[PATCH stable] cifs: empty TargetInfo leads to crash on recovery

From: Dan Aloni
Date: Sat Jan 27 2018 - 15:09:32 EST

commit cabfb3680f78 upstream.

[ resend from Oct 20, 2014, see [1] ]

A trivially patched Samba server (see [2] [3]) can cause a remote kernel
crash (see [4]) in a client's CIFS kernel module upon session recovery,
under kernels prior to v4.11. The server patch can made by a single
source line modification - returning an empty TargetInfo in an NTLMSSP
setup negotiation response.

To reproduce at the client side, the CIFS client can be instructed to
mount with SMB 2.0, on a share without user/password credentials, e.g:

mount -t cifs //[host]/[share] -o vers=2.0,guest [mountpoint]

(It may also reproduce with credentials, but I used a simpler
configuration for the reproduction)

An demo patch to Samba 4.7.4 is provided in the links provided.

As for the client crash itself:

When the session is recovered (after a server start/stop, for example),
the following condition turns out to be true:

ses->auth_key.len != 0 && ses->auth_key.response == NULL

This will cause the following memcpy() in setup_ntlmv2_rsp() to GPF,
because tiblob == NULL and tilen != 0 (these are the old auth_key values):

memcpy(ses->auth_key.response + baselen, tiblob, tilen);

By bisecting, upstream commit cabfb3680f78 ("CIFS: Enable encryption
during session setup phase") from v4.11 have fixed this issue.

According to my tests, LTS kernels versions 4.4.x and 4.9.x are affected.
The patch below applies for 4.4.x however a similar patch can be applied
to 4.9.x and older kernels.

Signed-off-by: Dan Aloni <dan@xxxxxxxxxxxx>
CC: Steve French <sfrench@xxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx # 4.4.x
CC: linux-cifs@xxxxxxxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx

[1]
https://patchwork.kernel.org/patch/5106391/

[2] (temporary url)
http://copr-dist-git.fedorainfracloud.org/cgit/alonid/samba-for-client-crash-repro/samba.git/tree/0001-Patch.patch?id=43229c84abe008bfc11aa86f5bacb03a1e54f88c

[3] (temporary url)
https://copr.fedorainfracloud.org/coprs/alonid/samba-for-client-crash-repro/

[4]
[ 3414.518134] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 3414.518200] IP: memcpy_erms+0x6/0x10
[ 3414.518227] PGD 0

[ 3414.518252] Oops: 0000 [#1] SMP
[ 3414.518272] Modules linked in: arc4 md4 cifs rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw ebtable_filter ebtables ip6table_filter ip6_tables snd_hda_codec_generic ppdev snd_hda_intel snd_hda_codec crct10dif_pclmul crc32_pclmul snd_hwdep snd_hda_core ghash_clmulni_intel snd_seq snd_seq_device snd_pcm joydev parport_pc tpm_tis parport tpm_tis_core tpm snd_timer snd soundcore qemu_fw_cfg virtio_balloon i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c
[ 3414.518708] virtio_blk virtio_console virtio_net qxl drm_kms_helper ttm crc32c_intel drm ata_generic nvme serio_raw nvme_core virtio_pci virtio_ring virtio pata_acpi
[ 3414.518803] CPU: 3 PID: 1697 Comm: kworker/3:1 Not tainted 4.10.0-rc6-dan-00097-ge765a3d89ede #20
[ 3414.518852] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-2.fc27 04/01/2014
[ 3414.518927] Workqueue: cifsiod smb2_reconnect_server [cifs]
[ 3414.518960] task: ffff8cc6764a4000 task.stack: ffff9bc548808000
[ 3414.518997] RIP: 0010:memcpy_erms+0x6/0x10
[ 3414.519021] RSP: 0018:ffff9bc54880bbc8 EFLAGS: 00010296
[ 3414.519051] RAX: ffff8cc6ba00d8dc RBX: ffff8cc676190400 RCX: 0000000000000010
[ 3414.519091] RDX: 0000000000000010 RSI: 0000000000000000 RDI: ffff8cc6ba00d8dc
[ 3414.519130] RBP: ffff9bc54880bc30 R08: ffff9bc54880bb58 R09: ffff9bc54880bb58
[ 3414.519170] R10: 000000004619520e R11: 00000000f46cd8cf R12: 0000000000000000
[ 3414.519209] R13: 0000000000000000 R14: ffff8cc6ba00d8a0 R15: 0000000000000010
[ 3414.519250] FS: 0000000000000000(0000) GS:ffff8cc6bfd80000(0000) knlGS:0000000000000000
[ 3414.519314] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3414.519347] CR2: 0000000000000000 CR3: 000000007992a000 CR4: 00000000003406e0
[ 3414.519392] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 3414.519431] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 3414.519470] Call Trace:
[ 3414.519510] ? setup_ntlmv2_rsp+0x124/0xa10 [cifs]
[ 3414.519553] build_ntlmssp_auth_blob+0x36/0x310 [cifs]
[ 3414.519597] SMB2_sess_auth_rawntlmssp_authenticate+0xc7/0x300 [cifs]
[ 3414.519646] SMB2_sess_setup+0x9a/0x140 [cifs]
[ 3414.519685] cifs_setup_session+0x78/0x100 [cifs]
[ 3414.519722] ? cifs_negotiate_protocol+0x84/0xd0 [cifs]
[ 3414.519763] smb2_reconnect+0x308/0x3e0 [cifs]
[ 3414.519793] ? __internal_add_timer+0x1f/0x60
[ 3414.519831] smb2_reconnect_server+0x187/0x260 [cifs]
[ 3414.519863] process_one_work+0x19e/0x440
[ 3414.519887] worker_thread+0x4e/0x4a0
[ 3414.519910] ? process_one_work+0x440/0x440
[ 3414.519936] kthread+0x11e/0x140
[ 3414.520493] ? kthread_park+0x90/0x90
[ 3414.520989] ret_from_fork+0x2c/0x40
[ 3414.521450] Code: 78 ff ff ff 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 <f3> a4 c3 0f 1f 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38
[ 3414.522488] RIP: memcpy_erms+0x6/0x10 RSP: ffff9bc54880bbc8
[ 3414.522964] CR2: 0000000000000000
[ 3414.526127] ---[ end trace bbe4aa1e45cc6c17 ]---
---
fs/cifs/smb2pdu.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index f2ff60e58ec8..91c9e83df457 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -633,6 +633,7 @@ SMB2_sess_setup(const unsigned int xid, struct cifs_ses *ses,
*/
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;

/*
* If memory allocation is successful, caller of this function
@@ -837,6 +838,7 @@ ssetup_exit:
rc = server->ops->generate_signingkey(ses);
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;
if (rc) {
cifs_dbg(FYI,
"SMB3 session key generation failed\n");
@@ -861,6 +863,7 @@ keygen_exit:
if (!server->sign) {
kfree(ses->auth_key.response);
ses->auth_key.response = NULL;
+ ses->auth_key.len = 0;
}
if (spnego_key) {
key_invalidate(spnego_key);
--
2.14.3