From: Dmitry Monakhov <dmonakhov@openvz.org>
To: linux-ext4@vger.kernel.org
Cc: tytso@mit.edu, Dmitry Monakhov <dmonakhov@openvz.org>
Subject: [PATCH 1/4] ext4: fix potential use after free during resize V2
Date: Tue, 2 Dec 2014 15:00:51 +0400 [thread overview]
Message-ID: <1417518054-21733-1-git-send-email-dmonakhov@openvz.org> (raw)
We need some sort of synchronization while updating ->s_group_desc
because there are a lot of users which can access old ->s_group_desc
array after it was released.
changes from V1:
- use RCU instead seqcount
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
fs/ext4/balloc.c | 12 ++++++++----
fs/ext4/resize.c | 6 ++++--
2 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 83a6f49..2d0a0de 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -282,6 +282,7 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
unsigned int offset;
ext4_group_t ngroups = ext4_get_groups_count(sb);
struct ext4_group_desc *desc;
+ struct buffer_head *gd_bh;
struct ext4_sb_info *sbi = EXT4_SB(sb);
if (block_group >= ngroups) {
@@ -293,7 +294,10 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
- if (!sbi->s_group_desc[group_desc]) {
+ rcu_read_lock();
+ gd_bh = *rcu_dereference(sbi->s_group_desc) + group_desc;
+ rcu_read_unlock();
+ if (!gd_bh) {
ext4_error(sb, "Group descriptor not loaded - "
"block_group = %u, group_desc = %u, desc = %u",
block_group, group_desc, offset);
@@ -301,10 +305,10 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
}
desc = (struct ext4_group_desc *)(
- (__u8 *)sbi->s_group_desc[group_desc]->b_data +
- offset * EXT4_DESC_SIZE(sb));
+ (__u8 *)gd_bh->b_data + offset * EXT4_DESC_SIZE(sb));
if (bh)
- *bh = sbi->s_group_desc[group_desc];
+ *bh = gd_bh;
+
return desc;
}
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index bf76f40..08c2256 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -854,8 +854,9 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
n_group_desc[gdb_num] = gdb_bh;
- EXT4_SB(sb)->s_group_desc = n_group_desc;
EXT4_SB(sb)->s_gdb_count++;
+ rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
+ synchronize_rcu();
kvfree(o_group_desc);
le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
@@ -907,8 +908,9 @@ static int add_new_gdb_meta_bg(struct super_block *sb,
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
n_group_desc[gdb_num] = gdb_bh;
- EXT4_SB(sb)->s_group_desc = n_group_desc;
EXT4_SB(sb)->s_gdb_count++;
+ rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
+ synchronize_rcu();
kvfree(o_group_desc);
BUFFER_TRACE(gdb_bh, "get_write_access");
err = ext4_journal_get_write_access(handle, gdb_bh);
--
1.7.1
next reply other threads:[~2014-12-02 11:01 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-02 11:00 Dmitry Monakhov [this message]
2014-12-02 11:00 ` [PATCH 2/4] ext4: prevent fsreentrance deadlock for inline_data Dmitry Monakhov
2014-12-02 23:07 ` Theodore Ts'o
2014-12-02 11:00 ` [PATCH 3/4] ext4: ext4_inline_data_fiemap should respect callers argument Dmitry Monakhov
2014-12-02 23:07 ` Theodore Ts'o
2014-12-02 11:00 ` [PATCH 4/4] ext4: fix suboptimal seek_{data,hole} extents traversial Dmitry Monakhov
2014-12-02 23:07 ` Theodore Ts'o
2014-12-11 20:05 ` Theodore Ts'o
2014-12-12 8:52 ` Dmitry Monakhov
2014-12-17 3:57 ` Theodore Ts'o
2014-12-17 15:06 ` Dmitry Monakhov
2014-12-18 2:39 ` Theodore Ts'o
2014-12-27 15:39 ` Theodore Ts'o
2014-12-28 18:55 ` Dmitry Monakhov
2014-12-29 4:13 ` Theodore Ts'o
2015-01-02 20:03 ` Theodore Ts'o
2015-01-03 19:16 ` Dmitry Monakhov
2014-12-02 11:12 ` [PATCH 1/4] ext4: fix potential use after free during resize V2 Dmitry Monakhov
2014-12-02 23:06 ` Theodore Ts'o
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