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From:   Liangyan <liangyan.peng@linux.alibaba.com>
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
        linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        joseph.qi@linux.alibaba.com, liangyan.peng@linux.alibaba.com
Subject: [PATCH v3] ovl: fix  dentry leak in ovl_get_redirect
Date:   Tue, 22 Dec 2020 02:33:27 +0800
Message-Id: <20201221183327.134077-1-liangyan.peng@linux.alibaba.com>
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Precedence: bulk

We need to lock d_parent->d_lock before dget_dlock, or this may
have d_lockref updated parallelly like calltrace below which will
cause dentry->d_lockref leak and risk a crash.

     CPU 0                                CPU 1
ovl_set_redirect                       lookup_fast
  ovl_get_redirect                       __d_lookup
    dget_dlock
      //no lock protection here            spin_lock(&dentry->d_lock)
      dentry->d_lockref.count++            dentry->d_lockref.count++

[   49.799059] PGD 800000061fed7067 P4D 800000061fed7067 PUD 61fec5067 PMD 0
[   49.799689] Oops: 0002 [#1] SMP PTI
[   49.800019] CPU: 2 PID: 2332 Comm: node Not tainted 4.19.24-7.20.al7.x86_64 #1
[   49.800678] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 8a46cfe 04/01/2014
[   49.801380] RIP: 0010:_raw_spin_lock+0xc/0x20
[   49.803470] RSP: 0018:ffffac6fc5417e98 EFLAGS: 00010246
[   49.803949] RAX: 0000000000000000 RBX: ffff93b8da3446c0 RCX: 0000000a00000000
[   49.804600] RDX: 0000000000000001 RSI: 000000000000000a RDI: 0000000000000088
[   49.805252] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff993cf040
[   49.805898] R10: ffff93b92292e580 R11: ffffd27f188a4b80 R12: 0000000000000000
[   49.806548] R13: 00000000ffffff9c R14: 00000000fffffffe R15: ffff93b8da3446c0
[   49.807200] FS:  00007ffbedffb700(0000) GS:ffff93b927880000(0000) knlGS:0000000000000000
[   49.807935] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   49.808461] CR2: 0000000000000088 CR3: 00000005e3f74006 CR4: 00000000003606a0
[   49.809113] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   49.809758] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   49.810410] Call Trace:
[   49.810653]  d_delete+0x2c/0xb0
[   49.810951]  vfs_rmdir+0xfd/0x120
[   49.811264]  do_rmdir+0x14f/0x1a0
[   49.811573]  do_syscall_64+0x5b/0x190
[   49.811917]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   49.812385] RIP: 0033:0x7ffbf505ffd7
[   49.814404] RSP: 002b:00007ffbedffada8 EFLAGS: 00000297 ORIG_RAX: 0000000000000054
[   49.815098] RAX: ffffffffffffffda RBX: 00007ffbedffb640 RCX: 00007ffbf505ffd7
[   49.815744] RDX: 0000000004449700 RSI: 0000000000000000 RDI: 0000000006c8cd50
[   49.816394] RBP: 00007ffbedffaea0 R08: 0000000000000000 R09: 0000000000017d0b
[   49.817038] R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000000012
[   49.817687] R13: 00000000072823d8 R14: 00007ffbedffb700 R15: 00000000072823d8
[   49.818338] Modules linked in: pvpanic cirrusfb button qemu_fw_cfg atkbd libps2 i8042
[   49.819052] CR2: 0000000000000088
[   49.819368] ---[ end trace 4e652b8aa299aa2d ]---
[   49.819796] RIP: 0010:_raw_spin_lock+0xc/0x20
[   49.821880] RSP: 0018:ffffac6fc5417e98 EFLAGS: 00010246
[   49.822363] RAX: 0000000000000000 RBX: ffff93b8da3446c0 RCX: 0000000a00000000
[   49.823008] RDX: 0000000000000001 RSI: 000000000000000a RDI: 0000000000000088
[   49.823658] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff993cf040
[   49.825404] R10: ffff93b92292e580 R11: ffffd27f188a4b80 R12: 0000000000000000
[   49.827147] R13: 00000000ffffff9c R14: 00000000fffffffe R15: ffff93b8da3446c0
[   49.828890] FS:  00007ffbedffb700(0000) GS:ffff93b927880000(0000) knlGS:0000000000000000
[   49.830725] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   49.832359] CR2: 0000000000000088 CR3: 00000005e3f74006 CR4: 00000000003606a0
[   49.834085] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   49.835792] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Fixes: a6c606551141 ("ovl: redirect on rename-dir")
Signed-off-by: Liangyan <liangyan.peng@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/overlayfs/dir.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 28a075b5f5b2..e9aa4a12ad82 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -973,6 +973,7 @@ static char *ovl_get_redirect(struct dentry *dentry, bool abs_redirect)
 	for (d = dget(dentry); !IS_ROOT(d);) {
 		const char *name;
 		int thislen;
+		struct dentry *parent = NULL;
 
 		spin_lock(&d->d_lock);
 		name = ovl_dentry_get_redirect(d);
@@ -992,11 +993,10 @@ static char *ovl_get_redirect(struct dentry *dentry, bool abs_redirect)
 
 		buflen -= thislen;
 		memcpy(&buf[buflen], name, thislen);
-		tmp = dget_dlock(d->d_parent);
 		spin_unlock(&d->d_lock);
-
+		parent = dget_parent(d);
 		dput(d);
-		d = tmp;
+		d = parent;
 
 		/* Absolute redirect: finished */
 		if (buf[buflen] == '/')
-- 
2.14.4.44.g2045bb6