positive(old)=true,
>      ovl_dentry_is_whiteout(new)=true)
>      (we can add some delay after "flags|=RENAME_EXCHANGE",
>      it can make the problem appear more easy)
>      ……                                                       unlink(new)
>      ……                                                       (delete whiteout in upper)
>      (newdentry is negative)
>        ovl_do_rename

Is it a real use case? I believe there will be many unexpected behaviors if you delete the files in upper layer deliberately.

Thanks,
Chengguang



> 
> So,before commencing with ovl_do_rename that the flags maybe attach RENAME_EXCHANGE
> and the newdentry is negative in ovl_rename.If we enabled selinux,it
> will lead to kernel panic.such as the following log:
> PID: 2552045  TASK: ffff8880302faf00  CPU: 2   COMMAND: "fsstress"
> #0 [ffff888080e772a0] machine_kexec at ffffffff856adedc
> #1 [ffff888080e773a8] __crash_kexec at ffffffff8585cd20
> #2 [ffff888080e774c0] panic at ffffffff8572b288
> #3 [ffff888080e77590] oops_end at ffffffff85641f6e
> #4 [ffff888080e775f0] __do_page_fault at ffffffff856cd55b
> #5 [ffff888080e77668] do_page_fault at ffffffff856cd834
> #6 [ffff888080e776a0] async_page_fault at ffffffff8660125e
>    [exception RIP: __inode_security_revalidate+34]
>    RIP: ffffffff85c43452  RSP: ffff888080e77758  RFLAGS: 00010202
>    RAX: 0000000000000000  RBX: 0000000000000000  RCX: ffffffff8593ae7e
>    RDX: 0000000000000000  RSI: 0000000000000297  RDI: 0000000000000297
>    RBP: ffff8881984e6628   R8: ffffed10115e3f39   R9: ffffed10115e3f39
>    R10: 0000000000000001  R11: ffffed10115e3f38  R12: 0000000000000001
>    R13: 0000000000000000  R14: ffff88808350a000  R15: 1ffff110101ceef5
>    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
> #7 [ffff888080e77780] selinux_inode_rename at ffffffff85c4418d
> #8 [ffff888080e77858] security_inode_rename at ffffffff85c35f24
> #9 [ffff888080e77890] vfs_rename at ffffffff85b01209
> #10 [ffff888080e779a8] ovl_do_rename at ffffffffc0a44c22 [overlay]
> #11 [ffff888080e779d8] ovl_rename at ffffffffc0a46575 [overlay]
> #12 [ffff888080e77b48] vfs_rename at ffffffff85b0155a
> #13 [ffff888080e77c60] do_renameat2 at ffffffff85b06e65
> #14 [ffff888080e77f00] __x64_sys_renameat2 at ffffffff85b06fb2
> #15 [ffff888080e77f30] do_syscall_64 at ffffffff85606243
> #16 [ffff888080e77f50] entry_SYSCALL_64_after_hwframe at ffffffff866000ad
> 
> We can add some check in ovl_rename for this scene and return error to avoid kernel panic.
> 
> Signed-off-by: Zheng Liang <zhengliang6@huawei.com>
> ---
> fs/overlayfs/dir.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 1fefb2b8960e..93c7c267de93 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -1219,9 +1219,13 @@ static int ovl_rename(struct user_namespace *mnt_userns, struct inode *olddir,
>                goto out_dput;
>        }
>    } else {
> -        if (!d_is_negative(newdentry) &&
> -            (!new_opaque || !ovl_is_whiteout(newdentry)))
> -            goto out_dput;
> +        if (!d_is_negative(newdentry)) {
> +            if (!new_opaque || !ovl_is_whiteout(newdentry))
> +                goto out_dput;
> +        } else {
> +            if (flags & RENAME_EXCHANGE)
> +                goto out_dput;
> +        }
>    }
> 
>    if (olddentry == trap)
> -- 
> 2.25.4
> 



  reply	other threads:[~2021-09-24  7:21 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-24  1:16 Zheng Liang
2021-09-24  7:12 ` 139 [this message]
2021-09-24  8:50   ` zhengliang (A)
2021-09-24 19:01 ` Miklos Szeredi

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