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SubjectRe: [PATCH v5 04/12] ima: Move ima_reset_appraise_flags() call to post hooks
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On Wed, 2021-04-07 at 09:17 -0700, Casey Schaufler wrote:
> > 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),
> > + xvalue->type == EVM_IMA_XATTR_DIGSIG);
> > +}
> > +
>
> Now you're calling ima_protect_xattr() twice for each setxattr.
> Is that safe? Is it performant? Does it matter?

The first time the call to ima_protect_xattr() prevents the
security.ima from being inappropriately modified. The second time it
resets the cached status flags. From a performance perspective,
unnecessarily re-calcuating the file hash is worse than rechecking the
security xattr string.

Mimi

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