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evm: add support to disable EVM on unsupported filesystems 

Identify EVM unsupported filesystems by defining a new flag
SB_I_EVM_UNSUPPORTED.

Don't verify, write, remove or update 'security.evm' on unsupported
filesystems.

Acked-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Mimi Zohar 2023-12-18 08:06:40 -05:00
parent 40ca4ee313
commit cd708c938f
2 changed files with 35 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/fs.h
View File

@ -1164,6 +1164,7 @@ extern int send_sigurg(struct fown_struct *fown);
#define SB_I_USERNS_VISIBLE 0x00000010 /* fstype already mounted */
#define SB_I_IMA_UNVERIFIABLE_SIGNATURE 0x00000020
#define SB_I_UNTRUSTED_MOUNTER 0x00000040
#define SB_I_EVM_UNSUPPORTED 0x00000080
#define SB_I_SKIP_SYNC 0x00000100 /* Skip superblock at global sync */
#define SB_I_PERSB_BDI 0x00000200 /* has a per-sb bdi */

35
security/integrity/evm/evm_main.c
View File

@ -151,6 +151,17 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
return count;
}
static int is_unsupported_fs(struct dentry *dentry)
{
struct inode *inode = d_backing_inode(dentry);
if (inode->i_sb->s_iflags & SB_I_EVM_UNSUPPORTED) {
pr_info_once("%s not supported\n", inode->i_sb->s_type->name);
return 1;
}
return 0;
}
/*
* evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
*
@ -181,6 +192,9 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
return iint->evm_status;
if (is_unsupported_fs(dentry))
return INTEGRITY_UNKNOWN;
/* if status is not PASS, try to check again - against -ENOMEM */
/* first need to know the sig type */
@ -408,6 +422,9 @@ enum integrity_status evm_verifyxattr(struct dentry *dentry,
if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
return INTEGRITY_UNKNOWN;
if (is_unsupported_fs(dentry))
return INTEGRITY_UNKNOWN;
if (!iint) {
iint = integrity_iint_find(d_backing_inode(dentry));
if (!iint)
@ -491,15 +508,21 @@ static int evm_protect_xattr(struct mnt_idmap *idmap,
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (is_unsupported_fs(dentry))
return -EPERM;
} else if (!evm_protected_xattr(xattr_name)) {
if (!posix_xattr_acl(xattr_name))
return 0;
if (is_unsupported_fs(dentry))
return 0;
evm_status = evm_verify_current_integrity(dentry);
if ((evm_status == INTEGRITY_PASS) ||
(evm_status == INTEGRITY_NOXATTRS))
return 0;
goto out;
}
} else if (is_unsupported_fs(dentry))
return 0;
evm_status = evm_verify_current_integrity(dentry);
if (evm_status == INTEGRITY_NOXATTRS) {
@ -750,6 +773,9 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
if (!(evm_initialized & EVM_INIT_HMAC))
return;
if (is_unsupported_fs(dentry))
return;
evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
}
@ -814,8 +840,12 @@ int evm_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
return 0;
if (is_unsupported_fs(dentry))
return 0;
if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
return 0;
evm_status = evm_verify_current_integrity(dentry);
/*
* Writing attrs is safe for portable signatures, as portable signatures
@ -859,6 +889,9 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
if (!(evm_initialized & EVM_INIT_HMAC))
return;
if (is_unsupported_fs(dentry))
return;
if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
evm_update_evmxattr(dentry, NULL, NULL, 0);
}