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From: Anthony G. Basile <blueness@gentoo.org>
This patch adds support for a restricted user-controlled namespace on
tmpfs filesystem used to house PaX flags. The namespace must be of the
form user.pax.* and its value cannot exceed a size of 8 bytes.
This is needed even on all Gentoo systems so that XATTR_PAX flags
are preserved for users who might build packages using portage on
a tmpfs system with a non-hardened kernel and then switch to a
hardened kernel with XATTR_PAX enabled.
The namespace is added to any user with Extended Attribute support
enabled for tmpfs. Users who do not enable xattrs will not have
the XATTR_PAX flags preserved.
diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h
index e4629b9..6958086 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -63,3 +63,8 @@
#endif /* __KERNEL__ */
+
+/* User namespace */
+#define XATTR_PAX_PREFIX XATTR_USER_PREFIX "pax."
+#define XATTR_PAX_FLAGS_SUFFIX "flags"
+#define XATTR_NAME_PAX_FLAGS XATTR_PAX_PREFIX XATTR_PAX_FLAGS_SUFFIX
#endif /* _UAPI_LINUX_XATTR_H */
diff --git a/mm/shmem.c b/mm/shmem.c
index 1c44af7..f23bb1b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2201,6 +2201,7 @@ static const struct xattr_handler *shmem_xattr_handlers[] = {
static int shmem_xattr_validate(const char *name)
{
struct { const char *prefix; size_t len; } arr[] = {
+ { XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN},
{ XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN },
{ XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN }
};
@@ -2256,7 +2257,14 @@ static int shmem_setxattr(struct dentry *dentry, const char *name,
if (err)
return err;
+
+ if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
+ if (strcmp(name, XATTR_NAME_PAX_FLAGS))
+ return -EOPNOTSUPP;
+ if (size > 8)
+ return -EINVAL;
+ }
if (size == 0)
value = ""; /* empty EA, do not remove */
return shmem_xattr_set(dentry, name, value, size, flags);
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