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    Subject[PATCH 5.4 173/215] fuse: ignore data argument of mount(..., MS_REMOUNT)
    Date
    From: Miklos Szeredi <mszeredi@redhat.com>

    commit e8b20a474cf2c42698d1942f939ff2128819f151 upstream.

    The command

    mount -o remount -o unknownoption /mnt/fuse

    succeeds on kernel versions prior to v5.4 and fails on kernel version at or
    after. This is because fuse_parse_param() rejects any unrecognised options
    in case of FS_CONTEXT_FOR_RECONFIGURE, just as for FS_CONTEXT_FOR_MOUNT.

    This causes a regression in case the fuse filesystem is in fstab, since
    remount sends all options found there to the kernel; even ones that are
    meant for the initial mount and are consumed by the userspace fuse server.

    Fix this by ignoring mount options, just as fuse_remount_fs() did prior to
    the conversion to the new API.

    Reported-by: Stefan Priebe <s.priebe@profihost.ag>
    Fixes: c30da2e981a7 ("fuse: convert to use the new mount API")
    Cc: <stable@vger.kernel.org> # v5.4
    Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/fuse/inode.c | 7 +++++++
    1 file changed, 7 insertions(+)

    --- a/fs/fuse/inode.c
    +++ b/fs/fuse/inode.c
    @@ -473,6 +473,13 @@ static int fuse_parse_param(struct fs_co
    struct fuse_fs_context *ctx = fc->fs_private;
    int opt;

    + /*
    + * Ignore options coming from mount(MS_REMOUNT) for backward
    + * compatibility.
    + */
    + if (fc->purpose == FS_CONTEXT_FOR_RECONFIGURE)
    + return 0;
    +
    opt = fs_parse(fc, &fuse_fs_parameters, param, &result);
    if (opt < 0)
    return opt;

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