[PATCH 3.16 234/366] cifs: Fix stack out-of-bounds in smb{2,3}_create_lease_buf()

Ben Hutchings
2018-11-11T20:12:49Z

From: Stefano Brivio <sbrivio@redhat.com>

commit 729c0c9dd55204f0c9a823ac8a7bfa83d36c7e78 upstream.

smb{2,3}_create_lease_buf() store a lease key in the lease
context for later usage on a lease break.

In most paths, the key is currently sourced from data that
happens to be on the stack near local variables for oplock in
SMB2_open() callers, e.g. from open_shroot(), whereas
smb2_open_file() properly allocates space on its stack for it.

The address of those local variables holding the oplock is then
passed to create_lease_buf handlers via SMB2_open(), and 16
bytes near oplock are used. This causes a stack out-of-bounds
access as reported by KASAN on SMB2.1 and SMB3 mounts (first
out-of-bounds access is shown here):

[ 111.528823] BUG: KASAN: stack-out-of-bounds in smb3_create_lease_buf+0x399/0x3b0 [cifs]
[ 111.530815] Read of size 8 at addr ffff88010829f249 by task mount.cifs/985
[ 111.532838] CPU: 3 PID: 985 Comm: mount.cifs Not tainted 4.18.0-rc3+ #91
[ 111.534656] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[ 111.536838] Call Trace:
[ 111.537528] dump_stack+0xc2/0x16b
[ 111.540890] print_address_description+0x6a/0x270
[ 111.542185] kasan_report+0x258/0x380
[ 111.544701] smb3_create_lease_buf+0x399/0x3b0 [cifs]
[ 111.546134] SMB2_open+0x1ef8/0x4b70 [cifs]
[ 111.575883] open_shroot+0x339/0x550 [cifs]
[ 111.591969] smb3_qfs_tcon+0x32c/0x1e60 [cifs]
[ 111.617405] cifs_mount+0x4f3/0x2fc0 [cifs]
[ 111.674332] cifs_smb3_do_mount+0x263/0xf10 [cifs]
[ 111.677915] mount_fs+0x55/0x2b0
[ 111.679504] vfs_kern_mount.part.22+0xaa/0x430
[ 111.684511] do_mount+0xc40/0x2660
[ 111.698301] ksys_mount+0x80/0xd0
[ 111.701541] do_syscall_64+0x14e/0x4b0
[ 111.711807] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 111.713665] RIP: 0033:0x7f372385b5fa
[ 111.715311] Code: 48 8b 0d 99 78 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 66 78 2c 00 f7 d8 64 89 01 48
[ 111.720330] RSP: 002b:00007ffff27049d8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[ 111.722601] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f372385b5fa
[ 111.724842] RDX: 000055c2ecdc73b2 RSI: 000055c2ecdc73f9 RDI: 00007ffff270580f
[ 111.727083] RBP: 00007ffff2705804 R08: 000055c2ee976060 R09: 0000000000001000
[ 111.729319] R10: 0000000000000000 R11: 0000000000000206 R12: 00007f3723f4d000
[ 111.731615] R13: 000055c2ee976060 R14: 00007f3723f4f90f R15: 0000000000000000

[ 111.735448] The buggy address belongs to the page:
[ 111.737420] page:ffffea000420a7c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
[ 111.739890] flags: 0x17ffffc0000000()
[ 111.741750] raw: 0017ffffc0000000 0000000000000000 dead000000000200 0000000000000000
[ 111.744216] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 111.746679] page dumped because: kasan: bad access detected

[ 111.750482] Memory state around the buggy address:
[ 111.752562] ffff88010829f100: 00 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00
[ 111.754991] ffff88010829f180: 00 00 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00
[ 111.757401] >ffff88010829f200: 00 00 00 00 00 f1 f1 f1 f1 01 f2 f2 f2 f2 f2 f2
[ 111.759801] ^
[ 111.762034] ffff88010829f280: f2 02 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00
[ 111.764486] ffff88010829f300: f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 111.766913] ==================================================================

Lease keys are however already generated and stored in fid data
on open and create paths: pass them down to the lease context
creation handlers and use them.

Suggested-by: Aurélien Aptel <aaptel@suse.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Fixes: b8c32dbb0deb ("CIFS: Request SMB2.1 leases")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/cifs/cifsglob.h | 2 +-
fs/cifs/smb2file.c | 11 ++++-------
fs/cifs/smb2ops.c | 9 +++------
fs/cifs/smb2pdu.c | 7 ++++---
fs/cifs/smb2pdu.h | 6 ++----
5 files changed, 14 insertions(+), 21 deletions(-)

--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -381,7 +381,7 @@ struct smb_version_operations {
void (*set_oplock_level)(struct cifsInodeInfo *, __u32, unsigned int,
bool *);
/* create lease context buffer for CREATE request */
- char * (*create_lease_buf)(u8 *, u8);
+ char * (*create_lease_buf)(u8 *lease_key, u8 oplock);
/* parse lease context buffer and return oplock/epoch info */
__u8 (*parse_lease_buf)(void *buf, unsigned int *epoch, char *lkey);
int (*clone_range)(const unsigned int, struct cifsFileInfo *src_file,
--- a/fs/cifs/smb2file.c
+++ b/fs/cifs/smb2file.c
@@ -41,7 +41,7 @@ smb2_open_file(const unsigned int xid, s
int rc;
__le16 *smb2_path;
struct smb2_file_all_info *smb2_data = NULL;
- __u8 smb2_oplock[17];
+ __u8 smb2_oplock;
struct cifs_fid *fid = oparms->fid;

smb2_path = cifs_convert_path_to_utf16(oparms->path, oparms->cifs_sb);
@@ -58,12 +58,9 @@ smb2_open_file(const unsigned int xid, s
}

oparms->desired_access |= FILE_READ_ATTRIBUTES;
- *smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;
+ smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;

- if (oparms->tcon->ses->server->capabilities & SMB2_GLOBAL_CAP_LEASING)
- memcpy(smb2_oplock + 1, fid->lease_key, SMB2_LEASE_KEY_SIZE);
-
- rc = SMB2_open(xid, oparms, smb2_path, smb2_oplock, smb2_data, NULL);
+ rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL);
if (rc)
goto out;

@@ -80,7 +77,7 @@ smb2_open_file(const unsigned int xid, s
move_smb2_info_to_cifs(buf, smb2_data);
}

- *oplock = *smb2_oplock;
+ *oplock = smb2_oplock;
out:
kfree(smb2_data);
kfree(smb2_path);
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1072,8 +1072,7 @@ smb2_create_lease_buf(u8 *lease_key, u8
if (!buf)
return NULL;

- buf->lcontext.LeaseKeyLow = cpu_to_le64(*((u64 *)lease_key));
- buf->lcontext.LeaseKeyHigh = cpu_to_le64(*((u64 *)(lease_key + 8)));
+ memcpy(&buf->lcontext.LeaseKey, lease_key, SMB2_LEASE_KEY_SIZE);
buf->lcontext.LeaseState = map_oplock_to_lease(oplock);

buf->ccontext.DataOffset = cpu_to_le16(offsetof
@@ -1099,8 +1098,7 @@ smb3_create_lease_buf(u8 *lease_key, u8
if (!buf)
return NULL;

- buf->lcontext.LeaseKeyLow = cpu_to_le64(*((u64 *)lease_key));
- buf->lcontext.LeaseKeyHigh = cpu_to_le64(*((u64 *)(lease_key + 8)));
+ memcpy(&buf->lcontext.LeaseKey, lease_key, SMB2_LEASE_KEY_SIZE);
buf->lcontext.LeaseState = map_oplock_to_lease(oplock);

buf->ccontext.DataOffset = cpu_to_le16(offsetof
@@ -1137,8 +1135,7 @@ smb3_parse_lease_buf(void *buf, unsigned
if (lc->lcontext.LeaseFlags & SMB2_LEASE_FLAG_BREAK_IN_PROGRESS)
return SMB2_OPLOCK_LEVEL_NOCHANGE;
if (lease_key)
- memcpy(lease_key, &lc->lcontext.LeaseKeyLow,
- SMB2_LEASE_KEY_SIZE);
+ memcpy(lease_key, &lc->lcontext.LeaseKey, SMB2_LEASE_KEY_SIZE);
return le32_to_cpu(lc->lcontext.LeaseState);
}

--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -1084,12 +1084,12 @@ parse_lease_state(struct TCP_Server_Info

static int
add_lease_context(struct TCP_Server_Info *server, struct kvec *iov,
- unsigned int *num_iovec, __u8 *oplock)
+ unsigned int *num_iovec, u8 *lease_key, __u8 *oplock)
{
struct smb2_create_req *req = iov[0].iov_base;
unsigned int num = *num_iovec;

- iov[num].iov_base = server->ops->create_lease_buf(oplock+1, *oplock);
+ iov[num].iov_base = server->ops->create_lease_buf(lease_key, *oplock);
if (iov[num].iov_base == NULL)
return -ENOMEM;
iov[num].iov_len = server->vals->create_lease_size;
@@ -1212,7 +1212,8 @@ SMB2_open(const unsigned int xid, struct
*oplock == SMB2_OPLOCK_LEVEL_NONE)
req->RequestedOplockLevel = *oplock;
else {
- rc = add_lease_context(server, iov, &num_iovecs, oplock);
+ rc = add_lease_context(server, iov, &num_iovecs,
+ oparms->fid->lease_key, oplock);
if (rc) {
cifs_small_buf_release(req);
kfree(copy_path);
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -510,16 +510,14 @@ struct create_context {
#define SMB2_LEASE_KEY_SIZE 16

struct lease_context {
- __le64 LeaseKeyLow;
- __le64 LeaseKeyHigh;
+ u8 LeaseKey[SMB2_LEASE_KEY_SIZE];
__le32 LeaseState;
__le32 LeaseFlags;
__le64 LeaseDuration;
} __packed;

struct lease_context_v2 {
- __le64 LeaseKeyLow;
- __le64 LeaseKeyHigh;
+ u8 LeaseKey[SMB2_LEASE_KEY_SIZE];
__le32 LeaseState;
__le32 LeaseFlags;
__le64 LeaseDuration;