[PATCH 3.13.y-ckt 63/86] Btrfs: fix race when listing an inode's xattrs

From	Kamal Mostafa <kamal@canonical.com>
Newsgroups	linux.kernel
Subject	[PATCH 3.13.y-ckt 63/86] Btrfs: fix race when listing an inode's xattrs
Date	2015-12-03 00:10 +0100
Message-ID	<qBoH8-5jn-29@gated-at.bofh.it> (permalink)
References	<qBoxr-50H-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

3.13.11-ckt31 -stable review patch.  If anyone has any objections, please let me know.

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

From: Filipe Manana <fdmanana@suse.com>

commit f1cd1f0b7d1b5d4aaa5711e8f4e4898b0045cb6d upstream.

When listing a inode's xattrs we have a time window where we race against
a concurrent operation for adding a new hard link for our inode that makes
us not return any xattr to user space. In order for this to happen, the
first xattr of our inode needs to be at slot 0 of a leaf and the previous
leaf must still have room for an inode ref (or extref) item, and this can
happen because an inode's listxattrs callback does not lock the inode's
i_mutex (nor does the VFS does it for us), but adding a hard link to an
inode makes the VFS lock the inode's i_mutex before calling the inode's
link callback.

If we have the following leafs:

               Leaf X (has N items)                    Leaf Y

 [ ... (257 INODE_ITEM 0) (257 INODE_REF 256) ]  [ (257 XATTR_ITEM 12345), ... ]
           slot N - 2         slot N - 1              slot 0

The race illustrated by the following sequence diagram is possible:

       CPU 1                                               CPU 2

  btrfs_listxattr()

    searches for key (257 XATTR_ITEM 0)

    gets path with path->nodes[0] == leaf X
    and path->slots[0] == N

    because path->slots[0] is >=
    btrfs_header_nritems(leaf X), it calls
    btrfs_next_leaf()

    btrfs_next_leaf()
      releases the path

                                                   adds key (257 INODE_REF 666)
                                                   to the end of leaf X (slot N),
                                                   and leaf X now has N + 1 items

      searches for the key (257 INODE_REF 256),
      with path->keep_locks == 1, because that
      is the last key it saw in leaf X before
      releasing the path

      ends up at leaf X again and it verifies
      that the key (257 INODE_REF 256) is no
      longer the last key in leaf X, so it
      returns with path->nodes[0] == leaf X
      and path->slots[0] == N, pointing to
      the new item with key (257 INODE_REF 666)

    btrfs_listxattr's loop iteration sees that
    the type of the key pointed by the path is
    different from the type BTRFS_XATTR_ITEM_KEY
    and so it breaks the loop and stops looking
    for more xattr items
      --> the application doesn't get any xattr
          listed for our inode

So fix this by breaking the loop only if the key's type is greater than
BTRFS_XATTR_ITEM_KEY and skip the current key if its type is smaller.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
[ luis: backported to 3.16:
  - drop btrfs_key_type(), which was dropped upstream by
    962a298f3511 ("btrfs: kill the key type accessor helpers") ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 fs/btrfs/xattr.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 42c6b2c..0e10de6 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -307,8 +307,10 @@ ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
 		/* check to make sure this item is what we want */
 		if (found_key.objectid != key.objectid)
 			break;
-		if (btrfs_key_type(&found_key) != BTRFS_XATTR_ITEM_KEY)
+		if (found_key.type > BTRFS_XATTR_ITEM_KEY)
 			break;
+		if (found_key.type < BTRFS_XATTR_ITEM_KEY)
+			goto next;
 
 		di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
 		if (verify_dir_item(root, leaf, di))
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Thread

[3.13.y-ckt stable] Linux 3.13.11-ckt31 stable review Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 04/86] drm/radeon: add quirk for ASUS R7 370 Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 54/86] ALSA: hda - Add Intel Lewisburg device IDs Audio Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 84/86] drm: Fix return value of drm_framebuffer_init() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 74/86] mwifiex: fix mwifiex_rdeeprom_read() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 82/86] packet: fix match_fanout_group() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 61/86] perf: Fix inherited events vs. tracepoint filters Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 76/86] devres: fix a for loop bounds check Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 64/86] storvsc: Don't set the SRB_FLAGS_QUEUE_ACTION_ENABLE flag Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 86/86] TPM: Avoid reference to potentially freed memory Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 14/86] [3.13-stable only] fib_rules: Fix dump_rules() not to exit early Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:00 +0100
  [PATCH 3.13.y-ckt 71/86] FS-Cache: Handle a write to the page immediately beyond the EOF marker Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 47/86] xtensa: fixes for configs without loop option Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 55/86] firewire: ohci: fix JMicron JMB38x IT context discovery Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 79/86] perf trace: Fix documentation for -i Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 60/86] Btrfs: fix race leading to BUG_ON when running delalloc for nodatacow Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 73/86] wm831x_power: Use IRQF_ONESHOT to request threaded IRQs Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 69/86] FS-Cache: Increase reference of parent after registering, netfs success Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 59/86] Btrfs: fix race leading to incorrect item deletion when dropping extents Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 63/86] Btrfs: fix race when listing an inode's xattrs Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 65/86] KVM: x86: Defining missing x86 vectors Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 78/86] ipv6: fix tunnel error handling Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 56/86] proc: actually make proc_fd_permission() thread-friendly Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 66/86] KVM: x86: work around infinite loop in microcode when #AC is delivered Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 57/86] printk: prevent userland from spoofing kernel messages Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 68/86] drm/ast: Initialized data needed to map fbdev memory Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 70/86] FS-Cache: Don't override netfs's primary_index if registering failed Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 81/86] mac80211: fix driver RSSI event calculations Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 62/86] scsi_sysfs: Fix queue_ramp_up_period return code Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 80/86] bonding: fix panic on non-ARPHRD_ETHER enslave failure Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 72/86] binfmt_elf: Don't clobber passed executable's file header Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 58/86] x86/cpu: Call verify_cpu() after having entered long mode too Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:10 +0100
  [PATCH 3.13.y-ckt 50/86] recordmcount: Fix endianness handling bug for nop_mcount Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 46/86] crypto: algif_hash - Only export and import on sockets with data Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 49/86] mac80211: allow null chandef in tracing Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 34/86] Bluetooth: ath3k: Add support of AR3012 0cf3:817b device Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 40/86] MAINTAINERS: Add public mailing list for ARC Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 38/86] ALSA: hda/realtek - Dell XPS one ALC3260 speaker no sound after resume back Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 44/86] mtd: blkdevs: fix potential deadlock + lockdep warnings Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 12/86] net: avoid NULL deref in inet_ctl_sock_destroy() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 39/86] ALSA: hda - Disable 64bit address for Creative HDA controllers Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 17/86] net: mvneta: Fix CPU_MAP registers initialisation Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 35/86] spi: atmel: Fix DMA-setup for transfers with more than 8 bits per word Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 43/86] can: Use correct type in sizeof() in nla_put() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 45/86] Revert "dm mpath: fix stalls when handling invalid ioctls" Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 32/86] Bluetooth: hidp: fix device disconnect on idle timeout Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 41/86] megaraid_sas: Do not use PAGE_SIZE for max_sectors Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 36/86] staging: rtl8712: Add device ID for Sitecom WLA2100 Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 31/86] [media] media: vb2 dma-contig: Fully cache synchronise buffers in prepare and finish Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 42/86] arm64: Fix compat register mappings Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 18/86] mtd: mtdpart: fix add_mtd_partitions error path Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 37/86] ACPI: Use correct IRQ when uninstalling ACPI interrupt handler Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 48/86] megaraid_sas : SMAP restriction--do not access user memory from IOCTL code Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 11/86] qmi_wwan: fix entry for HP lt4112 LTE/HSPA+ Gobi 4G Module Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 53/86] ALSA: hda - Apply pin fixup for HP ProBook 6550b Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 51/86] KVM: Disable SMAP for guests in EPT realmode and EPT unpaging mode Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 52/86] KVM: VMX: fix SMEP and SMAP without EPT Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 13/86] net: fix a race in dst_release() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:20 +0100
  [PATCH 3.13.y-ckt 06/86] irda: precedence bug in irlmp_seq_hb_idx() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 08/86] RDS-TCP: Recover correctly from pskb_pull()/pksb_trim() failure in rds_tcp_data_recv Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 16/86] [media] v4l2-compat-ioctl32: fix alignment for ARM64 Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 33/86] Bluetooth: ath3k: Add new AR3012 0930:021c id Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 02/86] x86/setup: Fix low identity map for >= 2GB kernel range Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 20/86] ARM: 8426/1: dma-mapping: add missing range check in dma_mmap() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 29/86] ext4, jbd2: ensure entering into panic after recording an error in superblock Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 25/86] iommu/vt-d: Fix error in detect ATS capability Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 05/86] drm/radeon: fix quirk for MSI R7 370 Armor 2X Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 22/86] spi: ti-qspi: Fix data corruption seen on r/w stress test Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 28/86] [PATCH] fix calculation of meta_bg descriptor backups Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 10/86] ipmr: fix possible race resulting from improper usage of IP_INC_STATS_BH() in preemptible context. Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 23/86] lockd: create NSM handles per net namespace Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 07/86] macvtap: unbreak receiving of gro skb with frag list Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 15/86] HID: core: Avoid uninitialized buffer access Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 01/86] x86/setup: Extend low identity map to cover whole kernel range Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 03/86] drm/radeon: add quirk for MSI R7 370 Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 09/86] stmmac: Correctly report PTP capabilities. Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 24/86] ARM: common: edma: Fix channel parameter for irq callbacks Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 21/86] ARM: 8427/1: dma-mapping: add support for offset parameter in dma_mmap() Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 26/86] iommu/vt-d: Fix ATSR handling for Root-Complex integrated endpoints Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 27/86] ext4: fix potential use after free in __ext4_journal_stop Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100
  [PATCH 3.13.y-ckt 30/86] vTPM: fix memory allocation flag for rtce buffer at kernel boot Kamal Mostafa <kamal@canonical.com> - 2015-12-03 00:30 +0100

csiph-web