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SubjectRe: [PATCH] configfs: Fix use-after-free issue in __configfs_open_file
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Hi Joel, Christoph, Al

Does any one have time to review this patch, ten days past...

Thanks,

On 2021/3/5 11:29, Chao Yu wrote:
> +Cc fsdevel
>
> Ping,
>
> Any comments one this patch?
>
> On 2021/3/1 14:10, Chao Yu wrote:
>> From: Daiyue Zhang <zhangdaiyue1@huawei.com>
>>
>> Commit b0841eefd969 ("configfs: provide exclusion between IO and removals")
>> uses ->frag_dead to mark the fragment state, thus no bothering with extra
>> refcount on config_item when opening a file. The configfs_get_config_item
>> was removed in __configfs_open_file, but not with config_item_put. So the
>> refcount on config_item will lost its balance, causing use-after-free
>> issues in some occasions like this:
>>
>> Test:
>> 1. Mount configfs on /config with read-only items:
>> drwxrwx--- 289 root root 0 2021-04-01 11:55 /config
>> drwxr-xr-x 2 root root 0 2021-04-01 11:54 /config/a
>> --w--w--w- 1 root root 4096 2021-04-01 11:53 /config/a/1.txt
>> ......
>>
>> 2. Then run:
>> for file in /config
>> do
>> echo $file
>> grep -R 'key' $file
>> done
>>
>> 3. __configfs_open_file will be called in parallel, the first one
>> got called will do:
>> if (file->f_mode & FMODE_READ) {
>> if (!(inode->i_mode & S_IRUGO))
>> goto out_put_module;
>> config_item_put(buffer->item);
>> kref_put()
>> package_details_release()
>> kfree()
>>
>> the other one will run into use-after-free issues like this:
>> BUG: KASAN: use-after-free in __configfs_open_file+0x1bc/0x3b0
>> Read of size 8 at addr fffffff155f02480 by task grep/13096
>> CPU: 0 PID: 13096 Comm: grep VIP: 00 Tainted: G W 4.14.116-kasan #1
>> TGID: 13096 Comm: grep
>> Call trace:
>> dump_stack+0x118/0x160
>> kasan_report+0x22c/0x294
>> __asan_load8+0x80/0x88
>> __configfs_open_file+0x1bc/0x3b0
>> configfs_open_file+0x28/0x34
>> do_dentry_open+0x2cc/0x5c0
>> vfs_open+0x80/0xe0
>> path_openat+0xd8c/0x2988
>> do_filp_open+0x1c4/0x2fc
>> do_sys_open+0x23c/0x404
>> SyS_openat+0x38/0x48
>>
>> Allocated by task 2138:
>> kasan_kmalloc+0xe0/0x1ac
>> kmem_cache_alloc_trace+0x334/0x394
>> packages_make_item+0x4c/0x180
>> configfs_mkdir+0x358/0x740
>> vfs_mkdir2+0x1bc/0x2e8
>> SyS_mkdirat+0x154/0x23c
>> el0_svc_naked+0x34/0x38
>>
>> Freed by task 13096:
>> kasan_slab_free+0xb8/0x194
>> kfree+0x13c/0x910
>> package_details_release+0x524/0x56c
>> kref_put+0xc4/0x104
>> config_item_put+0x24/0x34
>> __configfs_open_file+0x35c/0x3b0
>> configfs_open_file+0x28/0x34
>> do_dentry_open+0x2cc/0x5c0
>> vfs_open+0x80/0xe0
>> path_openat+0xd8c/0x2988
>> do_filp_open+0x1c4/0x2fc
>> do_sys_open+0x23c/0x404
>> SyS_openat+0x38/0x48
>> el0_svc_naked+0x34/0x38
>>
>> To fix this issue, remove the config_item_put in
>> __configfs_open_file to balance the refcount of config_item.
>>
>> Fixes: b0841eefd969 ("configfs: provide exclusion between IO and removals")
>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>> Cc: Joel Becker <jlbec@evilplan.org>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Daiyue Zhang <zhangdaiyue1@huawei.com>
>> Signed-off-by: Yi Chen <chenyi77@huawei.com>
>> Signed-off-by: Ge Qiu <qiuge@huawei.com>
>> Reviewed-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> fs/configfs/file.c | 6 ++----
>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/configfs/file.c b/fs/configfs/file.c
>> index 1f0270229d7b..da8351d1e455 100644
>> --- a/fs/configfs/file.c
>> +++ b/fs/configfs/file.c
>> @@ -378,7 +378,7 @@ static int __configfs_open_file(struct inode *inode, struct file *file, int type
>>
>> attr = to_attr(dentry);
>> if (!attr)
>> - goto out_put_item;
>> + goto out_free_buffer;
>>
>> if (type & CONFIGFS_ITEM_BIN_ATTR) {
>> buffer->bin_attr = to_bin_attr(dentry);
>> @@ -391,7 +391,7 @@ static int __configfs_open_file(struct inode *inode, struct file *file, int type
>> /* Grab the module reference for this attribute if we have one */
>> error = -ENODEV;
>> if (!try_module_get(buffer->owner))
>> - goto out_put_item;
>> + goto out_free_buffer;
>>
>> error = -EACCES;
>> if (!buffer->item->ci_type)
>> @@ -435,8 +435,6 @@ static int __configfs_open_file(struct inode *inode, struct file *file, int type
>>
>> out_put_module:
>> module_put(buffer->owner);
>> -out_put_item:
>> - config_item_put(buffer->item);
>> out_free_buffer:
>> up_read(&frag->frag_sem);
>> kfree(buffer);
>>
> .
>

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