On Sat, 2022-11-05 at 07:06 -0400, Paul Moore wrote: > On Wed, Oct 26, 2022 at 10:30 AM Nicolas Bouchinet > <nicolas.bouchinet@xxxxxxxxxxx> 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/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)) > > ... > > > @@ -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; > > + if (WARN_ON_ONCE(i >= MAX_LSM_EVM_XATTR)) > > + ret = -ENOMEM; > > It would really like to see us get rid of the MAX_LSM_EVM_XATTR macro > and determine the array size similar to what we do with the security > blob sizes. The macro definition is a kludgy hack that is bound to > get out of sync at some point and this extra checking inside the hook > is something we should work to remove. In this case, I already implemented this, as it was originally suggested by Casey. I will resend this: https://lore.kernel.org/linux-integrity/20210427113732.471066-1-roberto.sassu@xxxxxxxxxx/ with few minor tweaks. Roberto > > + if (ret != 0) > > + break; > > + lsm_xattr++; > > + i++; > > + } > > if (ret) > > goto out; > > > > evm_xattr = lsm_xattr + 1; > > - 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); > > -- > > 2.38.1
