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List:       busybox
Subject:    Re: [PATCH] mkfs.vfat: fix volume label to be padded with space
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2022-01-23 22:06:50
Message-ID: CAK1hOcPdwKNJcV4dchg=GyixW0u10EJpM4m264uikrrDuBp7kw () mail ! gmail ! com
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Applied, thank you

On Fri, Jan 21, 2022 at 12:17 PM Timo Teräs <timo.teras@iki.fi> wrote:
>
> The specification requires volume label to be zero padded.
>
> Latest fsck.vfat will remove the zero padded volume label
> as invalid. See also:
> https://github.com/dosfstools/dosfstools/issues/172
>
> Make the default label also "NO NAME" which has the special meaning
> that label is not set.
>
> function                                             old     new   delta
> mkfs_vfat_main                                      1546    1665    +119
> .rodata                                            79474   79480      +6
> ------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 2/0 up/down: 125/0)             Total: 125 bytes
> ---
> Also the volume label should not contain certain special character, or
> low case alphabet. However, seems lower case is allowed still by default
> in fsck.vfat, and the special characters are a bit of corner case. So I
> decided to not add checking for these.
>
>  util-linux/mkfs_vfat.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/util-linux/mkfs_vfat.c b/util-linux/mkfs_vfat.c
> index 844d965f8..fc256b903 100644
> --- a/util-linux/mkfs_vfat.c
> +++ b/util-linux/mkfs_vfat.c
> @@ -219,7 +219,8 @@ int mkfs_vfat_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
>  int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
>  {
>         struct stat st;
> -       const char *volume_label = "";
> +       const char *arg_volume_label = "NO NAME    ";
> +       char volume_label[12];
>         char *buf;
>         char *device_name;
>         uoff_t volume_size_bytes;
> @@ -258,13 +259,14 @@ int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
>                 "Ab:cCf:F:h:Ii:l:m:n:r:R:s:S:v"
>                 "\0" "-1", //:b+:f+:F+:h+:r+:R+:s+:S+:vv:c--l:l--c
>                 NULL, NULL, NULL, NULL, NULL,
> -               NULL, NULL, &volume_label, NULL, NULL, NULL, NULL);
> +               NULL, NULL, &arg_volume_label, NULL, NULL, NULL, NULL);
>         argv += optind;
>
>         // cache device name
>         device_name = argv[0];
>         // default volume ID = creation time
>         volume_id = time(NULL);
> +       snprintf(volume_label, sizeof(volume_label), "%-11s", arg_volume_label);
>
>         dev = xopen(device_name, O_RDWR);
>         xfstat(dev, &st, device_name);
> @@ -508,7 +510,7 @@ int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
>                 STORE_LE(boot_blk->vi.ext_boot_sign, 0x29);
>                 STORE_LE(boot_blk->vi.volume_id32, volume_id);
>                 memcpy(boot_blk->vi.fs_type, "FAT32   ", sizeof(boot_blk->vi.fs_type));
> -               strncpy(boot_blk->vi.volume_label, volume_label, sizeof(boot_blk->vi.volume_label));
> +               memcpy(boot_blk->vi.volume_label, volume_label, sizeof(boot_blk->vi.volume_label));
>                 memcpy(boot_blk->boot_code, boot_code, sizeof(boot_code));
>                 STORE_LE(boot_blk->boot_sign, BOOT_SIGN);
>
> @@ -553,7 +555,7 @@ int mkfs_vfat_main(int argc UNUSED_PARAM, char **argv)
>                 uint16_t t, d;
>  #endif
>                 de = (void*)buf;
> -               strncpy(de->name, volume_label, sizeof(de->name));
> +               memcpy(de->name, volume_label, sizeof(de->name));
>                 STORE_LE(de->attr, ATTR_VOLUME);
>  #if 0
>                 localtime_r(&create_time, &tm_time);
> --
> 2.34.1
>
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