Re: [External] [PATCH] erofs: fix use-after-free of fsid and domain_id string

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在 2022/10/21 10:31, Jingbo Xu 写道:

When erofs instance is remounted with fsid or domain_id mount option
specified, the original fsid and domain_id string pointer in sbi->opt
is directly overridden with the fsid and domain_id string in the new
fs_context, without freeing the original fsid and domain_id string.
What's worse, when the new fsid and domain_id string is transferred to
sbi, they are not reset to NULL in fs_context, and thus they are freed
when remount finishes, while sbi is still referring to these strings.

Reconfiguration for fsid and domain_id seems unusual. Thus clarify this
restriction explicitly and dump a warning when users are attempting to
do this.

Besides, to fix the use-after-free issue, move fsid and domain_id from
erofs_mount_opts to outside.

Fixes: c6be2bd0a5dd ("erofs: register fscache volume")
Fixes: 8b7adf1dff3d ("erofs: introduce fscache-based domain")
Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>

Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>

---
  fs/erofs/fscache.c  | 14 +++++++-------
  fs/erofs/internal.h |  6 ++++--
  fs/erofs/super.c    | 39 ++++++++++++++++++++++-----------------
  fs/erofs/sysfs.c    |  8 ++++----
  4 files changed, 37 insertions(+), 30 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index fe05bc51f9f2..03de503a1b85 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -403,13 +403,13 @@ static void erofs_fscache_domain_put(struct erofs_domain *domain)
  static int erofs_fscache_register_volume(struct super_block *sb)
  {
  	struct erofs_sb_info *sbi = EROFS_SB(sb);
-	char *domain_id = sbi->opt.domain_id;
+	char *domain_id = sbi->domain_id;
  	struct fscache_volume *volume;
  	char *name;
  	int ret = 0;
name = kasprintf(GFP_KERNEL, "erofs,%s", 
-			 domain_id ? domain_id : sbi->opt.fsid);
+			 domain_id ? domain_id : sbi->fsid);
  	if (!name)
  		return -ENOMEM;
@@ -435,7 +435,7 @@ static int erofs_fscache_init_domain(struct super_block *sb) 
  	if (!domain)
  		return -ENOMEM;
- domain->domain_id = kstrdup(sbi->opt.domain_id, GFP_KERNEL); 
+	domain->domain_id = kstrdup(sbi->domain_id, GFP_KERNEL);
  	if (!domain->domain_id) {
  		kfree(domain);
  		return -ENOMEM;
@@ -472,7 +472,7 @@ static int erofs_fscache_register_domain(struct super_block *sb)
mutex_lock(&erofs_domain_list_lock); 
  	list_for_each_entry(domain, &erofs_domain_list, list) {
-		if (!strcmp(domain->domain_id, sbi->opt.domain_id)) {
+		if (!strcmp(domain->domain_id, sbi->domain_id)) {
  			sbi->domain = domain;
  			sbi->volume = domain->volume;
  			refcount_inc(&domain->ref);
@@ -609,7 +609,7 @@ struct erofs_fscache *erofs_domain_register_cookie(struct super_block *sb,
  struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
  						    char *name, bool need_inode)
  {
-	if (EROFS_SB(sb)->opt.domain_id)
+	if (EROFS_SB(sb)->domain_id)
  		return erofs_domain_register_cookie(sb, name, need_inode);
  	return erofs_fscache_acquire_cookie(sb, name, need_inode);
  }
@@ -641,7 +641,7 @@ int erofs_fscache_register_fs(struct super_block *sb)
  	struct erofs_sb_info *sbi = EROFS_SB(sb);
  	struct erofs_fscache *fscache;
- if (sbi->opt.domain_id) 
+	if (sbi->domain_id)
  		ret = erofs_fscache_register_domain(sb);
  	else
  		ret = erofs_fscache_register_volume(sb);
@@ -649,7 +649,7 @@ int erofs_fscache_register_fs(struct super_block *sb)
  		return ret;
/* acquired domain/volume will be relinquished in kill_sb() on error */ 
-	fscache = erofs_fscache_register_cookie(sb, sbi->opt.fsid, true);
+	fscache = erofs_fscache_register_cookie(sb, sbi->fsid, true);
  	if (IS_ERR(fscache))
  		return PTR_ERR(fscache);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h 
index 1701df48c446..05dc68627722 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -75,8 +75,6 @@ struct erofs_mount_opts {
  	unsigned int max_sync_decompress_pages;
  #endif
  	unsigned int mount_opt;
-	char *fsid;
-	char *domain_id;
  };
struct erofs_dev_context { 
@@ -89,6 +87,8 @@ struct erofs_dev_context {
  struct erofs_fs_context {
  	struct erofs_mount_opts opt;
  	struct erofs_dev_context *devs;
+	char *fsid;
+	char *domain_id;
  };
/* all filesystem-wide lz4 configurations */ 
@@ -170,6 +170,8 @@ struct erofs_sb_info {
  	struct fscache_volume *volume;
  	struct erofs_fscache *s_fscache;
  	struct erofs_domain *domain;
+	char *fsid;
+	char *domain_id;
  };
#define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info) 
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 2cf96ce1c32e..1c7dcca702b3 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -579,9 +579,9 @@ static int erofs_fc_parse_param(struct fs_context *fc,
  		break;
  	case Opt_fsid:
  #ifdef CONFIG_EROFS_FS_ONDEMAND
-		kfree(ctx->opt.fsid);
-		ctx->opt.fsid = kstrdup(param->string, GFP_KERNEL);
-		if (!ctx->opt.fsid)
+		kfree(ctx->fsid);
+		ctx->fsid = kstrdup(param->string, GFP_KERNEL);
+		if (!ctx->fsid)
  			return -ENOMEM;
  #else
  		errorfc(fc, "fsid option not supported");
@@ -589,9 +589,9 @@ static int erofs_fc_parse_param(struct fs_context *fc,
  		break;
  	case Opt_domain_id:
  #ifdef CONFIG_EROFS_FS_ONDEMAND
-		kfree(ctx->opt.domain_id);
-		ctx->opt.domain_id = kstrdup(param->string, GFP_KERNEL);
-		if (!ctx->opt.domain_id)
+		kfree(ctx->domain_id);
+		ctx->domain_id = kstrdup(param->string, GFP_KERNEL);
+		if (!ctx->domain_id)
  			return -ENOMEM;
  #else
  		errorfc(fc, "domain_id option not supported");
@@ -728,10 +728,12 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
sb->s_fs_info = sbi; 
  	sbi->opt = ctx->opt;
-	ctx->opt.fsid = NULL;
-	ctx->opt.domain_id = NULL;
  	sbi->devs = ctx->devs;
  	ctx->devs = NULL;
+	sbi->fsid = ctx->fsid;
+	ctx->fsid = NULL;
+	sbi->domain_id = ctx->domain_id;
+	ctx->domain_id = NULL;
if (erofs_is_fscache_mode(sb)) { 
  		sb->s_blocksize = EROFS_BLKSIZ;
@@ -820,7 +822,7 @@ static int erofs_fc_get_tree(struct fs_context *fc)
  {
  	struct erofs_fs_context *ctx = fc->fs_private;
- if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->opt.fsid) 
+	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->fsid)
  		return get_tree_nodev(fc, erofs_fc_fill_super);
return get_tree_bdev(fc, erofs_fc_fill_super); 
@@ -834,6 +836,9 @@ static int erofs_fc_reconfigure(struct fs_context *fc)
DBG_BUGON(!sb_rdonly(sb)); + if (ctx->fsid || ctx->domain_id) 
+		erofs_info(sb, "ignoring reconfiguration for fsid|domain_id.");
+
  	if (test_opt(&ctx->opt, POSIX_ACL))
  		fc->sb_flags |= SB_POSIXACL;
  	else
@@ -873,8 +878,8 @@ static void erofs_fc_free(struct fs_context *fc)
  	struct erofs_fs_context *ctx = fc->fs_private;
erofs_free_dev_context(ctx->devs); 
-	kfree(ctx->opt.fsid);
-	kfree(ctx->opt.domain_id);
+	kfree(ctx->fsid);
+	kfree(ctx->domain_id);
  	kfree(ctx);
  }
@@ -944,8 +949,8 @@ static void erofs_kill_sb(struct super_block *sb) 
  	erofs_free_dev_context(sbi->devs);
  	fs_put_dax(sbi->dax_dev, NULL);
  	erofs_fscache_unregister_fs(sb);
-	kfree(sbi->opt.fsid);
-	kfree(sbi->opt.domain_id);
+	kfree(sbi->fsid);
+	kfree(sbi->domain_id);
  	kfree(sbi);
  	sb->s_fs_info = NULL;
  }
@@ -1098,10 +1103,10 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
  	if (test_opt(opt, DAX_NEVER))
  		seq_puts(seq, ",dax=never");
  #ifdef CONFIG_EROFS_FS_ONDEMAND
-	if (opt->fsid)
-		seq_printf(seq, ",fsid=%s", opt->fsid);
-	if (opt->domain_id)
-		seq_printf(seq, ",domain_id=%s", opt->domain_id);
+	if (sbi->fsid)
+		seq_printf(seq, ",fsid=%s", sbi->fsid);
+	if (sbi->domain_id)
+		seq_printf(seq, ",domain_id=%s", sbi->domain_id);
  #endif
  	return 0;
  }
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index 783bb7b21b51..fd476961f742 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -210,14 +210,14 @@ int erofs_register_sysfs(struct super_block *sb)
  	int err;
if (erofs_is_fscache_mode(sb)) { 
-		if (sbi->opt.domain_id) {
-			str = kasprintf(GFP_KERNEL, "%s,%s", sbi->opt.domain_id,
-					sbi->opt.fsid);
+		if (sbi->domain_id) {
+			str = kasprintf(GFP_KERNEL, "%s,%s", sbi->domain_id,
+					sbi->fsid);
  			if (!str)
  				return -ENOMEM;
  			name = str;
  		} else {
-			name = sbi->opt.fsid;
+			name = sbi->fsid;
  		}
  	} else {
  		name = sb->s_id;
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