Re: [PATCH AUTOSEL 5.7 319/388] ovl: verify permissions in ovl_path_open()

Naresh Kamboju
2020-06-23T15:30:18Z

On Thu, 18 Jun 2020 at 08:03, 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 36b60788ee47..a0878039332a 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -459,7 +459,32 @@ 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

[ 564.915016] ------------[ cut here ]------------
[ 564.919654] kernel BUG at fs/overlayfs/util.c:466!
[ 564.924458] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 564.929954] Modules linked in: overlay rfkill tda998x cec
drm_kms_helper drm crct10dif_ce fuse
[ 564.938617] CPU: 1 PID: 15054 Comm: execveat03 Not tainted
5.7.6-rc1-00793-gccc085714c08 #1
[ 564.946987] Hardware name: ARM Juno development board (r2) (DT)
[ 564.952921] pstate: 60000005 (nZCv daif -PAN -UAO)
[ 564.957786] pc : ovl_path_open+0xd0/0xd8 [overlay]
[ 564.962642] lr : ovl_path_open+0x30/0xd8 [overlay]
[ 564.967443] sp : ffff00090a65f740
[ 564.970763] x29: ffff00090a65f740 x28: 0000000000000000
[ 564.976091] x27: ffff00090a65f950 x26: ffffa000097506c0
[ 564.981419] x25: ffff00090388f000 x24: ffff000912b39a28
[ 564.986746] x23: ffff00090a65f950 x22: ffff00090b45e580
[ 564.992072] x21: ffff00090a65f950 x20: ffff0008dddbcb10
[ 564.997398] x19: 0000000000004000 x18: 0000000000000000
[ 565.002723] x17: 0000000000000000 x16: 0000000000000000
[ 565.008048] x15: 0000000000000000 x14: ffffa000103c0898
[ 565.013374] x13: ffffa00010382fec x12: ffff80011bd530dc
[ 565.018700] x11: 1fffe0011bd530db x10: ffff80011bd530db
[ 565.024026] x9 : dfffa00000000000 x8 : ffff0008dea986d8
[ 565.029351] x7 : 0000000000000001 x6 : 00000000f1f1f1f1
[ 565.034677] x5 : 00000000f3000000 x4 : dfffa00000000000
[ 565.040003] x3 : ffffa0000973f950 x2 : 0000000000000007
[ 565.045328] x1 : 0000000000004000 x0 : ffff00090f79c930
[ 565.050653] Call trace:
[ 565.053162] ovl_path_open+0xd0/0xd8 [overlay]
[ 565.057670] ovl_check_d_type_supported+0x9c/0x180 [overlay]
[ 565.063396] ovl_get_workdir.isra.0+0x238/0x5e0 [overlay]
[ 565.068861] ovl_fill_super+0x800/0x1a48 [overlay]
[ 565.073673] mount_nodev+0x50/0xc0
[ 565.077135] ovl_mount+0x1c/0x28 [overlay]
[ 565.081245] legacy_get_tree+0x74/0xc0
[ 565.085005] vfs_get_tree+0x4c/0x160
[ 565.088589] do_mount+0x700/0xb90
[ 565.091913] __arm64_sys_mount+0xc0/0x110
[ 565.095938] el0_svc_common.constprop.0+0xa4/0x1e0
[ 565.100742] do_el0_svc+0x38/0xa0
[ 565.104068] el0_sync_handler+0x11c/0x190
[ 565.108087] el0_sync+0x158/0x180
[ 565.111419] Code: a8c37bfd d50323bf d65f03c0 d4210000 (d4210000)
[ 565.117529] ---[ end trace 357a3872beec6c53 ]---
[ 565.122157] note: execveat03[15054] exited with preempt_count 1
[ 565.129476] ------------[ cut here ]------------
[ 565.134122] WARNING: CPU: 1 PID: 0 at kernel/rcu/tree.c:569
rcu_idle_enter+0xd0/0xd8
[ 565.141879] Modules linked in: overlay rfkill tda998x cec
drm_kms_helper drm crct10dif_ce fuse
[ 565.150539] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G D
5.7.6-rc1-00793-gccc085714c08 #1
[ 565.159866] Hardware name: ARM Juno development board (r2) (DT)
[ 565.165799] pstate: 200003c5 (nzCv DAIF -PAN -UAO)
[ 565.170603] pc : rcu_idle_enter+0xd0/0xd8
[ 565.174623] lr : rcu_idle_enter+0x34/0xd8
[ 565.178639] sp : ffff000935577ea0
[ 565.181958] x29: ffff000935577ea0 x28: 0000000000000000
[ 565.187285] x27: ffff000912d83000 x26: ffffa0001359e2c0
[ 565.192611] x25: ffff000935552b80 x24: 1fffe00126aaefe6
[ 565.198098] x23: ffffa000125abff8 x22: ffffa0001359e298
[ 565.203424] x21: ffff000936606fd0 x20: ffffa000125b5f00
[ 565.208909] x19: ffff000936606f00 x18: 0000000000000000
Broadcast message from systemd-jo[ 565.214234] x17: 0000000000000000
x16: 0000000000000000
urnald@juno (Mon 2020-06-22 19:5[ 565.222417] x15: 0000000000000000
x14: ffffa000103c1370
9:27 UTC):
[ 565.230517] x13: ffffa000103c0898 x12: ffff800126cc0d8c
[ 565.236959] x11: 1fffe00126cc0d8b x10: ffff800126cc0d8b
[ 565.242285] x9 : dfffa00000000000 x8 : ffff000936606c5b
[ 565.247683] x7 : 0000000000000001 x6 : ffff000936606c58
[ 565.253009] x5 : 00007ffed933f275 x4 : dfffa00000000000
[ 565.258493] x3 : ffffa000101d48e4 x2 : 0000000000000007
kernel[300]: [ 564.924458] Inter[ 565.263819] x1 : 4000000000000002
x0 : 4000000000000000
nal error: Oops - BUG: 0 [#1] PR[ 565.272001] Call trace:
EEMPT SMP
[ 565.277235] rcu_idle_enter+0xd0/0xd8
[ 565.281938] do_idle+0x288/0x328
[ 565.285176] cpu_startup_entry+0x28/0x48
[ 565.289182] secondary_start_kernel+0x248/0x2b0
[ 565.293721] ---[ end trace 357a3872beec6c54 ]---

https://lkft.validation.linaro.org/scheduler/job/1515478#L3876

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Linaro LKFT