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Date: Tue, 18 Feb 2020 19:08:50 -0800
From: Suraj Jitindar Singh <surajjs@...zon.com>
To: <linux-ext4@...r.kernel.org>
CC: <tytso@....edu>, <sblbir@...zon.com>, <sjitindarsingh@...il.com>,
"Suraj Jitindar Singh" <surajjs@...zon.com>,
<stable@...r.kernel.org>
Subject: [PATCH 2/3] ext4: fix potential race between s_group_info online resizing and access
During an online resize an array of pointers to s_group_info gets replaced
so it can get enlarged. If there is a concurrent access to the array in
ext4_get_group_info() and this memory has been reused then this can lead to
an invalid memory access.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206443
Signed-off-by: Suraj Jitindar Singh <surajjs@...zon.com>
Cc: stable@...r.kernel.org
---
fs/ext4/ext4.h | 6 +++---
fs/ext4/mballoc.c | 10 ++++++----
2 files changed, 9 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 236fc6500340..3f4aaaae7da6 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2994,13 +2994,13 @@ static inline
struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
ext4_group_t group)
{
- struct ext4_group_info ***grp_info;
+ struct ext4_group_info **grp_info;
long indexv, indexh;
BUG_ON(group >= EXT4_SB(sb)->s_groups_count);
- grp_info = EXT4_SB(sb)->s_group_info;
indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
- return grp_info[indexv][indexh];
+ grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
+ return grp_info[indexh];
}
/*
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index f64838187559..0d9b17afc85f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2356,7 +2356,7 @@ int ext4_mb_alloc_groupinfo(struct super_block *sb, ext4_group_t ngroups)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
unsigned size;
- struct ext4_group_info ***new_groupinfo;
+ struct ext4_group_info ***old_groupinfo, ***new_groupinfo;
size = (ngroups + EXT4_DESC_PER_BLOCK(sb) - 1) >>
EXT4_DESC_PER_BLOCK_BITS(sb);
@@ -2369,13 +2369,15 @@ int ext4_mb_alloc_groupinfo(struct super_block *sb, ext4_group_t ngroups)
ext4_msg(sb, KERN_ERR, "can't allocate buddy meta group");
return -ENOMEM;
}
- if (sbi->s_group_info) {
+ old_groupinfo = sbi->s_group_info;
+ if (sbi->s_group_info)
memcpy(new_groupinfo, sbi->s_group_info,
sbi->s_group_info_size * sizeof(*sbi->s_group_info));
- kvfree(sbi->s_group_info);
- }
sbi->s_group_info = new_groupinfo;
+ rcu_assign_pointer(sbi->s_group_info, new_groupinfo);
sbi->s_group_info_size = size / sizeof(*sbi->s_group_info);
+ if (old_groupinfo)
+ ext4_kvfree_array_rcu(old_groupinfo);
ext4_debug("allocated s_groupinfo array for %d meta_bg's\n",
sbi->s_group_info_size);
return 0;
--
2.17.1
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