Re: [PATCH v4] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

Re: [PATCH v4] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[OGAWA Hirofumi]

Ziran Zhang <zhangcoder@yeah.net> writes:

> The fat_read_static_bpb() only accepts a short jump as a valid
> bootstrap code signature for DOS 1.x volumes when the dos1xfloppy
> mount option is used.
>
> However, according to the Microsoft fatgen103.doc, the BS_jmpBoot
> field has two allowed forms: 0xEB 0x?? 0x90 (short jump + NOP)
> and 0xE9 0x?? 0x?? (near jump). The specification explicitly states
> that either form is acceptable.
>
> This patch relaxes the check to also accept 0xE9 as the first byte of
> the jump instruction.
>
> Changes in v4:
> - Add original commit log
>
> Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>

Thanks.

Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

> ---
>
>> Could you add original commit log, instead of changelog?
>> 
>> Thanks.
>
> Done! Please ignore the earlier erroneous v2 v2 and v3.
>
>  fs/fat/inode.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 28f78df08..0e7d106ea 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
>  	int error = -EINVAL;
>  	unsigned i;
>  
> -	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
> -	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
> +	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
> +	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
> +	    (b->ignored[0] != 0xe9)) {
>  		if (!silent)
>  			fat_msg(sb, KERN_ERR,
>  				"%s; no bootstrapping code", notdos1x);

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>