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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index c0253d82e9a50b91797210c799348a15a0c17827..ae73636a0f9b04fc7c1f3c5efc8b8ac34de7bd10 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1513,7 +1513,7 @@ 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 8ca4a23129aafd389f0a6a126e25d3640b38dd37..7db0c8814f2ec85108e37c7ceaf6fff03c30d200 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -325,11 +325,13 @@ 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);
@@ -365,12 +367,13 @@ 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;
        }
 
@@ -1051,7 +1054,8 @@ 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)) {
@@ -1074,7 +1078,8 @@ 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 954605e29761ed3739433ac5aedff3ecf70434c1..c76ffc259d197a76bd7201c28be47d2d1114c6c8 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3038,7 +3038,8 @@ 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);
@@ -4932,7 +4933,8 @@ 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);
        }
 
        /*
@@ -5089,7 +5091,8 @@ 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(clusters_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 34d0e3c8e49e19eb70d75ec7eb5cbdfe85293d9e..f178af1dffe07d72595948ffb2fee3392e8cd838 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1432,11 +1432,14 @@ 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 cbd3ae3c91dcdf7b7012daf1765b5269cfcfe153..531ea4f39bb27ac9267557fb1f93c77f37a916eb 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -971,6 +971,7 @@ 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;
 
@@ -1006,8 +1007,13 @@ 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);
@@ -2339,8 +2345,8 @@ 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;
@@ -2349,22 +2355,37 @@ 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;
 }
 
@@ -2372,6 +2393,7 @@ 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;
 
@@ -2389,12 +2411,11 @@ 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;
@@ -3596,6 +3617,7 @@ 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;
@@ -4647,8 +4669,14 @@ 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);