On Wed, 2022-10-26 at 16:30 +0200, Nicolas Bouchinet wrote: > From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> > > Fixes a NULL pointer dereference occurring in the > `evm_protected_xattr_common` function of the EVM LSM. The bug is > triggered if a `inode_init_security` hook returns 0 without initializing > the given `struct xattr` fields (which is the case of BPF) and if no > other LSM overrides thoses fields after. This also leads to memory > leaks. > > The `call_int_hook_xattr` macro has been inlined into the > `security_inode_init_security` hook in order to check hooks return > values and skip ones who doesn't init `xattrs`. > > Modify `evm_init_hmac` function to init the EVM hmac using every > entry of the given xattr array. > > The `MAX_LSM_EVM_XATTR` value is now based on the security modules > compiled in, which gives room for SMACK, SELinux, Apparmor, BPF and > IMA/EVM security attributes. > > Changes the default return value of the `inode_init_security` hook > definition to `-EOPNOTSUPP`. > > Changes the hook documentation to match the behavior of the LSMs using > it (only xattr->value is initialised with kmalloc and thus is the only > one that should be kfreed by the caller). > > Cc: roberto.sassu@xxxxxxxxxxxxxxx > Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> > --- > Changes since v3: > https://lore.kernel.org/linux-integrity/Y1fu4jofqLHVDprT@archlinux/ > > * Fixes compilation error reported by the kernel test robot. > --- > include/linux/lsm_hook_defs.h | 2 +- > include/linux/lsm_hooks.h | 4 ++-- > security/integrity/evm/evm.h | 1 + > security/integrity/evm/evm_crypto.c | 9 +++++++-- > security/integrity/evm/evm_main.c | 7 ++++--- > security/security.c | 31 ++++++++++++++++++++++------- > 6 files changed, 39 insertions(+), 15 deletions(-) > > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h > index 806448173033..e5dd0c0f6345 100644 > --- a/include/linux/lsm_hook_defs.h > +++ b/include/linux/lsm_hook_defs.h > @@ -111,7 +111,7 @@ LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask, > unsigned int obj_type) > LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode) > LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode) > -LSM_HOOK(int, 0, inode_init_security, struct inode *inode, > +LSM_HOOK(int, -EOPNOTSUPP, inode_init_security, struct inode *inode, > struct inode *dir, const struct qstr *qstr, const char **name, > void **value, size_t *len) > LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode, > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > index 84a0d7e02176..95aff9383de1 100644 > --- a/include/linux/lsm_hooks.h > +++ b/include/linux/lsm_hooks.h > @@ -229,8 +229,8 @@ > * This hook is called by the fs code as part of the inode creation > * transaction and provides for atomic labeling of the inode, unlike > * the post_create/mkdir/... hooks called by the VFS. The hook function > - * is expected to allocate the name and value via kmalloc, with the caller > - * being responsible for calling kfree after using them. > + * is expected to allocate the value via kmalloc, with the caller > + * being responsible for calling kfree after using it. Please also update the description of @name as well (remove allocated). > * If the security module does not use security attributes or does > * not wish to put a security attribute on this particular inode, > * then it should return -EOPNOTSUPP to skip this processing. > diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h > index f8b8c5004fc7..6d9628ca7c24 100644 > --- a/security/integrity/evm/evm.h > +++ b/security/integrity/evm/evm.h > @@ -61,5 +61,6 @@ int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name, > int evm_init_hmac(struct inode *inode, const struct xattr *xattr, > char *hmac_val); > int evm_init_secfs(void); > +int evm_protected_xattr(const char *req_xattr_name); > > #endif > diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c > index 708de9656bbd..06639f3cfb38 100644 > --- a/security/integrity/evm/evm_crypto.c > +++ b/security/integrity/evm/evm_crypto.c > @@ -385,7 +385,7 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name, > return rc; > } > > -int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, > +int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattrs, > char *hmac_val) > { > struct shash_desc *desc; > @@ -396,7 +396,12 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr, > return PTR_ERR(desc); > } > > - crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len); > + for (int i = 0; lsm_xattrs[i].value != NULL; i++) { > + if (evm_protected_xattr(lsm_xattrs[i].name)) > + crypto_shash_update(desc, > + lsm_xattrs[i].value, > + lsm_xattrs[i].value_len); > + } > hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val); > kfree(desc); > return 0; > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > index 2e6fb6e2ffd2..0420453a80e8 100644 > --- a/security/integrity/evm/evm_main.c > +++ b/security/integrity/evm/evm_main.c > @@ -284,6 +284,8 @@ static int evm_protected_xattr_common(const char *req_xattr_name, > int found = 0; > struct xattr_list *xattr; > > + if (!req_xattr_name) > + return found; Remove, and use the check below. > namelen = strlen(req_xattr_name); > list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) { > if (!all_xattrs && !xattr->enabled) > @@ -305,7 +307,7 @@ static int evm_protected_xattr_common(const char *req_xattr_name, > return found; > } > > -static int evm_protected_xattr(const char *req_xattr_name) > +int evm_protected_xattr(const char *req_xattr_name) > { > return evm_protected_xattr_common(req_xattr_name, false); > } > @@ -841,8 +843,7 @@ int evm_inode_init_security(struct inode *inode, > struct evm_xattr *xattr_data; > int rc; > > - if (!(evm_initialized & EVM_INIT_HMAC) || > - !evm_protected_xattr(lsm_xattr->name)) > + if (!(evm_initialized & EVM_INIT_HMAC)) > return 0; > > xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS); > diff --git a/security/security.c b/security/security.c > index 14d30fec8a00..79524f8734f1 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -30,7 +30,11 @@ > #include <linux/msg.h> > #include <net/flow.h> > > -#define MAX_LSM_EVM_XATTR 2 > +#define MAX_LSM_EVM_XATTR \ > + ((IS_ENABLED(CONFIG_EVM) ? 1 : 0) + \ > + (IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \ > + (IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \ > + (IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0)) > > /* How many LSMs were built into the kernel? */ > #define LSM_COUNT (__end_lsm_info - __start_lsm_info) > @@ -1091,9 +1095,11 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, > const struct qstr *qstr, > const initxattrs initxattrs, void *fs_data) > { > + int i = 0; > + int ret = -EOPNOTSUPP; > struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1]; > struct xattr *lsm_xattr, *evm_xattr, *xattr; > - int ret; > + struct security_hook_list *hook_ptr; > > if (unlikely(IS_PRIVATE(inode))) > return 0; > @@ -1103,15 +1109,26 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, > dir, qstr, NULL, NULL, NULL); > memset(new_xattrs, 0, sizeof(new_xattrs)); > lsm_xattr = new_xattrs; > - ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr, > - &lsm_xattr->name, > - &lsm_xattr->value, > - &lsm_xattr->value_len); > + hlist_for_each_entry(hook_ptr, &security_hook_heads.inode_init_security, > + list) { > + ret = hook_ptr->hook.inode_init_security(inode, dir, qstr, > + &lsm_xattr->name, > + &lsm_xattr->value, > + &lsm_xattr->value_len); > + if (ret == -EOPNOTSUPP) > + continue; This does not work properly. Suppose that you have an LSM with xattr and another without. The final ret will be -EOPNOTSUPP. Instead declare new_xattrs_set boolean, and set to true if ret = 0. After the loop, check the boolean instead of ret. If ret != 0 goto out. > + if (WARN_ON_ONCE(i >= MAX_LSM_EVM_XATTR)) > + ret = -ENOMEM; > + if (ret != 0) > + break; We can check here if the LSM behaved properly, i.e. it set the xattr name and value: if (WARN_ON_ONCE(!lsm_xattr->name || !lsm_xattr->value)) { ret = -ENOMEM; goto out; } > + lsm_xattr++; > + i++; > + } > if (ret) > goto out; > > evm_xattr = lsm_xattr + 1; It should be: evm_xattr = lsm_xattr; You incremented lsm_xattr already, after the LSMs set their xattr. Once you complete the changes, I will send a patch set including your patch with some more patches. Roberto > - ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr); > + ret = evm_inode_init_security(inode, new_xattrs, evm_xattr); > if (ret) > goto out; > ret = initxattrs(inode, new_xattrs, fs_data);
