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>

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

[OGAWA Hirofumi]

OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:

Please apply this too.

Thanks.

> 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>