[PATCH] cifs: don't call cifs_lookup from atomic open with a hashed negative dentry

[Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

The following oops was reported by Vit Zahradka. The BUG is this in
__d_rehash():

    BUG_ON(!d_unhashed(entry));

:kernel BUG at fs/dcache.c:2138!
:invalid opcode: 0000 [#1] SMP
:Modules linked in: fuse ebtable_nat ebtables ipt_MASQUERADE iptable_nat
nf_nat des_generic xt_CHECKSUM iptable_mangle md4 bridge stp llc nls_utf8
cifs dns_resolver fscache lockd sunrpc rfcomm bnep be2iscsi
iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi
ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_mad ib_core iscsi_tcp
libiscsi_tcp libiscsi scsi_transport_iscsi ip6t_REJECT nf_conntrack_ipv6
nf_defrag_ipv6 ip6table_filter ip6_tables nf_conntrack_ipv4 nf_defrag_ipv4
xt_state nf_conntrack snd_hda_codec_conexant btusb bluetooth snd_hda_intel
snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm thinkpad_acpi
snd_page_alloc arc4 snd_timer iwldvm mac80211 iwlwifi cfg80211 uvcvideo
videobuf2_vmalloc videobuf2_memops videobuf2_core videodev snd media rfkill
soundcore i2c_i801 mei r592 memstick iTCO_wdt iTCO_vendor_support lpc_ich
tg3 coretemp microcode ppdev parport_pc parport vhost_net tun macvtap
macvlan kvm_intel kvm uinput binfmt_misc firewire_oh
:ci firewire_core crc_itu_t sdhci_pci sdhci mmc_core yenta_socket wmi video
radeon i2c_algo_bit drm_kms_helper ttm drm i2c_core
:Pid: 2219, comm: eclipse Not tainted 3.6.1-1.fc17.i686 #1 LENOVO
27326FG/27326FG
:EIP: 0060:[<c0557577>] EFLAGS: 00010282 CPU: 1
:EIP is at __d_rehash+0x57/0x60
:EAX: ee641c80 EBX: 0000096a ECX: f7338208 EDX: f7338208
:ESI: fffffffe EDI: f6339f60 EBP: f0481d84 ESP: f0481d80
: DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
:CR0: 8005003b CR2: 06567f84 CR3: 30710000 CR4: 000027d0
:DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
:DR6: ffff0ff0 DR7: 00000400
:Process eclipse (pid: 2219, ti=f0480000 task=f0490c90 task.ti=f0480000)
:Stack:
: 0000096a f0481d90 c05575b2 ee641c80 f0481d9c c05575da 00000000 f0481dd8
: f9c01e32 f0734000 00004213 00000000 f0734000 f0481df4 f11ce600 00004213
: f6b07c60 00000000 00000000 f0481ef8 ee641c80 ef1781e0 f0481e20 f9c01f52
:Call Trace:
: [<c05575b2>] _d_rehash+0x32/0x40
: [<c05575da>] d_rehash+0x1a/0x30
: [<f9c01e32>] cifs_lookup+0x212/0x300 [cifs]
: [<f9c01f52>] cifs_atomic_open+0x32/0x200 [cifs]
: [<c05584bf>] ? d_lookup+0x2f/0x50
: [<c055074c>] do_last+0x42c/0xbd0
: [<c054dd8c>] ? link_path_walk+0x1dc/0x750
: [<c0550f8d>] path_openat+0x9d/0x3b0
: [<c046d47f>] ? wake_up_state+0xf/0x20
: [<c0490ed2>] ? wake_futex+0x32/0x50
: [<c046fcb5>] ? __dequeue_entity+0x25/0x40
: [<c0551481>] do_filp_open+0x31/0x80
: [<c055bdfc>] ? alloc_fd+0x3c/0xe0
: [<c054c970>] ? getname_flags+0x40/0xd0
: [<c0542885>] do_sys_open+0xe5/0x1c0
: [<c05429d0>] sys_openat+0x30/0x40
: [<c095addf>] sysenter_do_call+0x12/0x28
:Code: 48 08 74 03 89 59 04 f6 c3 01 89 50 0c 75 20 f6 02 01 74 19 83 cb 01
89 1a 0f ba 32 00 5b 5d c3 f3 90 8b 0a 80 e1 01 75 f7 eb b9 <0f> 0b 0f 0b
0f 0b 8d 76 00 55 89 e5 53 66 66 66 66 90 8b 0d fc
:EIP: [<c0557577>] __d_rehash+0x57/0x60 SS:ESP 0068:f0481d80

I think what happened is something like the following:

openat() was called on the file without O_CREAT. A negative dentry was
already in the cache, and was successfully revalidated. At that point a
hashed, negative dentry was passed to cifs_atomic_open. Since O_CREAT
wasn't set, it punted it over to cifs_lookup which did a lookup and then
tried to rehash the result and tripped over the bug.

Fix this by simply returning -ENOENT in this case instead of calling
cifs_lookup. For the longer term, I think cifs_atomic_open could use
some cleanup. There is probably no reason to limit atomic opens to the
O_CREAT case.

Cc: <stable-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> # 3.6.x
Reported-and-Tested-by: Vit Zahradka <vit.zahradka-IWqWACnzNjzrBKCeMvbIDA@public.gmane.org>
Signed-off-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 fs/cifs/dir.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index 7c0a812..5da95d3 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -398,7 +398,12 @@ cifs_atomic_open(struct inode *inode, struct dentry *direntry,
 	 * in network traffic in the other paths.
 	 */
 	if (!(oflags & O_CREAT)) {
-		struct dentry *res = cifs_lookup(inode, direntry, 0);
+		struct dentry *res;
+
+		if (!direntry->d_inode)
+			return -ENOENT;
+
+		res = cifs_lookup(inode, direntry, 0);
 		if (IS_ERR(res))
 			return PTR_ERR(res);
 
-- 
1.7.11.7