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evm: Implement per signature type decision in security_inode_copy_up_xattr 

To support "portable and immutable signatures" on otherwise unsupported
filesystems, determine the EVM signature type by the content of a file's
xattr. If the file has the appropriate signature type then allow it to be
copied up. All other signature types are discarded as before.

"Portable and immutable" EVM signatures can be copied up by stacked file-
system since the metadata their signature covers does not include file-
system-specific data such as a file's inode number, generation, and UUID.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Stefan Berger 2024-02-23 12:25:06 -05:00 committed by Mimi Zohar
parent 3253804773
commit f2b3fc42f6
1 changed files with 28 additions and 3 deletions
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31
security/integrity/evm/evm_main.c
View File

@ -948,9 +948,34 @@ static void evm_inode_post_setattr(struct mnt_idmap *idmap,
static int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
{
if (strcmp(name, XATTR_NAME_EVM) == 0)
return 1; /* Discard */
return -EOPNOTSUPP;
struct evm_ima_xattr_data *xattr_data = NULL;
int rc;
if (strcmp(name, XATTR_NAME_EVM) != 0)
return -EOPNOTSUPP;
/* first need to know the sig type */
rc = vfs_getxattr_alloc(&nop_mnt_idmap, src, XATTR_NAME_EVM,
(char **)&xattr_data, 0, GFP_NOFS);
if (rc <= 0)
return -EPERM;
if (rc < offsetof(struct evm_ima_xattr_data, type) +
sizeof(xattr_data->type))
return -EPERM;
switch (xattr_data->type) {
case EVM_XATTR_PORTABLE_DIGSIG:
rc = 0; /* allow copy-up */
break;
case EVM_XATTR_HMAC:
case EVM_IMA_XATTR_DIGSIG:
default:
rc = 1; /* discard */
}
kfree(xattr_data);
return rc;
}
/*