Commit 98283bb4 authored by OGAWA Hirofumi's avatar OGAWA Hirofumi Committed by Linus Torvalds
Browse files

fat: Fix the race of read/write the FAT12 entry 



FAT12 entry is 12bits, so it needs 2 phase to update the value.  And
writer and reader access it without any lock, so reader can get the
half updated value.

This fixes the long standing race condition by adding a global
spinlock to only FAT12 for avoiding any impact against FAT16/32.

Signed-off-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 347e03df

fs/fat/fatent.c

+7 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ struct fatent_operations { 
	int (*ent_next)(struct fat_entry *);

};



static DEFINE_SPINLOCK(fat12_entry_lock);



static void fat12_ent_blocknr(struct super_block *sb, int entry,

			      int *offset, sector_t *blocknr)

{
@@ -116,10 +118,13 @@ static int fat12_ent_get(struct fat_entry *fatent) 
	u8 **ent12_p = fatent->u.ent12_p;

	int next;



	spin_lock(&fat12_entry_lock);

	if (fatent->entry & 1)

		next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);

	else

		next = (*ent12_p[1] << 8) | *ent12_p[0];

	spin_unlock(&fat12_entry_lock);



	next &= 0x0fff;

	if (next >= BAD_FAT12)

		next = FAT_ENT_EOF;
@@ -151,6 +156,7 @@ static void fat12_ent_put(struct fat_entry *fatent, int new) 
	if (new == FAT_ENT_EOF)

		new = EOF_FAT12;



	spin_lock(&fat12_entry_lock);

	if (fatent->entry & 1) {

		*ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);

		*ent12_p[1] = new >> 4;
@@ -158,6 +164,7 @@ static void fat12_ent_put(struct fat_entry *fatent, int new) 
		*ent12_p[0] = new & 0xff;

		*ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);

	}

	spin_unlock(&fat12_entry_lock);



	mark_buffer_dirty(fatent->bhs[0]);

	if (fatent->nr_bhs == 2)

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