ext4: fix potential race between online resizing and write operations
commit 1d0c3924a92e69bfa91163bda83c12a994b4d106 upstream.
During an online resize an array of pointers to buffer heads gets
replaced so it can get enlarged. If there is a racing block
allocation or deallocation which uses the old array, and the old array
has gotten reused this can lead to a GPF or some other random kernel
memory getting modified.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206443
Link: https://lore.kernel.org/r/20200221053458.730016-2-tytso@mit.edu
Reported-by: Suraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org # 4.4.x
Cc: stable@kernel.org # 4.9.x
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 2455fe1..de601f3 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -279,6 +279,7 @@
ext4_group_t ngroups = ext4_get_groups_count(sb);
struct ext4_group_desc *desc;
struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct buffer_head *bh_p;
if (block_group >= ngroups) {
ext4_error(sb, "block_group >= groups_count - block_group = %u,"
@@ -289,7 +290,14 @@
group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
- if (!sbi->s_group_desc[group_desc]) {
+ bh_p = sbi_array_rcu_deref(sbi, s_group_desc, group_desc);
+ /*
+ * sbi_array_rcu_deref returns with rcu unlocked, this is ok since
+ * the pointer being dereferenced won't be dereferenced again. By
+ * looking at the usage in add_new_gdb() the value isn't modified,
+ * just the pointer, and so it remains valid.
+ */
+ if (!bh_p) {
ext4_error(sb, "Group descriptor not loaded - "
"block_group = %u, group_desc = %u, desc = %u",
block_group, group_desc, offset);
@@ -297,10 +305,10 @@
}
desc = (struct ext4_group_desc *)(
- (__u8 *)sbi->s_group_desc[group_desc]->b_data +
+ (__u8 *)bh_p->b_data +
offset * EXT4_DESC_SIZE(sb));
if (bh)
- *bh = sbi->s_group_desc[group_desc];
+ *bh = bh_p;
return desc;
}
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9713d3d..42c6c02 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1367,7 +1367,7 @@
loff_t s_bitmap_maxbytes; /* max bytes for bitmap files */
struct buffer_head * s_sbh; /* Buffer containing the super block */
struct ext4_super_block *s_es; /* Pointer to the super block in the buffer */
- struct buffer_head **s_group_desc;
+ struct buffer_head * __rcu *s_group_desc;
unsigned int s_mount_opt;
unsigned int s_mount_opt2;
unsigned int s_mount_flags;
@@ -1550,6 +1550,23 @@
}
/*
+ * Returns: sbi->field[index]
+ * Used to access an array element from the following sbi fields which require
+ * rcu protection to avoid dereferencing an invalid pointer due to reassignment
+ * - s_group_desc
+ * - s_group_info
+ * - s_flex_group
+ */
+#define sbi_array_rcu_deref(sbi, field, index) \
+({ \
+ typeof(*((sbi)->field)) _v; \
+ rcu_read_lock(); \
+ _v = ((typeof(_v)*)rcu_dereference((sbi)->field))[index]; \
+ rcu_read_unlock(); \
+ _v; \
+})
+
+/*
* Inode dynamic state flags
*/
enum {
@@ -2558,6 +2575,7 @@
extern bool ext4_empty_dir(struct inode *inode);
/* resize.c */
+extern void ext4_kvfree_array_rcu(void *to_free);
extern int ext4_group_add(struct super_block *sb,
struct ext4_new_group_data *input);
extern int ext4_group_extend(struct super_block *sb,
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index aef2a24..b788bbe 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -16,6 +16,33 @@
#include "ext4_jbd2.h"
+struct ext4_rcu_ptr {
+ struct rcu_head rcu;
+ void *ptr;
+};
+
+static void ext4_rcu_ptr_callback(struct rcu_head *head)
+{
+ struct ext4_rcu_ptr *ptr;
+
+ ptr = container_of(head, struct ext4_rcu_ptr, rcu);
+ kvfree(ptr->ptr);
+ kfree(ptr);
+}
+
+void ext4_kvfree_array_rcu(void *to_free)
+{
+ struct ext4_rcu_ptr *ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
+
+ if (ptr) {
+ ptr->ptr = to_free;
+ call_rcu(&ptr->rcu, ext4_rcu_ptr_callback);
+ return;
+ }
+ synchronize_rcu();
+ kvfree(to_free);
+}
+
int ext4_resize_begin(struct super_block *sb)
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -541,8 +568,8 @@
brelse(gdb);
goto out;
}
- memcpy(gdb->b_data, sbi->s_group_desc[j]->b_data,
- gdb->b_size);
+ memcpy(gdb->b_data, sbi_array_rcu_deref(sbi,
+ s_group_desc, j)->b_data, gdb->b_size);
set_buffer_uptodate(gdb);
err = ext4_handle_dirty_metadata(handle, NULL, gdb);
@@ -849,13 +876,15 @@
}
brelse(dind);
- o_group_desc = EXT4_SB(sb)->s_group_desc;
+ rcu_read_lock();
+ o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+ rcu_read_unlock();
n_group_desc[gdb_num] = gdb_bh;
- EXT4_SB(sb)->s_group_desc = n_group_desc;
+ rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
EXT4_SB(sb)->s_gdb_count++;
- kvfree(o_group_desc);
+ ext4_kvfree_array_rcu(o_group_desc);
le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
err = ext4_handle_dirty_super(handle, sb);
@@ -903,9 +932,11 @@
return err;
}
- o_group_desc = EXT4_SB(sb)->s_group_desc;
+ rcu_read_lock();
+ o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
memcpy(n_group_desc, o_group_desc,
EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+ rcu_read_unlock();
n_group_desc[gdb_num] = gdb_bh;
BUFFER_TRACE(gdb_bh, "get_write_access");
@@ -916,9 +947,9 @@
return err;
}
- EXT4_SB(sb)->s_group_desc = n_group_desc;
+ rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
EXT4_SB(sb)->s_gdb_count++;
- kvfree(o_group_desc);
+ ext4_kvfree_array_rcu(o_group_desc);
return err;
}
@@ -1180,7 +1211,8 @@
* use non-sparse filesystems anymore. This is already checked above.
*/
if (gdb_off) {
- gdb_bh = sbi->s_group_desc[gdb_num];
+ gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+ gdb_num);
BUFFER_TRACE(gdb_bh, "get_write_access");
err = ext4_journal_get_write_access(handle, gdb_bh);
@@ -1262,7 +1294,7 @@
/*
* get_write_access() has been called on gdb_bh by ext4_add_new_desc().
*/
- gdb_bh = sbi->s_group_desc[gdb_num];
+ gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc, gdb_num);
/* Update group descriptor block for new group */
gdp = (struct ext4_group_desc *)(gdb_bh->b_data +
gdb_off * EXT4_DESC_SIZE(sb));
@@ -1489,7 +1521,8 @@
for (; gdb_num <= gdb_num_end; gdb_num++) {
struct buffer_head *gdb_bh;
- gdb_bh = sbi->s_group_desc[gdb_num];
+ gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+ gdb_num);
if (old_gdb == gdb_bh->b_blocknr)
continue;
update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b69a78c..75840ee 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -826,6 +826,7 @@
{
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_super_block *es = sbi->s_es;
+ struct buffer_head **group_desc;
int aborted = 0;
int i, err;
@@ -857,9 +858,12 @@
if (!(sb->s_flags & MS_RDONLY))
ext4_commit_super(sb, 1);
+ rcu_read_lock();
+ group_desc = rcu_dereference(sbi->s_group_desc);
for (i = 0; i < sbi->s_gdb_count; i++)
- brelse(sbi->s_group_desc[i]);
- kvfree(sbi->s_group_desc);
+ brelse(group_desc[i]);
+ kvfree(group_desc);
+ rcu_read_unlock();
kvfree(sbi->s_flex_groups);
percpu_counter_destroy(&sbi->s_freeclusters_counter);
percpu_counter_destroy(&sbi->s_freeinodes_counter);
@@ -3403,7 +3407,7 @@
static int ext4_fill_super(struct super_block *sb, void *data, int silent)
{
char *orig_data = kstrdup(data, GFP_KERNEL);
- struct buffer_head *bh;
+ struct buffer_head *bh, **group_desc;
struct ext4_super_block *es = NULL;
struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
ext4_fsblk_t block;
@@ -3955,9 +3959,10 @@
goto failed_mount;
}
}
- sbi->s_group_desc = ext4_kvmalloc(db_count *
+ rcu_assign_pointer(sbi->s_group_desc,
+ ext4_kvmalloc(db_count *
sizeof(struct buffer_head *),
- GFP_KERNEL);
+ GFP_KERNEL));
if (sbi->s_group_desc == NULL) {
ext4_msg(sb, KERN_ERR, "not enough memory");
ret = -ENOMEM;
@@ -3967,14 +3972,19 @@
bgl_lock_init(sbi->s_blockgroup_lock);
for (i = 0; i < db_count; i++) {
+ struct buffer_head *bh;
+
block = descriptor_loc(sb, logical_sb_block, i);
- sbi->s_group_desc[i] = sb_bread_unmovable(sb, block);
- if (!sbi->s_group_desc[i]) {
+ bh = sb_bread_unmovable(sb, block);
+ if (!bh) {
ext4_msg(sb, KERN_ERR,
"can't read group descriptor %d", i);
db_count = i;
goto failed_mount2;
}
+ rcu_read_lock();
+ rcu_dereference(sbi->s_group_desc)[i] = bh;
+ rcu_read_unlock();
}
sbi->s_gdb_count = db_count;
if (!ext4_check_descriptors(sb, logical_sb_block, &first_not_zeroed)) {
@@ -4349,9 +4359,12 @@
if (sbi->s_mmp_tsk)
kthread_stop(sbi->s_mmp_tsk);
failed_mount2:
+ rcu_read_lock();
+ group_desc = rcu_dereference(sbi->s_group_desc);
for (i = 0; i < db_count; i++)
- brelse(sbi->s_group_desc[i]);
- kvfree(sbi->s_group_desc);
+ brelse(group_desc[i]);
+ kvfree(group_desc);
+ rcu_read_unlock();
failed_mount:
if (sbi->s_chksum_driver)
crypto_free_shash(sbi->s_chksum_driver);