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: Suraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Balbir Singh <sblbir@amazon.com>
Cc: stable@kernel.org

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index b51003f..b1ece53 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -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];
 }
 
 /*

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index f648381..1b46fb6 100644 (file)
--- 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 +2369,16 @@ 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);