udf: prevent speculative execution

CVE-2017-5753 (Spectre v1 Intel)

Since the eahd->appAttrLocation value in function
udf_add_extendedattr() seems to be controllable by
userspace and later on conditionally (upon bound check)
used in following memmove, insert an observable speculation
barrier before its usage. This should prevent
observable speculation on that branch and avoid
kernel memory leak.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/fs/udf/misc.c b/fs/udf/misc.c
index 71d1c25f360d170286862382cb4cf0e31cf40508..aee498e52b7b5000304ce8e471b601d330dc69c4 100644 (file)
--- a/fs/udf/misc.c
+++ b/fs/udf/misc.c
@@ -104,6 +104,8 @@ struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
                                        iinfo->i_lenEAttr) {
                                uint32_t aal =
                                        le32_to_cpu(eahd->appAttrLocation);
+
+                               osb();
                                memmove(&ea[offset - aal + size],
                                        &ea[aal], offset - aal);
                                offset -= aal;
@@ -114,6 +116,8 @@ struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
                                        iinfo->i_lenEAttr) {
                                uint32_t ial =
                                        le32_to_cpu(eahd->impAttrLocation);
+
+                               osb();
                                memmove(&ea[offset - ial + size],
                                        &ea[ial], offset - ial);
                                offset -= ial;
@@ -125,6 +129,8 @@ struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
                                        iinfo->i_lenEAttr) {
                                uint32_t aal =
                                        le32_to_cpu(eahd->appAttrLocation);
+
+                               osb();
                                memmove(&ea[offset - aal + size],
                                        &ea[aal], offset - aal);
                                offset -= aal;