[Cluster-devel] [PATCH dlm-next 2/2] fs: dlm: transparently align name buffer

[Alexander Aring <aahringo@redhat.com>]

This patch adds a zeroed temporary buffer to align the given resource
name of a dlm lock user space request transparently to a 4 byte aligned
buffer. I hit the assert while running the recent pending patch which
contains a 4 byte aligned assert for the dlm header msglength field.
It's important that the allocation and msglength field is 4 byte aligned
as the dlm_header structure is natural aligned to 4 byte values. The
internal dlm allocator can return the next remaining space from a
previously allocated length. The buffer will not be aligned to 4 byte
anymore if this case occurs. At receiving side we cannot parse the next
dlm message because the next dlm header starts at a unaligned address as
well.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---
 fs/dlm/user.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/dlm/user.c b/fs/dlm/user.c
index 9f2f743eeb31..70a5116df9fe 100644
--- a/fs/dlm/user.c
+++ b/fs/dlm/user.c
@@ -236,6 +236,7 @@ void dlm_user_add_ast(struct dlm_lkb *lkb, uint32_t flags, int mode,
 static int device_user_lock(struct dlm_user_proc *proc,
 			    struct dlm_lock_params *params)
 {
+	unsigned char name[DLM_RESNAME_MAXLEN] = {};
 	struct dlm_ls *ls;
 	struct dlm_user_args *ua;
 	uint32_t lkid;
@@ -270,17 +271,19 @@ static int device_user_lock(struct dlm_user_proc *proc,
 				         params->lkid, params->lvb,
 					 (unsigned long) params->timeout);
 	} else if (params->flags & DLM_LKF_ORPHAN) {
+		memcpy(name, params->name, params->namelen);
 		error = dlm_user_adopt_orphan(ls, ua,
 					 params->mode, params->flags,
-					 params->name, params->namelen,
+					 name, ALIGN(params->namelen, 4),
 					 (unsigned long) params->timeout,
 					 &lkid);
 		if (!error)
 			error = lkid;
 	} else {
+		memcpy(name, params->name, params->namelen);
 		error = dlm_user_request(ls, ua,
 					 params->mode, params->flags,
-					 params->name, params->namelen,
+					 name, ALIGN(params->namelen, 4),
 					 (unsigned long) params->timeout);
 		if (!error)
 			error = ua->lksb.sb_lkid;
-- 
2.26.2