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Subject[PATCH 19/21] fat: mmu_private race fix
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mmu_private is 64bits value, hence it's not atomic to update.

So, the access rule for mmu_private is we must hold ->i_mutex. But,
fat_get_block() path doesn't follow the rule on non-allocation path.

This fixes by using i_size instead if non-allocation path.

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

fs/fat/cache.c | 23 ++++++++++++++++++-----
fs/fat/dir.c | 2 +-
fs/fat/fat.h | 6 ++++--
fs/fat/inode.c | 4 ++--
4 files changed, 25 insertions(+), 10 deletions(-)

diff -puN fs/fat/cache.c~fat-mmu_private-race-fix fs/fat/cache.c
--- linux-2.6/fs/fat/cache.c~fat-mmu_private-race-fix 2008-09-29 13:58:53.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/cache.c 2008-09-29 19:08:39.000000000 +0900
@@ -293,10 +293,12 @@ static int fat_bmap_cluster(struct inode
}

int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
- unsigned long *mapped_blocks)
+ unsigned long *mapped_blocks, int create)
{
struct super_block *sb = inode->i_sb;
struct msdos_sb_info *sbi = MSDOS_SB(sb);
+ const unsigned long blocksize = sb->s_blocksize;
+ const unsigned char blocksize_bits = sb->s_blocksize_bits;
sector_t last_block;
int cluster, offset;

@@ -309,10 +311,21 @@ int fat_bmap(struct inode *inode, sector
}
return 0;
}
- last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
- >> sb->s_blocksize_bits;
- if (sector >= last_block)
- return 0;
+
+ last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
+ if (sector >= last_block) {
+ if (!create)
+ return 0;
+
+ /*
+ * ->mmu_private can access on only allocation path.
+ * (caller must hold ->i_mutex)
+ */
+ last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
+ >> blocksize_bits;
+ if (sector >= last_block)
+ return 0;
+ }

cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
offset = sector & (sbi->sec_per_clus - 1);
diff -puN fs/fat/dir.c~fat-mmu_private-race-fix fs/fat/dir.c
--- linux-2.6/fs/fat/dir.c~fat-mmu_private-race-fix 2008-09-29 13:58:53.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/dir.c 2008-09-29 19:08:39.000000000 +0900
@@ -77,7 +77,7 @@ next:

*bh = NULL;
iblock = *pos >> sb->s_blocksize_bits;
- err = fat_bmap(dir, iblock, &phys, &mapped_blocks);
+ err = fat_bmap(dir, iblock, &phys, &mapped_blocks, 0);
if (err || !phys)
return -1; /* beyond EOF or error */

diff -puN fs/fat/fat.h~fat-mmu_private-race-fix fs/fat/fat.h
--- linux-2.6/fs/fat/fat.h~fat-mmu_private-race-fix 2008-09-29 13:58:53.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/fat.h 2008-09-29 19:14:24.000000000 +0900
@@ -91,7 +91,9 @@ struct msdos_inode_info {
/* for avoiding the race between fat_free() and fat_get_cluster() */
unsigned int cache_valid_id;

- loff_t mmu_private;
+ /* NOTE: mmu_private is 64bits, so must hold ->i_mutex to access */
+ loff_t mmu_private; /* physically allocated size */
+
int i_start; /* first cluster or 0 */
int i_logstart; /* logical first cluster */
int i_attrs; /* unused attribute bits */
@@ -222,7 +224,7 @@ extern void fat_cache_inval_inode(struct
extern int fat_get_cluster(struct inode *inode, int cluster,
int *fclus, int *dclus);
extern int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
- unsigned long *mapped_blocks);
+ unsigned long *mapped_blocks, int create);

/* fat/dir.c */
extern const struct file_operations fat_dir_operations;
diff -puN fs/fat/inode.c~fat-mmu_private-race-fix fs/fat/inode.c
--- linux-2.6/fs/fat/inode.c~fat-mmu_private-race-fix 2008-09-29 13:58:53.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/inode.c 2008-09-29 19:08:40.000000000 +0900
@@ -64,7 +64,7 @@ static inline int __fat_get_block(struct
sector_t phys;
int err, offset;

- err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
+ err = fat_bmap(inode, iblock, &phys, &mapped_blocks, create);
if (err)
return err;
if (phys) {
@@ -94,7 +94,7 @@ static inline int __fat_get_block(struct
*max_blocks = min(mapped_blocks, *max_blocks);
MSDOS_I(inode)->mmu_private += *max_blocks << sb->s_blocksize_bits;

- err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
+ err = fat_bmap(inode, iblock, &phys, &mapped_blocks, create);
if (err)
return err;

_

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