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SubjectRe: [PATCH] Smack: check for SMACK xattr max size in smack_inode_setxattr
Casey Schaufler wrote:
> Etienne Basset wrote:
>> the following patch move the check for SMACK xattr size >= SMK_LABELLEN
>> from smack_inode_post_setxattr (which cannot return an error to the user)
>> to smack_inode_setxattr (which can return an error).
>>
>> without patch a SMACK setxattr with size >= SMK_LABELLEN returns success although it doesn't
>>
>
> How about an early call to smk_import() to determine if the
> label if legitimate, rather than checking the length? That
> could save grief for other "invalid label" issues.

Hi,

both are needed. And we'll need one call in setxattr to check the validity and one in
postsetxattr/ inode_setsecurity (to set the security blob)
(which make me think we should split smk_import in 2, smk_check/smk_import_nocheck or whatever)

The harder issue is that smk_import can change the value/size of the xattr
and smk_import can fail for 2 reasons : ENOMEM or EINVAL (not sure this is an issue though)
(we should really split)

root@etienne-desktop:/tmp# attr -S -s SMACK64 -V '123////' toto
Attribute "SMACK64" set to a 7 byte value for toto:
123////
root@etienne-desktop:/tmp# attr -S -g SMACK64 toto
Attribute "SMACK64" had a 4 byte value for toto:
123

maybe it would be nicer to fail than change the label under the foot of the-user-who-hasnt-read-the-doc?

Etienne
>
>> Signed-off-by: Etienne Basset <etienne.basset@numericable.fr>
>> ---
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index 9215149..da6954d 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -610,7 +610,8 @@ static int smack_inode_setxattr(struct dentry *dentry, const char *name,
>> if (!capable(CAP_MAC_ADMIN))
>> rc = -EPERM;
>> /* a label cannot be void and cannot begin with '-' */
>> - if (size == 0 || (size > 0 && ((char *)value)[0] == '-'))
>> + if (size == 0 || size >= SMK_LABELLEN ||
>> + (size > 0 && ((char *)value)[0] == '-'))
>> rc = -EINVAL;
>> } else
>> rc = cap_inode_setxattr(dentry, name, value, size, flags);
>> @@ -644,9 +645,6 @@ static void smack_inode_post_setxattr(struct dentry *dentry, const char *name,
>> if (strcmp(name, XATTR_NAME_SMACK))
>> return;
>>
>> - if (size >= SMK_LABELLEN)
>> - return;
>> -
>> isp = dentry->d_inode->i_security;
>>
>> /*
>>
>> --
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>>
>>
>
>



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