[PATCH 3.18 006/105] fat: validate ->i_start before using

From: Greg Kroah-Hartman
Date: Mon Sep 24 2018 - 07:37:55 EST


3.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>

[ Upstream commit 0afa9626667c3659ef8bd82d42a11e39fedf235c ]

On corrupted FATfs may have invalid ->i_start. To handle it, this checks
->i_start before using, and return proper error code.

Link: http://lkml.kernel.org/r/87o9f8y1t5.fsf_-_@xxxxxxxxxxxxxxxxxx
Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@xxxxxxxxx>
Tested-by: Anatoly Trosinenko <anatoly.trosinenko@xxxxxxxxx>
Cc: Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/fat/cache.c | 19 ++++++++++++-------
fs/fat/fat.h | 5 +++++
fs/fat/fatent.c | 6 +++---
3 files changed, 20 insertions(+), 10 deletions(-)

--- a/fs/fat/cache.c
+++ b/fs/fat/cache.c
@@ -226,7 +226,8 @@ static inline void cache_init(struct fat
int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
{
struct super_block *sb = inode->i_sb;
- const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
+ struct msdos_sb_info *sbi = MSDOS_SB(sb);
+ const int limit = sb->s_maxbytes >> sbi->cluster_bits;
struct fat_entry fatent;
struct fat_cache_id cid;
int nr;
@@ -235,6 +236,12 @@ int fat_get_cluster(struct inode *inode,

*fclus = 0;
*dclus = MSDOS_I(inode)->i_start;
+ if (!fat_valid_entry(sbi, *dclus)) {
+ fat_fs_error_ratelimit(sb,
+ "%s: invalid start cluster (i_pos %lld, start %08x)",
+ __func__, MSDOS_I(inode)->i_pos, *dclus);
+ return -EIO;
+ }
if (cluster == 0)
return 0;

@@ -251,9 +258,8 @@ int fat_get_cluster(struct inode *inode,
/* prevent the infinite loop of cluster chain */
if (*fclus > limit) {
fat_fs_error_ratelimit(sb,
- "%s: detected the cluster chain loop"
- " (i_pos %lld)", __func__,
- MSDOS_I(inode)->i_pos);
+ "%s: detected the cluster chain loop (i_pos %lld)",
+ __func__, MSDOS_I(inode)->i_pos);
nr = -EIO;
goto out;
}
@@ -263,9 +269,8 @@ int fat_get_cluster(struct inode *inode,
goto out;
else if (nr == FAT_ENT_FREE) {
fat_fs_error_ratelimit(sb,
- "%s: invalid cluster chain (i_pos %lld)",
- __func__,
- MSDOS_I(inode)->i_pos);
+ "%s: invalid cluster chain (i_pos %lld)",
+ __func__, MSDOS_I(inode)->i_pos);
nr = -EIO;
goto out;
} else if (nr == FAT_ENT_EOF) {
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -347,6 +347,11 @@ static inline void fatent_brelse(struct
fatent->fat_inode = NULL;
}

+static inline bool fat_valid_entry(struct msdos_sb_info *sbi, int entry)
+{
+ return FAT_START_ENT <= entry && entry < sbi->max_cluster;
+}
+
extern void fat_ent_access_init(struct super_block *sb);
extern int fat_ent_read(struct inode *inode, struct fat_entry *fatent,
int entry);
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -26,7 +26,7 @@ static void fat12_ent_blocknr(struct sup
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
int bytes = entry + (entry >> 1);
- WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
+ WARN_ON(!fat_valid_entry(sbi, entry));
*offset = bytes & (sb->s_blocksize - 1);
*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}
@@ -36,7 +36,7 @@ static void fat_ent_blocknr(struct super
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
int bytes = (entry << sbi->fatent_shift);
- WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
+ WARN_ON(!fat_valid_entry(sbi, entry));
*offset = bytes & (sb->s_blocksize - 1);
*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}
@@ -356,7 +356,7 @@ int fat_ent_read(struct inode *inode, st
int err, offset;
sector_t blocknr;

- if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
+ if (!fat_valid_entry(sbi, entry)) {
fatent_brelse(fatent);
fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
return -EIO;