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SubjectRe: [PATCH v11 2/4] smack: Set the SMACK64TRANSMUTE xattr in smack_inode_init_security()
From
On 6/9/2023 9:35 PM, Mimi Zohar wrote:
> Hi Roberto,
>
> On Sat, 2023-06-03 at 21:15 +0200, Roberto Sassu wrote:
>> From: Roberto Sassu <roberto.sassu@huawei.com>
>>
>> With the newly added ability of LSMs to supply multiple xattrs, set
>> SMACK64TRASMUTE in smack_inode_init_security(), instead of d_instantiate().
>> Do it by incrementing SMACK_INODE_INIT_XATTRS to 2 and by calling
>> lsm_get_xattr_slot() a second time, if the transmuting conditions are met.
>>
>> The LSM infrastructure passes all xattrs provided by LSMs to the
>> filesystems through the initxattrs() callback, so that filesystems can
>> store xattrs in the disk.
>>
>> After the change, the SMK_INODE_TRANSMUTE inode flag is always set by
>> d_instantiate() after fetching SMACK64TRANSMUTE from the disk. Before it
>> was done by smack_inode_post_setxattr() as result of the __vfs_setxattr()
>> call.
>>
>> Removing __vfs_setxattr() also prevents invalidating the EVM HMAC, by
>> adding a new xattr without checking and updating the existing HMAC.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
>
> Just a few comments/nits inline.
>
>> ---
>> security/smack/smack.h | 2 +-
>> security/smack/smack_lsm.c | 43 +++++++++++++++++++++++---------------
>> 2 files changed, 27 insertions(+), 18 deletions(-)
>>
>> diff --git a/security/smack/smack.h b/security/smack/smack.h
>> index aa15ff56ed6..041688e5a77 100644
>> --- a/security/smack/smack.h
>> +++ b/security/smack/smack.h
>> @@ -128,7 +128,7 @@ struct task_smack {
>>
>> #define SMK_INODE_INSTANT 0x01 /* inode is instantiated */
>> #define SMK_INODE_TRANSMUTE 0x02 /* directory is transmuting */
>> -#define SMK_INODE_CHANGED 0x04 /* smack was transmuted */
>> +#define SMK_INODE_CHANGED 0x04 /* smack was transmuted (unused) */
>> #define SMK_INODE_IMPURE 0x08 /* involved in an impure transaction */
>>
>> /*
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index a1c30275692..b67d901ee74 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -52,7 +52,14 @@
>> #define SMK_RECEIVING 1
>> #define SMK_SENDING 2
>>
>> -#define SMACK_INODE_INIT_XATTRS 1
>> +/*
>> + * Smack uses multiple xattrs.
>> + * SMACK64 - for access control,
>> + * SMACK64TRANSMUTE - label initialization,
>> + * Not saved on files - SMACK64IPIN and SMACK64IPOUT,
>> + * Must be set explicitly - SMACK64EXEC and SMACK64MMAP
>> + */
>> +#define SMACK_INODE_INIT_XATTRS 2
>>
>> #ifdef SMACK_IPV6_PORT_LABELING
>> static DEFINE_MUTEX(smack_ipv6_lock);
>> @@ -935,7 +942,6 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
>> struct xattr *xattrs, int *xattr_count)
>> {
>> struct task_smack *tsp = smack_cred(current_cred());
>> - struct inode_smack *issp = smack_inode(inode);
>> struct smack_known *skp = smk_of_task(tsp);
>> struct smack_known *isp = smk_of_inode(inode);
>> struct smack_known *dsp = smk_of_inode(dir);
>> @@ -963,6 +969,8 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
>> if ((tsp->smk_task == tsp->smk_transmuted) ||
>> (may > 0 && ((may & MAY_TRANSMUTE) != 0) &&
>> smk_inode_transmutable(dir))) {
>> + struct xattr *xattr_transmute;
>> +
>
> Variables should be defined at the beginning of the function.

Casey asked to declare the variable in this block.

> Is there a reason for beginning the function with "if (xattr) {"
> instead "if (!xattr) return 0;". This causes unnecessary indenting.

I revisited this part and made few fixes:

https://lore.kernel.org/linux-security-module/20230607123612.2791303-1-roberto.sassu@huaweicloud.com/

Patch 3 should address your concern.

>> /*
>> * The caller of smack_dentry_create_files_as()
>> * should have overridden the current cred, so the
>> @@ -971,7 +979,16 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
>> */
>> if (tsp->smk_task != tsp->smk_transmuted)
>> isp = dsp;
>> - issp->smk_flags |= SMK_INODE_CHANGED;
>> + xattr_transmute = lsm_get_xattr_slot(xattrs, xattr_count);
>> + if (xattr_transmute) {
>> + xattr_transmute->value = kmemdup(TRANS_TRUE,
>> + TRANS_TRUE_SIZE, GFP_NOFS);
>
> script/checkpatch --strict complains here.

Thanks, I didn't know about it.

It seems that they are more stylistic things. Probably, not worth to
respin the patch set just for those (unless you prefer I do it).

Thanks

Roberto

>> + if (xattr_transmute->value == NULL)
>> + return -ENOMEM;
>> +
>> + xattr_transmute->value_len = TRANS_TRUE_SIZE;
>> + xattr_transmute->name = XATTR_SMACK_TRANSMUTE;
>> + }
>> }
>>
>> xattr->value = kstrdup(isp->smk_known, GFP_NOFS);
>> @@ -3518,20 +3535,12 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>> * If there is a transmute attribute on the
>> * directory mark the inode.
>> */
>> - if (isp->smk_flags & SMK_INODE_CHANGED) {
>> - isp->smk_flags &= ~SMK_INODE_CHANGED;
>> - rc = __vfs_setxattr(&nop_mnt_idmap, dp, inode,
>> - XATTR_NAME_SMACKTRANSMUTE,
>> - TRANS_TRUE, TRANS_TRUE_SIZE,
>> - 0);
>> - } else {
>> - rc = __vfs_getxattr(dp, inode,
>> - XATTR_NAME_SMACKTRANSMUTE, trattr,
>> - TRANS_TRUE_SIZE);
>> - if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
>> - TRANS_TRUE_SIZE) != 0)
>> - rc = -EINVAL;
>> - }
>> + rc = __vfs_getxattr(dp, inode,
>> + XATTR_NAME_SMACKTRANSMUTE, trattr,
>> + TRANS_TRUE_SIZE);
>> + if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
>> + TRANS_TRUE_SIZE) != 0)
>> + rc = -EINVAL;
>> if (rc >= 0)
>> transflag = SMK_INODE_TRANSMUTE;
>> }
>
>

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