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files-reg: try dump_ghost_remap if link-remap failed with error ENOENT

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An issue with dumping deleted reg files in overlayfs:

After deleting a file originated from lower layer in merged dir,
fstat() on the /proc/$pid/map_files symlink returns st_nlink=1, while
linkat() fails with errno ENOENT.

Signed-off-by: langyenan <ianlang@tencent.com>
This commit is contained in:
ianlang 2021-12-03 15:15:30 +08:00 committed by Andrei Vagin
parent 14075baf72
commit d57f27bc94
2 changed files with 40 additions and 6 deletions
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42
criu/files-reg.c
View File

@ -959,7 +959,25 @@ void free_link_remaps(void)
}
static int linkat_hard(int odir, char *opath, int ndir, char *npath, uid_t uid, gid_t gid, int flags);
static int create_link_remap(char *path, int len, int lfd, u32 *idp, struct ns_id *nsid, const struct stat *st)
static void check_overlayfs_fallback(char *path, const struct fd_parms *parms, bool *fallback)
{
if (!fallback || parms->fs_type != OVERLAYFS_SUPER_MAGIC)
return;
/*
* In overlayFS, linkat() fails with ENOENT if the removed file is
* originated from lower layer. The cause of failure is that linkat()
* sees the file has st_nlink=0, which is different than st_nlink=1 we
* got from earlier fstat() on lfd. By setting *fb=true, we will fall
* back to dump_ghost_remap() as it is what should have been done to
* removed files with st_nlink=0.
*/
pr_info("Unable to link-remap %s on overlayFS, fall back to dump_ghost_remap\n", path);
*fallback = true;
}
static int create_link_remap(char *path, int len, int lfd, u32 *idp, struct ns_id *nsid, const struct fd_parms *parms,
bool *fallback)
{
char link_name[PATH_MAX], *tmp;
FileEntry fe = FILE_ENTRY__INIT;
@ -967,6 +985,7 @@ static int create_link_remap(char *path, int len, int lfd, u32 *idp, struct ns_i
FownEntry fwn = FOWN_ENTRY__INIT;
int mntns_root;
int ret;
const struct stat *ost = &parms->stat;
if (!opts.link_remap_ok) {
pr_err("Can't create link remap for %s. "
@ -1005,11 +1024,12 @@ static int create_link_remap(char *path, int len, int lfd, u32 *idp, struct ns_i
mntns_root = mntns_get_root_fd(nsid);
again:
ret = linkat_hard(lfd, "", mntns_root, link_name, st->st_uid, st->st_gid, AT_EMPTY_PATH);
ret = linkat_hard(lfd, "", mntns_root, link_name, ost->st_uid, ost->st_gid, AT_EMPTY_PATH);
if (ret < 0 && errno == ENOENT) {
/* Use grand parent, if parent directory does not exist. */
if (trim_last_parent(link_name) < 0) {
pr_err("trim failed: @%s@\n", link_name);
check_overlayfs_fallback(path, parms, fallback);
return -1;
}
goto again;
@ -1028,12 +1048,13 @@ again:
return pb_write_one(img_from_set(glob_imgset, CR_FD_FILES), &fe, PB_FILE);
}
static int dump_linked_remap(char *path, int len, const struct stat *ost, int lfd, u32 id, struct ns_id *nsid)
static int dump_linked_remap(char *path, int len, const struct fd_parms *parms, int lfd, u32 id, struct ns_id *nsid,
bool *fallback)
{
u32 lid;
RemapFilePathEntry rpe = REMAP_FILE_PATH_ENTRY__INIT;
if (create_link_remap(path, len, lfd, &lid, nsid, ost))
if (create_link_remap(path, len, lfd, &lid, nsid, parms, fallback))
return -1;
rpe.orig_id = id;
@ -1150,6 +1171,7 @@ static int check_path_remap(struct fd_link *link, const struct fd_parms *parms,
struct stat pst;
const struct stat *ost = &parms->stat;
int flags = 0;
bool fallback = false;
if (parms->fs_type == PROC_SUPER_MAGIC) {
/* The file points to /proc/pid/<foo> where pid is a dead
@ -1239,7 +1261,7 @@ static int check_path_remap(struct fd_link *link, const struct fd_parms *parms,
* links on it) to have some persistent name at hands.
*/
pr_debug("Dump silly-rename linked remap for %x\n", id);
return dump_linked_remap(rpath + 1, plen - 1, ost, lfd, id, nsid);
return dump_linked_remap(rpath + 1, plen - 1, parms, lfd, id, nsid, NULL);
}
mntns_root = mntns_get_root_fd(nsid);
@ -1260,7 +1282,15 @@ static int check_path_remap(struct fd_link *link, const struct fd_parms *parms,
if (errno == ENOENT) {
link_strip_deleted(link);
return dump_linked_remap(rpath + 1, plen - 1, ost, lfd, id, nsid);
ret = dump_linked_remap(rpath + 1, plen - 1, parms, lfd, id, nsid, &fallback);
if (ret < 0 && fallback) {
/* fallback is true only if following conditions are true:
* 1. linkat() inside dump_linked_remap() failed with ENOENT
* 2. parms->fs_type == overlayFS
*/
return dump_ghost_remap(rpath + 1, ost, lfd, id, nsid);
}
return ret;
}
pr_perror("Can't stat path");

4
criu/include/fs-magic.h
View File

@ -53,4 +53,8 @@
#define AUTOFS_SUPER_MAGIC 0x0187
#endif
#ifndef OVERLAYFS_SUPER_MAGIC
#define OVERLAYFS_SUPER_MAGIC 0x794c7630
#endif
#endif /* __CR_FS_MAGIC_H__ */