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    Subject[PATCH v6 20/20] evm: add evm_inode_setattr to prevent updating an invalid security.evm
    Date
    Permit changing of security.evm only when valid, unless in fixmode.

    Reported-by: Roberto Sassu <roberto.sassu@polito.it>
    Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
    ---
    include/linux/evm.h | 6 ++++++
    security/integrity/evm/evm_main.c | 15 +++++++++++++++
    security/security.c | 7 ++++++-
    3 files changed, 27 insertions(+), 1 deletions(-)

    diff --git a/include/linux/evm.h b/include/linux/evm.h
    index 8db7b74..afc0669 100644
    --- a/include/linux/evm.h
    +++ b/include/linux/evm.h
    @@ -19,6 +19,7 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
    void *xattr_value,
    size_t xattr_value_len,
    struct integrity_iint_cache *iint);
    +extern int evm_inode_setattr(struct dentry *dentry, struct iattr *attr);
    extern void evm_inode_post_setattr(struct dentry *dentry, int ia_valid);
    extern int evm_inode_setxattr(struct dentry *dentry, const char *name,
    const void *value, size_t size);
    @@ -44,6 +45,11 @@ static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
    }
    #endif

    +static int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
    +{
    + return 0;
    +}
    +
    static inline void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
    {
    return;
    diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
    index 03524e4..b0ce1e7 100644
    --- a/security/integrity/evm/evm_main.c
    +++ b/security/integrity/evm/evm_main.c
    @@ -278,6 +278,21 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
    }

    /**
    + * evm_inode_setattr - prevent updating an invalid EVM extended attribute
    + * @dentry: pointer to the affected dentry
    + */
    +int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
    +{
    + unsigned int ia_valid = attr->ia_valid;
    + enum integrity_status evm_status;
    +
    + if (ia_valid & ~(ATTR_MODE | ATTR_UID | ATTR_GID))
    + return 0;
    + evm_status = evm_verify_current_integrity(dentry);
    + return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
    +}
    +
    +/**
    * evm_inode_post_setattr - update 'security.evm' after modifying metadata
    * @dentry: pointer to the affected dentry
    * @ia_valid: for the UID and GID status
    diff --git a/security/security.c b/security/security.c
    index e00d2d7..4e9b89f 100644
    --- a/security/security.c
    +++ b/security/security.c
    @@ -532,9 +532,14 @@ int security_inode_exec_permission(struct inode *inode, unsigned int flags)

    int security_inode_setattr(struct dentry *dentry, struct iattr *attr)
    {
    + int ret;
    +
    if (unlikely(IS_PRIVATE(dentry->d_inode)))
    return 0;
    - return security_ops->inode_setattr(dentry, attr);
    + ret = security_ops->inode_setattr(dentry, attr);
    + if (ret)
    + return ret;
    + return evm_inode_setattr(dentry, attr);
    }
    EXPORT_SYMBOL_GPL(security_inode_setattr);

    --
    1.7.3.4


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