Re: [PATCH v3] nfs: keep server info for remounts

[Jeff Layton]

On Sun, 2024-04-14 at 19:01 +0200, Martin Kaiser wrote:
> With newer kernels that use fs_context for nfs mounts, remounts fail with
> -EINVAL.
> 
> $ mount -t nfs -o nolock 10.0.0.1:/tmp/test /mnt/test/
> $ mount -t nfs -o remount /mnt/test/
> mount: mounting 10.0.0.1:/tmp/test on /mnt/test failed: Invalid argument
> 
> For remounts, the nfs server address and port are populated by
> nfs_init_fs_context and later overwritten with 0x00 bytes by
> nfs23_parse_monolithic. The remount then fails as the server address is
> invalid.
> 
> Fix this by not overwriting nfs server info in nfs23_parse_monolithic if
> we're doing a remount.
> 
> Fixes: f2aedb713c28 ("NFS: Add fs_context support.")
> Signed-off-by: Martin Kaiser <martin@xxxxxxxxx>
> ---
>  v3:
>  - rebased against linux-next from 12th April 2024
> 
>  v2:
>  - rebased against linux-next from 26th February 2024
> 
> Dear all,
> I'm resending this patch again. The problem that I'm trying to fix is still
> present in linux-next. Thanks in advance for any reviews and comments.
> 
> I guess that we're taking this path for remounts
> 
> do_remount
>     fs_context_for_reconfigure
>         alloc_fs_context
>             init_fs_context == nfs_init_fs_context
>                fc->root is set for remounts
>                ctx->nfs_server is populated
>     parse_monolithic_mount_data
>         nfs_fs_context_parse_monolithic
>             nfs23_parse_monolithic
>                ctx->nfs_server is overwritten with data from mount request
> 
> An alternative to checking for !is_remount_fc(fc) would be to check
> if (ctx->nfs_server.addrlen == 0)
> 
> fs/nfs/fs_context.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
> index d0a0956f8a13..cac1157be2c2 100644
> --- a/fs/nfs/fs_context.c
> +++ b/fs/nfs/fs_context.c
> @@ -1112,9 +1112,12 @@ static int nfs23_parse_monolithic(struct fs_context *fc,
>  		ctx->acdirmax	= data->acdirmax;
>  		ctx->need_mount	= false;
>  
> -		memcpy(sap, &data->addr, sizeof(data->addr));
> -		ctx->nfs_server.addrlen = sizeof(data->addr);
> -		ctx->nfs_server.port = ntohs(data->addr.sin_port);
> +		if (!is_remount_fc(fc)) {
> +			memcpy(sap, &data->addr, sizeof(data->addr));
> +			ctx->nfs_server.addrlen = sizeof(data->addr);
> +			ctx->nfs_server.port = ntohs(data->addr.sin_port);
> +		}
> +
>  		if (sap->ss_family != AF_INET ||
>  		    !nfs_verify_server_address(sap))
>  			goto out_no_address;

Doesn't nfs4_parse_monolithic need the same fix? 
-- 
Jeff Layton <jlayton@xxxxxxxxxx>