Re: [PATCH v2] ovl: fix NULL ref while cleanup index when mount with nfs_export

[Murphy Zhou <jencce.kernel@gmail.com>]

On Sat, Jun 20, 2020 at 07:14:02PM +0300, Amir Goldstein wrote:
> On Sat, Jun 20, 2020 at 4:28 PM Murphy Zhou <jencce.kernel@gmail.com> wrote:
> >
> > Mounting with nfs_export=on, xfstests overlay/031 triggers panic
> > since v5.8-rc1 overlayfs updates.
> >
> > [ 7492.110430] run fstests overlay/031 at 2020-06-10 00:25:16
> > [ 7492.487300] overlayfs: disabling metacopy due to nfs_export=on
> > [ 7492.514270] overlayfs: "xino=on" is useless with all layers on same fs, ignore.
> > [ 7492.648049] overlayfs: disabling metacopy due to nfs_export=on
> > [ 7492.675189] overlayfs: "xino=on" is useless with all layers on same fs, ignore.
> > [ 7492.781437] overlayfs: disabling metacopy due to nfs_export=on
> > [ 7492.808608] overlayfs: "xino=on" is useless with all layers on same fs, ignore.
> > [ 7492.842132] overlayfs: orphan index entry (index/00fb1d000175e1f1e51e134b75b98d1f572f21252d030004002ae1559a, ftype=4000, nlink=2)
> > [ 7492.895298] BUG: kernel NULL pointer dereference, address: 0000000000000030
> > [ 7492.926984] #PF: supervisor read access in kernel mode
> > [ 7492.950703] #PF: error_code(0x0000) - not-present page
> > [ 7492.974243] PGD 0 P4D 0
> > [ 7492.985754] Oops: 0000 [#1] SMP PTI
> > [ 7493.001771] CPU: 11 PID: 951781 Comm: mount Not tainted 5.7.0+ #1
> > [ 7493.029799] Hardware name: HP ProLiant DL388p Gen8, BIOS P70 09/18/2013
> > [ 7493.059809] RIP: 0010:ovl_cleanup_and_whiteout+0x28/0x220 [overlay]
> > [ 7493.087978] Code: 00 00 0f 1f 44 00 00 41 57 41 56 49 89 f6 41 55 41 54 49 89 d4 55 48 89 fd 53 48 83 ec 08 4c 8b 47 20 48 83 bf a8 00 00 00 00 <4d> 8b 68 30 0f 84 41 01 00 00 80 7d 7c 00 0f 85 b7 00 00 00 48 8b
> > [ 7493.173542] RSP: 0018:ffffbb8409a7fc20 EFLAGS: 00010246
> > [ 7493.197332] RAX: 00000000fffffffe RBX: ffff9425aa44ee40 RCX: 0000000000000000
> > [ 7493.230058] RDX: ffff9420f64c5a40 RSI: ffff9425a25d91c8 RDI: ffff94259dfc9680
> > [ 7493.262699] RBP: ffff94259dfc9680 R08: 0000000000000000 R09: 000000000000000b
> > [ 7493.295568] R10: 0000000000000000 R11: ffffbb8409a7fab8 R12: ffff9420f64c5a40
> > [ 7493.328117] R13: ffff94259dfc9680 R14: ffff9425a25d91c8 R15: ffff9420f64c5a40
> > [ 7493.360681] FS:  00007f43bdfc2080(0000) GS:ffff9425af740000(0000) knlGS:0000000000000000
> > [ 7493.397797] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 7493.424340] CR2: 0000000000000030 CR3: 000000082bd18001 CR4: 00000000001606e0
> > [ 7493.456765] Call Trace:
> > [ 7493.467695]  ovl_indexdir_cleanup+0x1ab/0x330 [overlay]
> > [ 7493.491605]  ? ovl_cache_entry_find_link.constprop.18+0x80/0x80 [overlay]
> > [ 7493.522754]  ovl_fill_super+0x1031/0x11d0 [overlay]
> > [ 7493.545183]  ? sget+0x1c7/0x220
> > [ 7493.559242]  ? get_anon_bdev+0x40/0x40
> > [ 7493.576593]  ? ovl_show_options+0x230/0x230 [overlay]
> > [ 7493.599407]  mount_nodev+0x48/0xa0
> > [ 7493.615187]  legacy_get_tree+0x27/0x40
> > [ 7493.632193]  vfs_get_tree+0x25/0xb0
> > [ 7493.647926]  do_mount+0x7ae/0x9d0
> > [ 7493.662996]  ? _copy_from_user+0x2c/0x60
> > [ 7493.681534]  __x64_sys_mount+0xc4/0xe0
> > [ 7493.698370]  do_syscall_64+0x55/0x1b0
> > [ 7493.715177]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [ 7493.737697] RIP: 0033:0x7f43bcffec8e
> > [ 7493.753986] Code: Bad RIP value.
> > [ 7493.768721] RSP: 002b:00007ffe1b7c74f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> > [ 7493.803468] RAX: ffffffffffffffda RBX: 000055ba081c1310 RCX: 00007f43bcffec8e
> > [ 7493.837362] RDX: 000055ba081c1a00 RSI: 000055ba081c1a40 RDI: 000055ba081c1a20
> > [ 7493.872745] RBP: 00007f43bdda9184 R08: 000055ba081c1880 R09: 0000000000000003
> > [ 7493.905227] R10: 00000000c0ed0000 R11: 0000000000000246 R12: 0000000000000000
> > [ 7493.938152] R13: 00000000c0ed0000 R14: 000055ba081c1a20 R15: 000055ba081c1a00
> >
> > Bisect says the first bad commit is:
> >     [c21c839b8448dd4b1e37ffc1bde928f57d34c0db] ovl: whiteout inode sharing
> >
> > Minimal reproducer:
> > --------------------------------------------------
> > rm -rf l u w m
> > mkdir -p l u w m
> > mkdir -p l/testdir
> > touch l/testdir/testfile
> > mount -t overlay -o lowerdir=l,upperdir=u,workdir=w,nfs_export=on overlay m
> > echo 1 > m/testdir/testfile
> > umount m
> > rm -rf u/testdir
> > mount -t overlay -o lowerdir=l,upperdir=u,workdir=w,nfs_export=on overlay m
> > umount m
> > --------------------------------------------------
> >
> > When mount with nfs_export=on, and fail to verify an orphan index, we're
> > cleaning this index from indexdir by calling ovl_cleanup_and_whiteout,
> > in which we should clean indexdir rather than workdir. We start to use
> > ofs structure and only clean workdir since commit c21c839b8448
> > ("ovl: whiteout inode sharing"), breaking the nfs_export code path.
> >
> > Fixing this by passing additional explicit workdir argument to the cleanup
> > helper and passing indexdir as workdir argument in ovl_indexdir_cleanup and
> > ovl_cleanup_index.
> >
> > Suggested-by: Amir Goldstein <amir73il@gmail.com>
> > Signed-off-by: Murphy Zhou <jencce.kernel@gmail.com>
> > ---
> > v2:
> >     Pass workdir as argument along with ofs to the helper instead of
> > checking availability of the dirs.
> >     Pass indexdir in ovl_indexdir_cleanup and ovl_cleanup_index.
> 
> Sorry for not looking closer before, I wasn't near my workstation.
> Here is another suggestion.
> I think Miklos will like this one better, because he was the one who removed
> the workdir from Chengguang's original patch.
> 
> The design was that ovl->workdir will point at ovl->indexdir, but we did
> it too late for ovl_indexdir_cleanup().
> No reason not to do it sooner, because once we get success from
> ofs->indexdir = ovl_workdir_create(... there is no turning back.
> 
> Feel free to re-post this with proper commit message after testing and
> verifying that moving the code didn't break any other error path.
> 
> Thanks,
> Amir.

> From 4e04457a1b616cc84331214017014bebd479461a Mon Sep 17 00:00:00 2001
> From: Amir Goldstein <amir73il@gmail.com>
> Date: Sat, 20 Jun 2020 19:04:35 +0300
> Subject: [PATCH] ovl: fix NULL ref while cleanup index when mount with
>  nfs_export

Test result looks good to go.

Thanks for the fix!
> 
> ...
> 
> Fixes: commit c21c839b8448 ("ovl: whiteout inode sharing")
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/overlayfs/super.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 91476bc422f9..15939ab39c1c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1354,6 +1354,12 @@ static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
>  
>  	ofs->indexdir = ovl_workdir_create(ofs, OVL_INDEXDIR_NAME, true);
>  	if (ofs->indexdir) {
> +		/* index dir will act also as workdir */
> +		iput(ofs->workdir_trap);
> +		ofs->workdir_trap = NULL;
> +		dput(ofs->workdir);
> +		ofs->workdir = dget(ofs->indexdir);
> +
>  		err = ovl_setup_trap(sb, ofs->indexdir, &ofs->indexdir_trap,
>  				     "indexdir");
>  		if (err)
> @@ -1843,20 +1849,12 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
>  		sb->s_flags |= SB_RDONLY;
>  
>  	if (!(ovl_force_readonly(ofs)) && ofs->config.index) {
> -		/* index dir will act also as workdir */
> -		dput(ofs->workdir);
> -		ofs->workdir = NULL;
> -		iput(ofs->workdir_trap);
> -		ofs->workdir_trap = NULL;
> -
>  		err = ovl_get_indexdir(sb, ofs, oe, &upperpath);
>  		if (err)
>  			goto out_free_oe;
>  
>  		/* Force r/o mount with no index dir */
> -		if (ofs->indexdir)
> -			ofs->workdir = dget(ofs->indexdir);
> -		else
> +		if (!ofs->indexdir)
>  			sb->s_flags |= SB_RDONLY;
>  	}
>  
> -- 
> 2.17.1
> 


-- 
Murphy