hulk inclusion category: feature feature: digest-lists
---------------------------
By default, EVM maintains the same behavior as before hooks were moved outside the LSM infrastructure. When EVM returns -EPERM, callers stop their execution and return the error to user space.
This patch introduces a new mode, called ignore, that changes the return value of the pre hooks from -EPERM to -EAGAIN. It also modifies the callers of pre and post hooks to continue the execution if -EAGAIN is returned. The error is then handled by the post hooks.
The only error that is not ignored is when user space is trying to modify immutable metadata. Once that signature has been validated with the current values of metadata, there is no valid reason to change them.
From user space perspective, operations on corrupted metadata are successfully performed but post hooks didn't update the HMAC. At the next IMA verification, when evm_verifyxattr() is called, corruption will be detected and access will be denied.
Signed-off-by: Roberto Sassu roberto.sassu@huawei.com --- fs/attr.c | 2 +- fs/xattr.c | 4 ++-- security/integrity/evm/evm_main.c | 24 ++++++++++++++++++------ 3 files changed, 21 insertions(+), 9 deletions(-)
diff --git a/fs/attr.c b/fs/attr.c index 9a632198c07c..a96871b6ba7d 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -327,7 +327,7 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de if (error) return error; evm_error = evm_inode_setattr(dentry, attr); - if (evm_error) + if (evm_error && evm_error != -EAGAIN) return evm_error; error = try_break_deleg(inode, delegated_inode); if (error) diff --git a/fs/xattr.c b/fs/xattr.c index 64ebf7b7fe89..adb11cb82be5 100644 --- a/fs/xattr.c +++ b/fs/xattr.c @@ -240,7 +240,7 @@ __vfs_setxattr_locked(struct dentry *dentry, const char *name, goto out;
evm_error = evm_inode_setxattr(dentry, name, value, size); - if (evm_error) { + if (evm_error && evm_error != -EAGAIN) { error = evm_error; goto out; } @@ -454,7 +454,7 @@ __vfs_removexattr_locked(struct dentry *dentry, const char *name, goto out;
evm_error = evm_inode_removexattr(dentry, name); - if (evm_error) { + if (evm_error && evm_error != -EAGAIN) { error = evm_error; goto out; } diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index f0b515334171..181f4758e3bd 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -61,7 +61,7 @@ static struct xattr_list evm_config_default_xattrnames[] = {
LIST_HEAD(evm_config_xattrnames);
-static int evm_fixmode; +static int evm_fixmode, evm_ignoremode __ro_after_init; static int __init evm_set_param(char *str) { if (strncmp(str, "fix", 3) == 0) @@ -70,6 +70,8 @@ static int __init evm_set_param(char *str) evm_initialized |= EVM_INIT_X509; else if (strncmp(str, "allow_metadata_writes", 21) == 0) evm_initialized |= EVM_ALLOW_METADATA_WRITES; + else if (strncmp(str, "ignore", 6) == 0) + evm_ignoremode = 1; return 0; } __setup("evm=", evm_set_param); @@ -450,6 +452,7 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, const void *xattr_value, size_t xattr_value_len) { enum integrity_status evm_status; + int rc = -EPERM;
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { if (!capable(CAP_SYS_ADMIN)) @@ -494,12 +497,17 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, !evm_xattr_change(dentry, xattr_name, xattr_value, xattr_value_len)) return 0;
- if (evm_status != INTEGRITY_PASS) + if (evm_status != INTEGRITY_PASS) { + if (evm_ignoremode && evm_status != INTEGRITY_PASS_IMMUTABLE) + rc = -EAGAIN; + integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", integrity_status_msg[evm_status], - -EPERM, 0); - return evm_status == INTEGRITY_PASS ? 0 : -EPERM; + rc, 0); + } + + return evm_status == INTEGRITY_PASS ? 0 : rc; }
/** @@ -659,6 +667,7 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) { unsigned int ia_valid = attr->ia_valid; enum integrity_status evm_status; + int rc = -EPERM;
/* Policy permits modification of the protected attrs even though * there's no HMAC key loaded @@ -681,10 +690,13 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) !evm_attr_change(dentry, attr)) return 0;
+ if (evm_ignoremode && evm_status != INTEGRITY_PASS_IMMUTABLE) + rc = -EAGAIN; + integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", - integrity_status_msg[evm_status], -EPERM, 0); - return -EPERM; + integrity_status_msg[evm_status], rc, 0); + return rc; }
/**