ext4: fix potential race between s_flex_groups online resizing and access

commit 7c990728b99ed6fbe9c75fc202fce1172d9916da upstream.

During an online resize an array of s_flex_groups structures gets replaced
so it can get enlarged. If there is a concurrent access to the array and
this memory has been reused then this can lead to an invalid memory access.

The s_flex_group array has been converted into an array of pointers rather
than an array of structures. This is to ensure that the information
contained in the structures cannot get out of sync during a resize due to
an accessor updating the value in the old structure after it has been
copied but before the array pointer is updated. Since the structures them-
selves are no longer copied but only the pointers to them this case is
mitigated.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206443
Link: https://lore.kernel.org/r/20200221053458.730016-4-tytso@mit.edu
Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org # 4.14.x
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 94f4f6d55c1a49de6c928410f4236e87f446e6ba..8b55abdd7249a10657ba6d1a38895c42b68612f5 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1492,7 +1492,7 @@ struct ext4_sb_info {
        unsigned int s_extent_max_zeroout_kb;
 
        unsigned int s_log_groups_per_flex;
-       struct flex_groups *s_flex_groups;
+       struct flex_groups * __rcu *s_flex_groups;
        ext4_group_t s_flex_groups_allocated;
 
        /* workqueue for reserved extent conversions (buffered io) */

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 2f46564d3fca98c228522fa97b2ff0336483677a..2a480c0ef1bc11f07aa500d9dc3a683a6d35078f 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -333,11 +333,13 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
 
        percpu_counter_inc(&sbi->s_freeinodes_counter);
        if (sbi->s_log_groups_per_flex) {
-               ext4_group_t f = ext4_flex_group(sbi, block_group);
+               struct flex_groups *fg;
 
-               atomic_inc(&sbi->s_flex_groups[f].free_inodes);
+               fg = sbi_array_rcu_deref(sbi, s_flex_groups,
+                                        ext4_flex_group(sbi, block_group));
+               atomic_inc(&fg->free_inodes);
                if (is_directory)
-                       atomic_dec(&sbi->s_flex_groups[f].used_dirs);
+                       atomic_dec(&fg->used_dirs);
        }
        BUFFER_TRACE(bh2, "call ext4_handle_dirty_metadata");
        fatal = ext4_handle_dirty_metadata(handle, NULL, bh2);
@@ -378,12 +380,13 @@ static void get_orlov_stats(struct super_block *sb, ext4_group_t g,
                            int flex_size, struct orlov_stats *stats)
 {
        struct ext4_group_desc *desc;
-       struct flex_groups *flex_group = EXT4_SB(sb)->s_flex_groups;
 
        if (flex_size > 1) {
-               stats->free_inodes = atomic_read(&flex_group[g].free_inodes);
-               stats->free_clusters = atomic64_read(&flex_group[g].free_clusters);
-               stats->used_dirs = atomic_read(&flex_group[g].used_dirs);
+               struct flex_groups *fg = sbi_array_rcu_deref(EXT4_SB(sb),
+                                                            s_flex_groups, g);
+               stats->free_inodes = atomic_read(&fg->free_inodes);
+               stats->free_clusters = atomic64_read(&fg->free_clusters);
+               stats->used_dirs = atomic_read(&fg->used_dirs);
                return;
        }
 
@@ -1062,7 +1065,8 @@ got:
                if (sbi->s_log_groups_per_flex) {
                        ext4_group_t f = ext4_flex_group(sbi, group);
 
-                       atomic_inc(&sbi->s_flex_groups[f].used_dirs);
+                       atomic_inc(&sbi_array_rcu_deref(sbi, s_flex_groups,
+                                                       f)->used_dirs);
                }
        }
        if (ext4_has_group_desc_csum(sb)) {
@@ -1085,7 +1089,8 @@ got:
 
        if (sbi->s_log_groups_per_flex) {
                flex_group = ext4_flex_group(sbi, group);
-               atomic_dec(&sbi->s_flex_groups[flex_group].free_inodes);
+               atomic_dec(&sbi_array_rcu_deref(sbi, s_flex_groups,
+                                               flex_group)->free_inodes);
        }
 
        inode->i_ino = ino + group * EXT4_INODES_PER_GROUP(sb);

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 3ba9a4ae4eacdd079684386658884e196ca7daad..fb865216edb9bd06393cf59fee23969d16988b52 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3052,7 +3052,8 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                ext4_group_t flex_group = ext4_flex_group(sbi,
                                                          ac->ac_b_ex.fe_group);
                atomic64_sub(ac->ac_b_ex.fe_len,
-                            &sbi->s_flex_groups[flex_group].free_clusters);
+                            &sbi_array_rcu_deref(sbi, s_flex_groups,
+                                                 flex_group)->free_clusters);
        }
 
        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
@@ -4947,7 +4948,8 @@ do_more:
        if (sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
                atomic64_add(count_clusters,
-                            &sbi->s_flex_groups[flex_group].free_clusters);
+                            &sbi_array_rcu_deref(sbi, s_flex_groups,
+                                                 flex_group)->free_clusters);
        }
 
        if (!(flags & EXT4_FREE_BLOCKS_NO_QUOT_UPDATE))
@@ -5092,7 +5094,8 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
        if (sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
                atomic64_add(EXT4_NUM_B2C(sbi, blocks_freed),
-                            &sbi->s_flex_groups[flex_group].free_clusters);
+                            &sbi_array_rcu_deref(sbi, s_flex_groups,
+                                                 flex_group)->free_clusters);
        }
 
        ext4_mb_unload_buddy(&e4b);

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 16e3830da5487438175a77873c3571f63dd850fd..d42f7471fd5b8c1f5e47910d93ad1080dade630d 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1425,11 +1425,14 @@ static void ext4_update_super(struct super_block *sb,
                   percpu_counter_read(&sbi->s_freeclusters_counter));
        if (ext4_has_feature_flex_bg(sb) && sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group;
+               struct flex_groups *fg;
+
                flex_group = ext4_flex_group(sbi, group_data[0].group);
+               fg = sbi_array_rcu_deref(sbi, s_flex_groups, flex_group);
                atomic64_add(EXT4_NUM_B2C(sbi, free_blocks),
-                            &sbi->s_flex_groups[flex_group].free_clusters);
+                            &fg->free_clusters);
                atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count,
-                          &sbi->s_flex_groups[flex_group].free_inodes);
+                          &fg->free_inodes);
        }
 
        /*

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b14a0c5638e701ccd8116638051a346da4621a44..f1c1c180d267160dff90c65750979a2558f82039 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -901,6 +901,7 @@ static void ext4_put_super(struct super_block *sb)
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        struct buffer_head **group_desc;
+       struct flex_groups **flex_groups;
        int aborted = 0;
        int i, err;
 
@@ -937,8 +938,13 @@ static void ext4_put_super(struct super_block *sb)
        for (i = 0; i < sbi->s_gdb_count; i++)
                brelse(group_desc[i]);
        kvfree(group_desc);
+       flex_groups = rcu_dereference(sbi->s_flex_groups);
+       if (flex_groups) {
+               for (i = 0; i < sbi->s_flex_groups_allocated; i++)
+                       kvfree(flex_groups[i]);
+               kvfree(flex_groups);
+       }
        rcu_read_unlock();
-       kvfree(sbi->s_flex_groups);
        percpu_counter_destroy(&sbi->s_freeclusters_counter);
        percpu_counter_destroy(&sbi->s_freeinodes_counter);
        percpu_counter_destroy(&sbi->s_dirs_counter);
@@ -2231,8 +2237,8 @@ done:
 int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);
-       struct flex_groups *new_groups;
-       int size;
+       struct flex_groups **old_groups, **new_groups;
+       int size, i;
 
        if (!sbi->s_log_groups_per_flex)
                return 0;
@@ -2241,22 +2247,37 @@ int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
        if (size <= sbi->s_flex_groups_allocated)
                return 0;
 
-       size = roundup_pow_of_two(size * sizeof(struct flex_groups));
-       new_groups = kvzalloc(size, GFP_KERNEL);
+       new_groups = kvzalloc(roundup_pow_of_two(size *
+                             sizeof(*sbi->s_flex_groups)), GFP_KERNEL);
        if (!new_groups) {
-               ext4_msg(sb, KERN_ERR, "not enough memory for %d flex groups",
-                        size / (int) sizeof(struct flex_groups));
+               ext4_msg(sb, KERN_ERR,
+                        "not enough memory for %d flex group pointers", size);
                return -ENOMEM;
        }
-
-       if (sbi->s_flex_groups) {
-               memcpy(new_groups, sbi->s_flex_groups,
-                      (sbi->s_flex_groups_allocated *
-                       sizeof(struct flex_groups)));
-               kvfree(sbi->s_flex_groups);
+       for (i = sbi->s_flex_groups_allocated; i < size; i++) {
+               new_groups[i] = kvzalloc(roundup_pow_of_two(
+                                        sizeof(struct flex_groups)),
+                                        GFP_KERNEL);
+               if (!new_groups[i]) {
+                       for (i--; i >= sbi->s_flex_groups_allocated; i--)
+                               kvfree(new_groups[i]);
+                       kvfree(new_groups);
+                       ext4_msg(sb, KERN_ERR,
+                                "not enough memory for %d flex groups", size);
+                       return -ENOMEM;
+               }
        }
-       sbi->s_flex_groups = new_groups;
-       sbi->s_flex_groups_allocated = size / sizeof(struct flex_groups);
+       rcu_read_lock();
+       old_groups = rcu_dereference(sbi->s_flex_groups);
+       if (old_groups)
+               memcpy(new_groups, old_groups,
+                      (sbi->s_flex_groups_allocated *
+                       sizeof(struct flex_groups *)));
+       rcu_read_unlock();
+       rcu_assign_pointer(sbi->s_flex_groups, new_groups);
+       sbi->s_flex_groups_allocated = size;
+       if (old_groups)
+               ext4_kvfree_array_rcu(old_groups);
        return 0;
 }
 
@@ -2264,6 +2285,7 @@ static int ext4_fill_flex_info(struct super_block *sb)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_group_desc *gdp = NULL;
+       struct flex_groups *fg;
        ext4_group_t flex_group;
        int i, err;
 
@@ -2281,12 +2303,11 @@ static int ext4_fill_flex_info(struct super_block *sb)
                gdp = ext4_get_group_desc(sb, i, NULL);
 
                flex_group = ext4_flex_group(sbi, i);
-               atomic_add(ext4_free_inodes_count(sb, gdp),
-                          &sbi->s_flex_groups[flex_group].free_inodes);
+               fg = sbi_array_rcu_deref(sbi, s_flex_groups, flex_group);
+               atomic_add(ext4_free_inodes_count(sb, gdp), &fg->free_inodes);
                atomic64_add(ext4_free_group_clusters(sb, gdp),
-                            &sbi->s_flex_groups[flex_group].free_clusters);
-               atomic_add(ext4_used_dirs_count(sb, gdp),
-                          &sbi->s_flex_groups[flex_group].used_dirs);
+                            &fg->free_clusters);
+               atomic_add(ext4_used_dirs_count(sb, gdp), &fg->used_dirs);
        }
 
        return 1;
@@ -3496,6 +3517,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        struct buffer_head *bh, **group_desc;
        struct ext4_super_block *es = NULL;
        struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
+       struct flex_groups **flex_groups;
        ext4_fsblk_t block;
        ext4_fsblk_t sb_block = get_sb_block(&data);
        ext4_fsblk_t logical_sb_block;
@@ -4494,8 +4516,14 @@ failed_mount7:
        ext4_unregister_li_request(sb);
 failed_mount6:
        ext4_mb_release(sb);
-       if (sbi->s_flex_groups)
-               kvfree(sbi->s_flex_groups);
+       rcu_read_lock();
+       flex_groups = rcu_dereference(sbi->s_flex_groups);
+       if (flex_groups) {
+               for (i = 0; i < sbi->s_flex_groups_allocated; i++)
+                       kvfree(flex_groups[i]);
+               kvfree(flex_groups);
+       }
+       rcu_read_unlock();
        percpu_counter_destroy(&sbi->s_freeclusters_counter);
        percpu_counter_destroy(&sbi->s_freeinodes_counter);
        percpu_counter_destroy(&sbi->s_dirs_counter);