Re: [PATCH] sunrpc: Don't use stack buffer with scatterlist

["J. Bruce Fields" <bfields@fieldses.org>]

On Fri, Aug 17, 2018 at 02:43:54PM -0700, Laura Abbott wrote:
> Fedora got a bug report from NFS:

Thanks, applying (unless Trond or Anna gets it).

--b.

> 
> kernel BUG at include/linux/scatterlist.h:143!
> ...
> RIP: 0010:sg_init_one+0x7d/0x90
> ..
>   make_checksum+0x4e7/0x760 [rpcsec_gss_krb5]
>   gss_get_mic_kerberos+0x26e/0x310 [rpcsec_gss_krb5]
>   gss_marshal+0x126/0x1a0 [auth_rpcgss]
>   ? __local_bh_enable_ip+0x80/0xe0
>   ? call_transmit_status+0x1d0/0x1d0 [sunrpc]
>   call_transmit+0x137/0x230 [sunrpc]
>   __rpc_execute+0x9b/0x490 [sunrpc]
>   rpc_run_task+0x119/0x150 [sunrpc]
>   nfs4_run_exchange_id+0x1bd/0x250 [nfsv4]
>   _nfs4_proc_exchange_id+0x2d/0x490 [nfsv4]
>   nfs41_discover_server_trunking+0x1c/0xa0 [nfsv4]
>   nfs4_discover_server_trunking+0x80/0x270 [nfsv4]
>   nfs4_init_client+0x16e/0x240 [nfsv4]
>   ? nfs_get_client+0x4c9/0x5d0 [nfs]
>   ? _raw_spin_unlock+0x24/0x30
>   ? nfs_get_client+0x4c9/0x5d0 [nfs]
>   nfs4_set_client+0xb2/0x100 [nfsv4]
>   nfs4_create_server+0xff/0x290 [nfsv4]
>   nfs4_remote_mount+0x28/0x50 [nfsv4]
>   mount_fs+0x3b/0x16a
>   vfs_kern_mount.part.35+0x54/0x160
>   nfs_do_root_mount+0x7f/0xc0 [nfsv4]
>   nfs4_try_mount+0x43/0x70 [nfsv4]
>   ? get_nfs_version+0x21/0x80 [nfs]
>   nfs_fs_mount+0x789/0xbf0 [nfs]
>   ? pcpu_alloc+0x6ca/0x7e0
>   ? nfs_clone_super+0x70/0x70 [nfs]
>   ? nfs_parse_mount_options+0xb40/0xb40 [nfs]
>   mount_fs+0x3b/0x16a
>   vfs_kern_mount.part.35+0x54/0x160
>   do_mount+0x1fd/0xd50
>   ksys_mount+0xba/0xd0
>   __x64_sys_mount+0x21/0x30
>   do_syscall_64+0x60/0x1f0
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> This is BUG_ON(!virt_addr_valid(buf)) triggered by using a stack
> allocated buffer with a scatterlist. Convert the buffer for
> rc4salt to be dynamically allocated instead.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1615258
> Signed-off-by: Laura Abbott <labbott@redhat.com>
> ---
> Compile tested only.
> ---
>  net/sunrpc/auth_gss/gss_krb5_crypto.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
> index 8654494b4d0a..834eb2b9e41b 100644
> --- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
> +++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
> @@ -169,7 +169,7 @@ make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
>  	struct scatterlist              sg[1];
>  	int err = -1;
>  	u8 *checksumdata;
> -	u8 rc4salt[4];
> +	u8 *rc4salt;
>  	struct crypto_ahash *md5;
>  	struct crypto_ahash *hmac_md5;
>  	struct ahash_request *req;
> @@ -183,14 +183,18 @@ make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
>  		return GSS_S_FAILURE;
>  	}
>  
> +	rc4salt = kmalloc_array(4, sizeof(*rc4salt), GFP_NOFS);
> +	if (!rc4salt)
> +		return GSS_S_FAILURE;
> +
>  	if (arcfour_hmac_md5_usage_to_salt(usage, rc4salt)) {
>  		dprintk("%s: invalid usage value %u\n", __func__, usage);
> -		return GSS_S_FAILURE;
> +		goto out_free_rc4salt;
>  	}
>  
>  	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
>  	if (!checksumdata)
> -		return GSS_S_FAILURE;
> +		goto out_free_rc4salt;
>  
>  	md5 = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC);
>  	if (IS_ERR(md5))
> @@ -258,6 +262,8 @@ make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
>  	crypto_free_ahash(md5);
>  out_free_cksum:
>  	kfree(checksumdata);
> +out_free_rc4salt:
> +	kfree(rc4salt);
>  	return err ? GSS_S_FAILURE : 0;
>  }
>  
> -- 
> 2.17.1