Commit df3da4ea authored by Suraj Jitindar Singh's avatar Suraj Jitindar Singh Committed by Theodore Ts'o
Browse files

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
Link: https://lore.kernel.org/r/20200221053458.730016-3-tytso@mit.edu


Signed-off-by: default avatarSuraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarBalbir Singh <sblbir@amazon.com>
Cc: stable@kernel.org
parent 1d0c3924

fs/ext4/ext4.h

+4 −4
Original line number Diff line number Diff line
@@ -1462,7 +1462,7 @@ struct ext4_sb_info { 
#endif



	/* for buddy allocator */

	struct ext4_group_info ***s_group_info;

	struct ext4_group_info ** __rcu *s_group_info;

	struct inode *s_buddy_cache;

	spinlock_t s_md_lock;

	unsigned short *s_mb_offsets;
@@ -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];

}



/*

fs/ext4/mballoc.c

+35 −17
Original line number Diff line number Diff line
@@ -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 +2369,16 @@ 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) {

		memcpy(new_groupinfo, sbi->s_group_info,

	rcu_read_lock();

	old_groupinfo = rcu_dereference(sbi->s_group_info);

	if (old_groupinfo)

		memcpy(new_groupinfo, old_groupinfo,

		       sbi->s_group_info_size * sizeof(*sbi->s_group_info));

		kvfree(sbi->s_group_info);

	}

	sbi->s_group_info = new_groupinfo;

	rcu_read_unlock();

	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;
@@ -2387,6 +2390,7 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group, 
{

	int i;

	int metalen = 0;

	int idx = group >> EXT4_DESC_PER_BLOCK_BITS(sb);

	struct ext4_sb_info *sbi = EXT4_SB(sb);

	struct ext4_group_info **meta_group_info;

	struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);
@@ -2405,12 +2409,12 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group, 
				 "for a buddy group");

			goto exit_meta_group_info;

		}

		sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)] =

			meta_group_info;

		rcu_read_lock();

		rcu_dereference(sbi->s_group_info)[idx] = meta_group_info;

		rcu_read_unlock();

	}



	meta_group_info =

		sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)];

	meta_group_info = sbi_array_rcu_deref(sbi, s_group_info, idx);

	i = group & (EXT4_DESC_PER_BLOCK(sb) - 1);



	meta_group_info[i] = kmem_cache_zalloc(cachep, GFP_NOFS);
@@ -2458,8 +2462,13 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group, 
exit_group_info:

	/* If a meta_group_info table has been allocated, release it now */

	if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {

		kfree(sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)]);

		sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)] = NULL;

		struct ext4_group_info ***group_info;



		rcu_read_lock();

		group_info = rcu_dereference(sbi->s_group_info);

		kfree(group_info[idx]);

		group_info[idx] = NULL;

		rcu_read_unlock();

	}

exit_meta_group_info:

	return -ENOMEM;
@@ -2472,6 +2481,7 @@ static int ext4_mb_init_backend(struct super_block *sb) 
	struct ext4_sb_info *sbi = EXT4_SB(sb);

	int err;

	struct ext4_group_desc *desc;

	struct ext4_group_info ***group_info;

	struct kmem_cache *cachep;



	err = ext4_mb_alloc_groupinfo(sb, ngroups);
@@ -2507,11 +2517,16 @@ err_freebuddy: 
	while (i-- > 0)

		kmem_cache_free(cachep, ext4_get_group_info(sb, i));

	i = sbi->s_group_info_size;

	rcu_read_lock();

	group_info = rcu_dereference(sbi->s_group_info);

	while (i-- > 0)

		kfree(sbi->s_group_info[i]);

		kfree(group_info[i]);

	rcu_read_unlock();

	iput(sbi->s_buddy_cache);

err_freesgi:

	kvfree(sbi->s_group_info);

	rcu_read_lock();

	kvfree(rcu_dereference(sbi->s_group_info));

	rcu_read_unlock();

	return -ENOMEM;

}
@@ -2700,7 +2715,7 @@ int ext4_mb_release(struct super_block *sb) 
	ext4_group_t ngroups = ext4_get_groups_count(sb);

	ext4_group_t i;

	int num_meta_group_infos;

	struct ext4_group_info *grinfo;

	struct ext4_group_info *grinfo, ***group_info;

	struct ext4_sb_info *sbi = EXT4_SB(sb);

	struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);
@@ -2719,9 +2734,12 @@ int ext4_mb_release(struct super_block *sb) 
		num_meta_group_infos = (ngroups +

				EXT4_DESC_PER_BLOCK(sb) - 1) >>

			EXT4_DESC_PER_BLOCK_BITS(sb);

		rcu_read_lock();

		group_info = rcu_dereference(sbi->s_group_info);

		for (i = 0; i < num_meta_group_infos; i++)

			kfree(sbi->s_group_info[i]);

		kvfree(sbi->s_group_info);

			kfree(group_info[i]);

		kvfree(group_info);

		rcu_read_unlock();

	}

	kfree(sbi->s_mb_offsets);

	kfree(sbi->s_mb_maxs);

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