EVM might update the evm xattr while the VFS performs a remount to
readonly mode. This is not properly checked for, additionally check
the s_readonly_remount superblock flag before writing.
The bug can for example be observed with UBIFS. UBIFS checks the free
space on the device before and after a remount. With EVM enabled the
free space sometimes differs between both checks.
Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
---
security/integrity/evm/evm_main.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index a8d502827270..4a147a998aa7 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -185,6 +185,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
iint->flags |= EVM_IMMUTABLE_DIGSIG;
evm_status = INTEGRITY_PASS_IMMUTABLE;
} else if (!IS_RDONLY(d_backing_inode(dentry)) &&
+ !(dentry->d_inode->i_sb->s_readonly_remount) &&
!IS_IMMUTABLE(d_backing_inode(dentry))) {
evm_update_evmxattr(dentry, xattr_name,
xattr_value,
--
2.16.1
