linux-kernel - Re: [PATCH AUTOSEL 4.19 138/172] ovl: verify permissions in ovl_path

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Date:   Tue, 23 Jun 2020 21:05:37 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        linux- stable <stable@...r.kernel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        linux-unionfs@...r.kernel.org, lkft-triage@...ts.linaro.org,
        LTP List <ltp@...ts.linux.it>
Subject: Re: [PATCH AUTOSEL 4.19 138/172] ovl: verify permissions in ovl_path_open()

On Thu, 18 Jun 2020 at 07:16, Sasha Levin <sashal@...nel.org> wrote:
>
> From: Miklos Szeredi <mszeredi@...hat.com>
>
> [ Upstream commit 56230d956739b9cb1cbde439d76227d77979a04d ]
>
> Check permission before opening a real file.
>
> ovl_path_open() is used by readdir and copy-up routines.
>
> ovl_permission() theoretically already checked copy up permissions, but it
> doesn't hurt to re-do these checks during the actual copy-up.
>
> For directory reading ovl_permission() only checks access to topmost
> underlying layer.  Readdir on a merged directory accesses layers below the
> topmost one as well.  Permission wasn't checked for these layers.
>
> Note: modifying ovl_permission() to perform this check would be far more
> complex and hence more bug prone.  The result is less precise permissions
> returned in access(2).  If this turns out to be an issue, we can revisit
> this bug.
>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  fs/overlayfs/util.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index db8bdb29b320..afbc6a97da2a 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -479,7 +479,32 @@ bool ovl_is_whiteout(struct dentry *dentry)
>
>  struct file *ovl_path_open(struct path *path, int flags)
>  {
> -       return dentry_open(path, flags | O_NOATIME, current_cred());
> +       struct inode *inode = d_inode(path->dentry);
> +       int err, acc_mode;
> +
> +       if (flags & ~(O_ACCMODE | O_LARGEFILE))
> +               BUG();

This BUG: triggered on stable-rc 5.7, 5.4, 4.19 and 4.14 on arm64 architecture.

steps to reproduce:
          - cd /opt/ltp
          - ./runltp -s execveat03

tst_device.c:262: INFO: Using test device LTP_DEV='/dev/loop0'
tst_mkfs.c:90: INFO: Formatting /dev/loop0 with ext2 opts='' extra opts=''
mke2fs 1.43.8 (1-Jan-2018)
[  407.103235] ------------[ cut here ]------------
[  407.107890] kernel BUG at fs/overlayfs/util.c:486!
[  407.112704] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[  407.118209] Modules linked in: overlay rfkill crc32_ce crct10dif_ce fuse
[  407.124965] Process execveat03 (pid: 17583, stack limit = 0x0000000043f145d5)
[  407.132136] CPU: 5 PID: 17583 Comm: execveat03 Not tainted
4.19.130-rc1-00442-g6c3e013be752 #1
[  407.140774] Hardware name: ARM Juno development board (r2) (DT)
[  407.146718] pstate: 60000005 (nZCv daif -PAN -UAO)
[  407.151634] pc : ovl_path_open+0xc4/0xc8 [overlay]
[  407.156537] lr : ovl_path_open+0x2c/0xc8 [overlay]
[  407.161345] sp : ffff800909eaf8c0
[  407.164673] x29: ffff800909eaf8c0 x28: ffff800909eafb40
[  407.170011] x27: 0000000000000000 x26: ffff2000012de1c0
[  407.175349] x25: ffff800909785e6c x24: ffff8009042073f0
[  407.180687] x23: ffff800909eafb40 x22: ffff200009d4d8c8
[  407.186026] x21: ffff800909eafb40 x20: ffff8008e4e25238
[  407.191364] x19: 0000000000004000 x18: 0000000000000000
[  407.196700] x17: 0000000000000000 x16: 0000000000000000
[  407.202037] x15: 0000000000000000 x14: ffff200008340864
[  407.207375] x13: ffff20000833f61c x12: ffff20000833b7bc
[  407.212714] x11: ffff20000830c52c x10: ffff2000012c8158
[  407.218052] x9 : ffff20000830b12c x8 : ffff200008084788
[  407.223390] x7 : 0000000041b58ab3 x6 : 00000000f1f1f1f1
[  407.228726] x5 : 00000000f3000000 x4 : dfff200000000000
[  407.234064] x3 : dfff200000000000 x2 : 0000000000000007
[  407.239401] x1 : 0000000000004000 x0 : 0000000000000000
[  407.244736] Call trace:
[  407.247289]  ovl_path_open+0xc4/0xc8 [overlay]
[  407.251846]  ovl_check_d_type_supported+0x9c/0x178 [overlay]
[  407.257616]  ovl_fill_super+0x8d4/0x1ad8 [overlay]
[  407.262437]  mount_nodev+0x4c/0xb8
[  407.265942]  ovl_mount+0x18/0x20 [overlay]
[  407.270060]  mount_fs+0x64/0x1d8
[  407.273314]  vfs_kern_mount.part.0+0x4c/0x1a0
[  407.277696]  do_mount+0x27c/0x1080
[  407.281121]  ksys_mount+0x8c/0xe8
[  407.284459]  __arm64_sys_mount+0x64/0x80
[  407.288409]  el0_svc_common+0xac/0x1e8
[  407.292182]  el0_svc_handler+0x38/0x80
[  407.295951]  el0_svc+0x8/0xc
[  407.298859] Code: f94013f5 a8c37bfd d65f03c0 d4210000 (d4210000)
[  407.304977] ---[ end trace 50a1985db0cfa610 ]---

https://lkft.validation.linaro.org/scheduler/job/1515127#L3772

metadata:
  git branch: linux-4.19.y
  git repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
  git commit: 6c3e013be752bf70e7321d7c813d68eac8ac36b0
  git describe: v4.19.128-442-g6c3e013be752
  make_kernelversion: 4.19.130-rc1
  kernel-config:
https://builds.tuxbuild.com/xGjDe8DWEXpxwsygVrqa6Q/kernel.config
  build-url: https://gitlab.com/Linaro/lkft/kernel-runs/-/pipelines/158883698

-- 
Linaro LKFT
https://lkft.linaro.org