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SubjectRe: [PATCH 07/18] fs_context: fix double free of legacy_fs_context data
Date
Eric Biggers <ebiggers3@gmail.com> wrote:

> sys_fsmount() calls fc->ops->free() to free the data, zeroes
> ->fs_private, then proceeds to reuse the context. But legacy_fs_context
> doesn't use ->fs_private, so we need to handle zeroing it too; otherwise
> there's a double free of legacy_fs_context::{legacy_data,secdata}.

I think the attached is better. I stopped embedding the fs_context in the
xxx_fs_context to make certain things simpler, but I missed the legacy
wrapper.

David
---
diff --git a/fs/fs_context.c b/fs/fs_context.c
index f91facc769f7..ab93a0b73dc6 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -34,7 +34,6 @@ enum legacy_fs_param {
};

struct legacy_fs_context {
- struct fs_context fc;
char *legacy_data; /* Data page for legacy filesystems */
char *secdata;
size_t data_size;
@@ -239,12 +238,21 @@ struct fs_context *vfs_new_fs_context(struct file_system_type *fs_type,
enum fs_context_purpose purpose)
{
struct fs_context *fc;
- int ret;
+ int ret = -ENOMEM;

- fc = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
+ fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
if (!fc)
return ERR_PTR(-ENOMEM);

+ if (!fs_type->init_fs_context) {
+ fc->fs_private = kzalloc(sizeof(struct legacy_fs_context),
+ GFP_KERNEL);
+ if (!fc->fs_private)
+ goto err_fc;
+
+ fc->ops = &legacy_fs_context_ops;
+ }
+
fc->purpose = purpose;
fc->sb_flags = sb_flags;
fc->fs_type = get_filesystem(fs_type);
@@ -277,8 +285,6 @@ struct fs_context *vfs_new_fs_context(struct file_system_type *fs_type,
ret = fc->fs_type->init_fs_context(fc, reference);
if (ret < 0)
goto err_fc;
- } else {
- fc->ops = &legacy_fs_context_ops;
}

/* Do the security check last because ->init_fs_context may change the
@@ -395,7 +401,7 @@ EXPORT_SYMBOL(put_fs_context);
*/
static void legacy_fs_context_free(struct fs_context *fc)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx = fc->fs_private;

free_secdata(ctx->secdata);
switch (ctx->param_type) {
@@ -408,6 +414,8 @@ static void legacy_fs_context_free(struct fs_context *fc)
kfree(ctx->legacy_data);
break;
}
+
+ kfree(ctx);
}

/*
@@ -415,20 +423,28 @@ static void legacy_fs_context_free(struct fs_context *fc)
*/
static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
- struct legacy_fs_context *src_ctx = container_of(src_fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx;
+ struct legacy_fs_context *src_ctx = src_fc->fs_private;
+
+ ctx = kmemdup(src_ctx, sizeof(*src_ctx), GFP_KERNEL);
+ if (!ctx)
+ return -ENOMEM;

switch (ctx->param_type) {
case LEGACY_FS_MONOLITHIC_PARAMS:
case LEGACY_FS_INDIVIDUAL_PARAMS:
ctx->legacy_data = kmemdup(src_ctx->legacy_data,
src_ctx->data_size, GFP_KERNEL);
- if (!ctx->legacy_data)
+ if (!ctx->legacy_data) {
+ kfree(ctx);
return -ENOMEM;
+ }
/* Fall through */
default:
break;
}
+
+ fc->fs_private = ctx;
return 0;
}

@@ -438,7 +454,7 @@ static int legacy_fs_context_dup(struct fs_context *fc, struct fs_context *src_f
*/
static int legacy_parse_option(struct fs_context *fc, char *opt, size_t len)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx = fc->fs_private;
unsigned int size = ctx->data_size;

if (ctx->param_type != LEGACY_FS_UNSET_PARAMS &&
@@ -471,7 +487,7 @@ static int legacy_parse_option(struct fs_context *fc, char *opt, size_t len)
*/
static int legacy_parse_monolithic(struct fs_context *fc, void *data, size_t data_size)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx = fc->fs_private;

if (ctx->param_type != LEGACY_FS_UNSET_PARAMS) {
pr_warn("VFS: Can't mix monolithic and individual options\n");
@@ -507,7 +523,7 @@ static int legacy_parse_monolithic(struct fs_context *fc, void *data, size_t dat
*/
static int legacy_validate(struct fs_context *fc)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx = fc->fs_private;

switch (ctx->param_type) {
case LEGACY_FS_UNSET_PARAMS:
@@ -520,7 +536,7 @@ static int legacy_validate(struct fs_context *fc)
break;
}

- if (ctx->fc.fs_type->fs_flags & FS_BINARY_MOUNTDATA)
+ if (fc->fs_type->fs_flags & FS_BINARY_MOUNTDATA)
return 0;

ctx->secdata = alloc_secdata();
@@ -557,13 +573,13 @@ static int legacy_set_subtype(struct fs_context *fc)
*/
static int legacy_get_tree(struct fs_context *fc)
{
- struct legacy_fs_context *ctx = container_of(fc, struct legacy_fs_context, fc);
+ struct legacy_fs_context *ctx = fc->fs_private;
struct super_block *sb;
struct dentry *root;
int ret;

- root = ctx->fc.fs_type->mount(ctx->fc.fs_type, ctx->fc.sb_flags,
- ctx->fc.source, ctx->legacy_data,
+ root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
+ fc->source, ctx->legacy_data,
ctx->data_size);
if (IS_ERR(root))
return PTR_ERR(root);
@@ -571,14 +587,14 @@ static int legacy_get_tree(struct fs_context *fc)
sb = root->d_sb;
BUG_ON(!sb);

- if ((ctx->fc.fs_type->fs_flags & FS_HAS_SUBTYPE) &&
+ if ((fc->fs_type->fs_flags & FS_HAS_SUBTYPE) &&
!fc->subtype) {
ret = legacy_set_subtype(fc);
if (ret < 0)
goto err_sb;
}

- ctx->fc.root = root;
+ fc->root = root;
return 0;

err_sb:
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