> From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > Sent: Friday, April 30, 2021 8:00 PM > On Wed, 2021-04-28 at 15:35 +0000, Roberto Sassu wrote: > > > From: Roberto Sassu > > > Sent: Friday, March 5, 2021 4:19 PM > > > ima_inode_setxattr() and ima_inode_removexattr() hooks are called > before > > > an > > > operation is performed. Thus, ima_reset_appraise_flags() should not be > > > called there, as flags might be unnecessarily reset if the operation is > > > denied. > > > > > > This patch introduces the post hooks ima_inode_post_setxattr() and > > > ima_inode_post_removexattr(), and adds the call to > > > ima_reset_appraise_flags() in the new functions. > > > > > > Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > --- > > > fs/xattr.c | 2 ++ > > > include/linux/ima.h | 18 ++++++++++++++++++ > > > security/integrity/ima/ima_appraise.c | 25 ++++++++++++++++++++++--- > > > security/security.c | 1 + > > > 4 files changed, 43 insertions(+), 3 deletions(-) > > > > > > diff --git a/fs/xattr.c b/fs/xattr.c > > > index b3444e06cded..81847f132d26 100644 > > > --- a/fs/xattr.c > > > +++ b/fs/xattr.c > > > @@ -16,6 +16,7 @@ > > > #include <linux/namei.h> > > > #include <linux/security.h> > > > #include <linux/evm.h> > > > +#include <linux/ima.h> > > > #include <linux/syscalls.h> > > > #include <linux/export.h> > > > #include <linux/fsnotify.h> > > > @@ -502,6 +503,7 @@ __vfs_removexattr_locked(struct > user_namespace > > > *mnt_userns, > > > > > > if (!error) { > > > fsnotify_xattr(dentry); > > > + ima_inode_post_removexattr(dentry, name); > > > evm_inode_post_removexattr(dentry, name); > > > } > > > > > > diff --git a/include/linux/ima.h b/include/linux/ima.h > > > index 61d5723ec303..5e059da43857 100644 > > > --- a/include/linux/ima.h > > > +++ b/include/linux/ima.h > > > @@ -171,7 +171,13 @@ extern void ima_inode_post_setattr(struct > > > user_namespace *mnt_userns, > > > struct dentry *dentry); > > > extern int ima_inode_setxattr(struct dentry *dentry, const char > *xattr_name, > > > const void *xattr_value, size_t xattr_value_len); > > > +extern void ima_inode_post_setxattr(struct dentry *dentry, > > > + const char *xattr_name, > > > + const void *xattr_value, > > > + size_t xattr_value_len); > > > extern int ima_inode_removexattr(struct dentry *dentry, const char > > > *xattr_name); > > > +extern void ima_inode_post_removexattr(struct dentry *dentry, > > > + const char *xattr_name); > > > #else > > > static inline bool is_ima_appraise_enabled(void) > > > { > > > @@ -192,11 +198,23 @@ static inline int ima_inode_setxattr(struct > dentry > > > *dentry, > > > return 0; > > > } > > > > > > +static inline void ima_inode_post_setxattr(struct dentry *dentry, > > > + const char *xattr_name, > > > + const void *xattr_value, > > > + size_t xattr_value_len) > > > +{ > > > +} > > > + > > > static inline int ima_inode_removexattr(struct dentry *dentry, > > > const char *xattr_name) > > > { > > > return 0; > > > } > > > + > > > +static inline void ima_inode_post_removexattr(struct dentry *dentry, > > > + const char *xattr_name) > > > +{ > > > +} > > > #endif /* CONFIG_IMA_APPRAISE */ > > > > > > #if defined(CONFIG_IMA_APPRAISE) && > > > defined(CONFIG_INTEGRITY_TRUSTED_KEYRING) > > > diff --git a/security/integrity/ima/ima_appraise.c > > > b/security/integrity/ima/ima_appraise.c > > > index 565e33ff19d0..1f029e4c8d7f 100644 > > > --- a/security/integrity/ima/ima_appraise.c > > > +++ b/security/integrity/ima/ima_appraise.c > > > @@ -577,21 +577,40 @@ int ima_inode_setxattr(struct dentry *dentry, > const > > > char *xattr_name, > > > if (result == 1) { > > > if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST)) > > > return -EINVAL; > > > - ima_reset_appraise_flags(d_backing_inode(dentry), > > > - xvalue->type == EVM_IMA_XATTR_DIGSIG); > > > result = 0; > > > } > > > return result; > > > } > > > > > > +void ima_inode_post_setxattr(struct dentry *dentry, const char > > > *xattr_name, > > > + const void *xattr_value, size_t xattr_value_len) > > > +{ > > > + const struct evm_ima_xattr_data *xvalue = xattr_value; > > > + int result; > > > + > > > + result = ima_protect_xattr(dentry, xattr_name, xattr_value, > > > + xattr_value_len); > > > + if (result == 1) > > > + ima_reset_appraise_flags(d_backing_inode(dentry), > > > > I found an issue in this patch. > > > > Moving ima_reset_appraise_flags() to the post hook causes this > > function to be executed also when __vfs_setxattr_noperm() is > > called. > > > > The problem is that at the end of a write IMA calls > > ima_collect_measurement() to recalculate the file digest and > > update security.ima. ima_collect_measurement() sets > > IMA_COLLECTED. > > > > However, after that __vfs_setxattr_noperm() causes > > IMA_COLLECTED to be reset, and to unnecessarily recalculate > > the file digest. This wouldn't happen if ima_reset_appraise_flags() > > is in the pre hook. > > > > I solved by replacing: > > iint->flags &= ~IMA_DONE_MASK; > > with: > > iint->flags &= ~(IMA_DONE_MASK & ~IMA_COLLECTED); > > > > just when the IMA_CHANGE_XATTR bit is set. It should > > not be a problem since setting an xattr does not influence > > the file content. > > > > Mimi, what do you think? > > Thank yor for noticing this. > > Without seeing the actual change it is hard to tell. The only place > that "iint->flags &= ~IMA_DONE_MASK;" occurs is in neither of the above > functions, but in process_measurement(). There it is a part of a > compound "if" statement. Perhaps it would be ok to change it for just > the IMA_CHANGE_XATTR test, but definitely not for the other conditions, > like untrusted mounts. Ok. Should I include this change in this patch or in a separate patch? > Moving ima_reset_appraise_flags() to the post hooks is to minimize > resetting the flags unnecessarily. That is really a performance fix, > not something necessary for making the EVM portable & immutable > signatures more usable. As much as possible, please minimize the > changes to facilitate review and testing. Ok. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > thanks, > > Mimi
