On Tue, 2020-02-18 at 19:08 -0800, Suraj Jitindar Singh wrote:

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@amazon.com Cc: stable@vger.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;

Reviewed-by: Balbir Singh sblbir@amazon.com