[Devel] [PATCH] ext4: release leaked posix acl in ext4_xattr_set_acl

[Stanislav Kinsburskiy]

07.02.2018 14:51, Dmitry Monakhov пишет:
> Stanislav Kinsburskiy <skinsbursky at virtuozzo.com> writes:
> 
>> Posix acl is used to convert of an extended attribute, provided by user to
>> ext4 attributes. In particular to I-mode in case of ACL_TYPE_ACCESS request.
>> IOW, this object is allocated, used for convertion, not stored anywhere and
>> must be freed.
>> However posix_acl_update_mode() can zerofy the pointer to support
>> ext4_set_acl() logic, but then the object is leaked.
>> So, fix it by releasing new temporary pointer with the same value instead of
>> acl pointer.
> So you are telling me that:
> ext4_xattr_set_acl
> L1 acl = posix_acl_from_xattr 
> L2 -> ext4_set_acl(handle, inode, type, acl)
> L3    ->posix_acl_update_mode(inode, &inode->i_mode, &acl)
>       *acl = NULL;
>       You are saying that instruction above can affect value at L1?
>       HOW? acl passed to ext4_set_acl() by value, so
>       posix_acl_update_mode() can affect value only in L2 and L3 but not L1. 
> 
> Stas, have you drunk a lousy beer today?

OMG, Dmitry... Looks like storage work clouded your mind and you are looking to some other sources.
There is no "L3" in the bug.
Because posix_acl_update_mode() in called from ext4_xattr_set_acl() (i.e on "L2").
Thus pointer is set to NULL on "L2" and released on "L1".
IOW, pointer is leaked.


>>
>> https://jira.sw.ru/browse/PSBM-81384
>>
>> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
>> ---
>>  fs/ext4/acl.c |    8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
>> index 917e819..2640d7b 100644
>> --- a/fs/ext4/acl.c
>> +++ b/fs/ext4/acl.c
>> @@ -403,7 +403,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>>  {
>>  	struct inode *inode = dentry->d_inode;
>>  	handle_t *handle;
>> -	struct posix_acl *acl;
>> +	struct posix_acl *acl, *tmp;
>>  	int error, retries = 0;
>>  	int update_mode = 0;
>>  	umode_t mode = inode->i_mode;
>> @@ -416,7 +416,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>>  		return -EPERM;
>>  
>>  	if (value) {
>> -		acl = posix_acl_from_xattr(&init_user_ns, value, size);
>> +		acl = tmp = posix_acl_from_xattr(&init_user_ns, value, size);
>>  		if (IS_ERR(acl))
>>  			return PTR_ERR(acl);
>>  		else if (acl) {
>> @@ -425,7 +425,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>>  				goto release_and_out;
>>  		}
>>  	} else
>> -		acl = NULL;
>> +		acl = tmp = NULL;
>>  
>>  retry:
>>  	handle = ext4_journal_start(inode, EXT4_HT_XATTR,
>> @@ -452,7 +452,7 @@ ext4_xattr_set_acl(struct dentry *dentry, const char *name, const void *value,
>>  		goto retry;
>>  
>>  release_and_out:
>> -	posix_acl_release(acl);
>> +	posix_acl_release(tmp);
>>  	return error;
>>  }
>>