Re: [PATCH AUTOSEL 4.19 138/172] ovl: verify permissions in ovl_path_open()

Naresh Kamboju
2020-06-23T15:35:53Z

On Thu, 18 Jun 2020 at 07:16, Sasha Levin <sashal@kernel.org> wrote:
>
> From: Miklos Szeredi <mszeredi@redhat.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@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.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