> From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > Sent: Monday, August 24, 2020 2:18 PM > On Thu, 2020-06-18 at 18:04 +0200, Roberto Sassu wrote: > > When EVM_ALLOW_METADATA_WRITES is set, EVM allows any operation > on > > metadata. Its main purpose is to allow users to freely set metadata when > > they are protected by a portable signature, until the HMAC key is loaded. > > > > However, IMA is not notified about metadata changes and, after the first > > appraisal, always allows access to the files without checking metadata > > again. > > ^after the first successful appraisal > > > > This patch checks in evm_reset_status() if EVM_ALLOW_METADATA > WRITES is > > enabled and if it is, sets the IMA_CHANGE_XATTR/ATTR bits depending on > the > > operation performed. At the next appraisal, metadata are revalidated. > > EVM modifying IMA bits crosses the boundary between EVM and IMA. > There > is already an IMA post_setattr hook. IMA could reset its own bit > there. If necessary EVM could export as a function it's status info. I wouldn't try to guess in IMA when EVM resets its status. We would have to duplicate the logic to check if an EVM key is loaded, if the passed xattr is a POSIX ACL, ... I think it is better to set a flag, maybe a new one, directly in EVM, to notify the integrity subsystem that iint->evm_status is no longer valid. If the EVM flag is set, IMA would reset the appraisal flags, as it uses iint->evm_status for appraisal. We can consider to reset also the measure flags when we have a template that includes file metadata. Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > Mimi > > > > > This patch also adds a call to evm_reset_status() in > > evm_inode_post_setattr() so that EVM won't return the cached status > the > > next time appraisal is performed. > > > > Cc: stable@xxxxxxxxxxxxxxx # 4.16.x > > Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of > EVM-protected metadata") > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > --- > > security/integrity/evm/evm_main.c | 14 ++++++++++---- > > 1 file changed, 10 insertions(+), 4 deletions(-) > > > > diff --git a/security/integrity/evm/evm_main.c > b/security/integrity/evm/evm_main.c > > index 41cc6a4aaaab..d4d918183094 100644 > > --- a/security/integrity/evm/evm_main.c > > +++ b/security/integrity/evm/evm_main.c > > @@ -478,13 +478,17 @@ int evm_inode_removexattr(struct dentry > *dentry, const char *xattr_name) > > return evm_protect_xattr(dentry, xattr_name, NULL, 0); > > } > > > > -static void evm_reset_status(struct inode *inode) > > +static void evm_reset_status(struct inode *inode, int bit) > > { > > struct integrity_iint_cache *iint; > > > > iint = integrity_iint_find(inode); > > - if (iint) > > + if (iint) { > > + if (evm_initialized & EVM_ALLOW_METADATA_WRITES) > > + set_bit(bit, &iint->atomic_flags); > > + > > iint->evm_status = INTEGRITY_UNKNOWN; > > + } > > } > > > > /**:q > > @@ -507,7 +511,7 @@ void evm_inode_post_setxattr(struct dentry > *dentry, const char *xattr_name, > > && !posix_xattr_acl(xattr_name))) > > return; > > > > - evm_reset_status(dentry->d_inode); > > + evm_reset_status(dentry->d_inode, IMA_CHANGE_XATTR); > > > > evm_update_evmxattr(dentry, xattr_name, xattr_value, > xattr_value_len); > > } > > @@ -527,7 +531,7 @@ void evm_inode_post_removexattr(struct dentry > *dentry, const char *xattr_name) > > if (!evm_key_loaded() || !evm_protected_xattr(xattr_name)) > > return; > > > > - evm_reset_status(dentry->d_inode); > > + evm_reset_status(dentry->d_inode, IMA_CHANGE_XATTR); > > > > evm_update_evmxattr(dentry, xattr_name, NULL, 0); > > } > > @@ -600,6 +604,8 @@ void evm_inode_post_setattr(struct dentry > *dentry, int ia_valid) > > if (!evm_key_loaded()) > > return; > > > > + evm_reset_status(dentry->d_inode, IMA_CHANGE_ATTR); > > + > > if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) > > evm_update_evmxattr(dentry, NULL, NULL, 0); > > } >
