linux-kernel - Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in ovl_path

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Date:   Tue, 23 Jun 2020 20:55:38 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Sasha Levin <sashal@...nel.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
Subject: Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in ovl_path_open()

On Thu, 18 Jun 2020 at 07:18, 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 afdc2533ce74..76d6610767f6 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -307,7 +307,32 @@ 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();
> +
> +       switch (flags & O_ACCMODE) {
> +       case O_RDONLY:
> +               acc_mode = MAY_READ;
> +               break;
> +       case O_WRONLY:
> +               acc_mode = MAY_WRITE;
> +               break;
> +       default:
> +               BUG();

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

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

Test output:
mke2fs 1.43.8 (1-Jan-2018)
[   47.739682] ------------[ cut here ]------------
[   47.744317] kernel BUG at fs/overlayfs/util.c:314!
[   47.749117] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[   47.754608] Modules linked in: overlay rfkill crc32_ce crct10dif_ce fuse
[   47.761335] Process execveat03 (pid: 2880, stack limit = 0xffff00000ec60000)
[   47.768397] CPU: 3 PID: 2880 Comm: execveat03 Not tainted
4.14.186-rc1-00111-gb518002db397 #1
[   47.776933] Hardware name: ARM Juno development board (r2) (DT)
[   47.782860] task: ffff8009546ade80 task.stack: ffff00000ec60000
[   47.788819] pc : ovl_path_open+0xa8/0xb0 [overlay]
[   47.793641] lr : ovl_check_d_type_supported+0x38/0xf0 [overlay]
[   47.799567] sp : ffff00000ec63ba0 pstate : 40000145
[   47.804449] x29: ffff00000ec63ba0 x28: 0000000000000000
[   47.809770] x27: ffff800955bfb710 x26: ffff800955bfb700
[   47.815091] x25: ffff00000ec63ce0 x24: 0000000000000000
[   47.820412] x23: ffff00000ec63cd0 x22: 0000000000000001
[   47.825733] x21: ffff8009509609b8 x20: ffff00000ec63ce0
[   47.831054] x19: 0000000000004000 x18: 0000000000000000
[   47.836375] x17: 0000000000000000 x16: ffff0000080d1800
[   47.841696] x15: 095a041701101c00 x14: ff00000000000000
[   47.847017] x13: 0000000000000000 x12: 000000000000000b
[   47.852338] x11: 0101010101010101 x10: ffff800950960b40
[   47.857659] x9 : 7f7f7f7f7f7f7f7f x8 : 6f2d6c6473727872
[   47.862980] x7 : 001c100117045a09 x6 : 095a041701101c00
[   47.868301] x5 : 0000000000000000 x4 : 0000000000000000
[   47.873622] x3 : 0000000000000000 x2 : ffff000000b7ec88
[   47.878943] x1 : ffff800953f78180 x0 : 0000000000004000
[   47.884264] Call trace:
[   47.886736]  ovl_path_open+0xa8/0xb0 [overlay]
[   47.891209]  ovl_check_d_type_supported+0x38/0xf0 [overlay]
[   47.896812]  ovl_fill_super+0x540/0xc98 [overlay]
[   47.901528]  mount_nodev+0x4c/0xa8
[   47.904954]  ovl_mount+0x14/0x28 [overlay]
[   47.909056]  mount_fs+0x54/0x188
[   47.912289]  vfs_kern_mount.part.0+0x4c/0x118
[   47.916651]  do_mount+0x1cc/0xbe0
[   47.919970]  compat_SyS_mount+0xb0/0x1b8
[   47.923899]  __sys_trace_return+0x0/0x4
[   47.927742] Code: f94013f5 a8c37bfd d65f03c0 d4210000 (d4210000)
[   47.933845] ---[ end trace 1b32b515dde8d9db ]---

Test link,
https://lkft.validation.linaro.org/scheduler/job/1517781#L1266

metadata:
  git branch: linux-4.14.y
  git repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
  git commit: b518002db397b51173a3e17045bfb3ff0e1aa0ed
  kernel-config:
https://builds.tuxbuild.com/B_xCv6-0v8npcEVw6hA_ZQ/kernel.config


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