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[PATCH 3.2 43/94] fix d_walk()/non-delayed __d_free() race

From Ben Hutchings <ben@decadent.org.uk>
Newsgroups linux.kernel
Subject [PATCH 3.2 43/94] fix d_walk()/non-delayed __d_free() race
Date 2016-08-14 14:00 +0200
Message-ID <s62f9-7AQ-59@gated-at.bofh.it> (permalink)
References <s5LnX-4sk-7@gated-at.bofh.it>
Organization linux.* mail to news gateway

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3.2.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@zeniv.linux.org.uk>

commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream.

Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay.  Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.

Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover.  Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.2:
 - Adjust context
 - Also set the flag in __d_materialise_dentry())]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/dcache.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1261,7 +1261,7 @@ struct dentry *d_alloc(struct dentry * p
 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
 	if (!dentry)
 		return NULL;
-
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	spin_lock(&parent->d_lock);
 	/*
 	 * don't need child lock because it is not subject
@@ -2011,7 +2011,6 @@ static void __d_rehash(struct dentry * e
 {
 	BUG_ON(!d_unhashed(entry));
 	hlist_bl_lock(b);
-	entry->d_flags |= DCACHE_RCUACCESS;
 	hlist_bl_add_head_rcu(&entry->d_hash, b);
 	hlist_bl_unlock(b);
 }
@@ -2195,6 +2194,7 @@ static void __d_move(struct dentry * den
 
 	/* ... and switch the parents */
 	if (IS_ROOT(dentry)) {
+		dentry->d_flags |= DCACHE_RCUACCESS;
 		dentry->d_parent = target->d_parent;
 		target->d_parent = target;
 		INIT_LIST_HEAD(&target->d_child);
@@ -2311,6 +2311,7 @@ static void __d_materialise_dentry(struc
 	switch_names(dentry, anon);
 	swap(dentry->d_name.hash, anon->d_name.hash);
 
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	dentry->d_parent = (aparent == anon) ? dentry : aparent;
 	list_del(&dentry->d_child);
 	if (!IS_ROOT(dentry))

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[PATCH 3.2 00/94] 3.2.82-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 26/94] fs/cifs: correctly to anonymous authentication  for the LANMAN authentication Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 23/94] x86/PCI: Mark Broadwell-EP Home Agent 1 as  having non-compliant BARs Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 93/94] tcp: make challenge acks less predictable Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 62/94] UBIFS: Implement ->migratepage() Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 42/94] x86, build: copy ldlinux.c32 to image.iso Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 54/94] kvm: Fix irq route entries exceeding  KVM_MAX_IRQ_ROUTES Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 13/94] USB: serial: option: add even more ZTE device ids Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 35/94] Input: xpad - prevent spurious input from wired  Xbox 360 controllers Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 43/94] fix d_walk()/non-delayed __d_free() race Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 18/94] powerpc/mm/hash64: Factor out hash preload  psize check Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 86/94] proc: prevent stacking filesystems on top Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 34/94] RDMA/cxgb3: device driver frees DMA memory with  different size Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 22/94] net/mlx4_core: Fix access to uninitialized index Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 82/94] xenbus: don't BUG() on user mode induced condition Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 69/94] ALSA: dummy: Fix a use-after-free at closing Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 74/94] NFS: Fix another OPEN_DOWNGRADE bug Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 73/94] ALSA: echoaudio: Fix memory allocation Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 61/94] mm: Export migrate_page_move_mapping and  migrate_page_copy Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 02/94] ath5k: Change led pin configuration for compaq  c700 laptop Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  Re: [PATCH 3.2 00/94] 3.2.82-rc1 review Guenter Roeck <linux@roeck-us.net> - 2016-08-14 17:10 +0200
  [PATCH 3.2 39/94] ARM: fix PTRACE_SETVFPREGS on SMP systems Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 85/94] fs: limit filesystem stacking depth Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 11/94] tty: vt, return error when con_startup fails Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 91/94] tipc: fix an infoleak in tipc_nl_compat_link_dump Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 15/94] MIPS: Adjust set_pte() SMP fix to handle  R10000_LLSC_WAR Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 60/94] ubi: Make recover_peb power cut aware Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 03/94] crypto: s5p-sss - Fix missed interrupts when  working with 8 kB blocks Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 64/94] xen/pciback: Fix conf_space read/write overlap  check. Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 25/94] fs/cifs: correctly to anonymous authentication  via NTLMSSP Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 37/94] Input: pwm-beeper - fix - scheduling while atomic Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 21/94] mmc: mmc: Fix partition switch timeout for some  eMMCs Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 88/94] ALSA: timer: Fix leak in SNDRV_TIMER_IOCTL_PARAMS Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 01/94] regmap: cache: Fix typo in cache_bypass  parameter description Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 63/94] can: fix oops caused by wrong rtnl dellink usage Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 77/94] x86/amd_nb: Fix boot crash on non-AMD systems Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 79/94] bonding: prevent out of bound accesses Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 06/94] crypto: s5p-sss - fix incorrect usage of  scatterlists api Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 59/94] can: at91_can: RX queue could get stuck at high  bus load Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 70/94] fs/nilfs2: fix potential underflow in call to  crc32_le Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 71/94] staging: iio: accel: fix error check Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 84/94] cifs: dynamic allocation of ntlmssp blob Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 52/94] kernel/sysrq, watchdog, sched/core: Reset  watchdog on all CPUs while processing sysrq-w Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 40/94] KVM: x86: fix OOPS after invalid KVM_SET_DEBUGREGS Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 53/94] base: make module_create_drivers_dir race-free Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 87/94] USB: usbfs: fix potential infoleak in devio Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 48/94] staging:iio: trigger fixes for repeat request  of same trigger and allocation failure Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 09/94] ext4: fix hang when processing corrupted  orphaned inode list Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 75/94] batman-adv: Fix use-after-free/double-free of  tt_req_node Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200

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