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

[Ziran Zhang <zhangcoder@yeah.net>]

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>
---

> 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);
-- 
2.43.0