Commit message: rds: Fix NULL pointer dereference in __rds_rdma_map

This is a fix for syzkaller719569, where memory registration was
attempted without any underlying transport being loaded.

Analysis of the case reveals that it is the setsockopt() RDS_GET_MR
(2) and RDS_GET_MR_FOR_DEST (7) that are vulnerable.

Here is an example stack trace when the bug is hit:

BUG: unable to handle kernel NULL pointer dereference at 00000000000000c0
IP: __rds_rdma_map+0x36/0x440 [rds]
PGD 2f93d03067 P4D 2f93d03067 PUD 2f93d02067 PMD 0
Oops: 0000 [#1] SMP
Modules linked in: bridge stp llc tun rpcsec_gss_krb5 nfsv4
dns_resolver nfs fscache rds binfmt_misc sb_edac intel_powerclamp
coretemp kvm_intel kvm irqbypass crct10dif_pclmul c rc32_pclmul
ghash_clmulni_intel pcbc aesni_intel crypto_simd glue_helper cryptd
iTCO_wdt mei_me sg iTCO_vendor_support ipmi_si mei ipmi_devintf nfsd
shpchp pcspkr i2c_i801 ioatd ma ipmi_msghandler wmi lpc_ich mfd_core
auth_rpcgss nfs_acl lockd grace sunrpc ip_tables ext4 mbcache jbd2
mgag200 i2c_algo_bit drm_kms_helper ixgbe syscopyarea ahci sysfillrect
sysimgblt libahci mdio fb_sys_fops ttm ptp libata sd_mod mlx4_core drm
crc32c_intel pps_core megaraid_sas i2c_core dca dm_mirror
dm_region_hash dm_log dm_mod
CPU: 48 PID: 45787 Comm: repro_set2 Not tainted 4.14.2-3.el7uek.x86_64 #2
Hardware name: Oracle Corporation ORACLE SERVER X5-2L/ASM,MOBO TRAY,2U, BIOS 31110000 03/03/2017
task: ffff882f9190db00 task.stack: ffffc9002b994000
RIP: 0010:__rds_rdma_map+0x36/0x440 [rds]
RSP: 0018:ffffc9002b997df0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff882fa2182580 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffc9002b997e40 RDI: ffff882fa2182580
RBP: ffffc9002b997e30 R08: 0000000000000000 R09: 0000000000000002
R10: ffff885fb29e3838 R11: 0000000000000000 R12: ffff882fa2182580
R13: ffff882fa2182580 R14: 0000000000000002 R15: 0000000020000ffc
FS:  00007fbffa20b700(0000) GS:ffff882fbfb80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000000c0 CR3: 0000002f98a66006 CR4: 00000000001606e0
Call Trace:
 rds_get_mr+0x56/0x80 [rds]
 rds_setsockopt+0x172/0x340 [rds]
 ? __fget_light+0x25/0x60
 ? __fdget+0x13/0x20
 SyS_setsockopt+0x80/0xe0
 do_syscall_64+0x67/0x1b0
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7fbff9b117f9
RSP: 002b:00007fbffa20aed8 EFLAGS: 00000293 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00000000000c84a4 RCX: 00007fbff9b117f9
RDX: 0000000000000002 RSI: 0000400000000114 RDI: 000000000000109b
RBP: 00007fbffa20af10 R08: 0000000000000020 R09: 00007fbff9dd7860
R10: 0000000020000ffc R11: 0000000000000293 R12: 0000000000000000
R13: 00007fbffa20b9c0 R14: 00007fbffa20b700 R15: 0000000000000021

Code: 41 56 41 55 49 89 fd 41 54 53 48 83 ec 18 8b 87 f0 02 00 00 48
89 55 d0 48 89 4d c8 85 c0 0f 84 2d 03 00 00 48 8b 87 00 03 00 00 <48>
83 b8 c0 00 00 00 00 0f 84 25 03 00 0 0 48 8b 06 48 8b 56 08

The fix is to check the existence of an underlying transport in
__rds_rdma_map().

Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2018-7492
CWE: CWE-476
Vulnerability description: A NULL pointer dereference was found in the net/rds/rdma.c __rds_rdma_map() function in the Linux kernel before 4.14.7 allowing local attackers to cause a system panic and a denial-of-service, related to RDS_GET_MR and RDS_GET_MR_FOR_DEST.

Project: linux
File: rdma.c

int rds_free_mr(struct rds_sock *rs, char __user *optval, int optlen)
{
	struct rds_free_mr_args args;
	struct rds_mr *mr;
	unsigned long flags;

	if (optlen != sizeof(struct rds_free_mr_args))
		return -EINVAL;

	if (copy_from_user(&args, (struct rds_free_mr_args __user *)optval,
			   sizeof(struct rds_free_mr_args)))
		return -EFAULT;

	/* Special case - a null cookie means flush all unused MRs */
	if (args.cookie == 0) {
		if (!rs->rs_transport || !rs->rs_transport->flush_mrs)
			return -EINVAL;
		rs->rs_transport->flush_mrs();
		return 0;
	}

	/* Look up the MR given its R_key and remove it from the rbtree
	 * so nobody else finds it.
	 * This should also prevent races with rds_rdma_unuse.
	 */
	spin_lock_irqsave(&rs->rs_rdma_lock, flags);
	mr = rds_mr_tree_walk(&rs->rs_rdma_keys, rds_rdma_cookie_key(args.cookie), NULL);
	if (mr) {
		rb_erase(&mr->r_rb_node, &rs->rs_rdma_keys);
		RB_CLEAR_NODE(&mr->r_rb_node);
		if (args.flags & RDS_RDMA_INVALIDATE)
			mr->r_invalidate = 1;
	}
	spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);

	if (!mr)
		return -EINVAL;

	/*
	 * call rds_destroy_mr() ourselves so that we're sure it's done by the time
	 * we return.  If we let rds_mr_put() do it it might not happen until
	 * someone else drops their ref.
	 */
	rds_destroy_mr(mr);
	rds_mr_put(mr);
	return 0;
}

Project: linux
File: rdma.c

int rds_get_mr(struct rds_sock *rs, char __user *optval, int optlen)
{
	struct rds_get_mr_args args;

	if (optlen != sizeof(struct rds_get_mr_args))
		return -EINVAL;

	if (copy_from_user(&args, (struct rds_get_mr_args __user *)optval,
			   sizeof(struct rds_get_mr_args)))
		return -EFAULT;

	return __rds_rdma_map(rs, &args, NULL, NULL);
}

Project: linux
File: rdma.c

static struct rds_mr *rds_mr_tree_walk(struct rb_root *root, u64 key,
				       struct rds_mr *insert)
{
	struct rb_node **p = &root->rb_node;
	struct rb_node *parent = NULL;
	struct rds_mr *mr;

	while (*p) {
		parent = *p;
		mr = rb_entry(parent, struct rds_mr, r_rb_node);

		if (key < mr->r_key)
			p = &(*p)->rb_left;
		else if (key > mr->r_key)
			p = &(*p)->rb_right;
		else
			return mr;
	}

	if (insert) {
		rb_link_node(&insert->r_rb_node, parent, p);
		rb_insert_color(&insert->r_rb_node, root);
		refcount_inc(&insert->r_refcount);
	}
	return NULL;
}