[CRIU] [PATCH v2] criu: correctly handle mixed-permission mapped files

[Jamie Liu]

An mmaped file is opened O_RDONLY or O_RDWR depending on the permissions
on the first vma dump_task_mm() encounters mapping that file. This means
that if a file has multiple MAP_SHARED mappings, some of which are
read-only and some of which are read-write, and the first encountered
mapping happens to be read-only, the file will be opened with O_RDONLY
during restore, and mmap(PROT_WRITE) will fail with EACCES.

To fix this, defer filemap open flags selection until restore, since
mapped files are opened per mapping.

Signed-off-by: Jamie Liu <jamieliu at google.com>
---
 cr-dump.c   | 6 +-----
 files-reg.c | 8 ++++++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/cr-dump.c b/cr-dump.c
index 0111115..f7945d9 100644
--- a/cr-dump.c
+++ b/cr-dump.c
@@ -15,7 +15,6 @@
 #include <sys/vfs.h>
 
 #include <sys/sendfile.h>
-#include <sys/mman.h>
 
 #include <sched.h>
 #include <sys/resource.h>
@@ -347,10 +346,7 @@ static int dump_filemap(pid_t pid, struct vma_area *vma_area,
 	BUG_ON(!vma_area->st);
 	p.stat = *vma_area->st;
 
-	if ((vma->prot & PROT_WRITE) && vma_entry_is(vma, VMA_FILE_SHARED))
-		p.flags = O_RDWR;
-	else
-		p.flags = O_RDONLY;
+	/* Flags will be detected during restore in get_filemap_fd() */
 
 	if (fd_id_generate_special(&p.stat, &id))
 		ret = dump_one_reg_file(vma_area->vm_file_fd, id, &p);
diff --git a/files-reg.c b/files-reg.c
index eccd04e..743b035 100644
--- a/files-reg.c
+++ b/files-reg.c
@@ -3,6 +3,7 @@
 #include <errno.h>
 #include <string.h>
 #include <sys/types.h>
+#include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/vfs.h>
 #include <ctype.h>
@@ -708,6 +709,8 @@ int open_reg_by_id(u32 id)
 
 int get_filemap_fd(struct vma_area *vma)
 {
+	struct reg_file_info *rfi;
+
 	/*
 	 * Thevma->fd should have been assigned in collect_filemap
 	 *
@@ -715,6 +718,11 @@ int get_filemap_fd(struct vma_area *vma)
 	 */
 
 	BUG_ON(vma->fd == NULL);
+	rfi = container_of(vma->fd, struct reg_file_info, d);
+	if ((vma->e->prot & PROT_WRITE) && vma_area_is(vma, VMA_FILE_SHARED))
+		rfi->rfe->flags = O_RDWR;
+	else
+		rfi->rfe->flags = O_RDONLY;
 	return open_path(vma->fd, do_open_reg_noseek, NULL);
 }
 
-- 
1.9.1.423.g4596e3a