[PATCH 4.2.y-ckt 20/98] Fix directory hardlinks from deleted directories

Kamal Mostafa
2016-03-15T23:32:15Z

From: David Woodhouse <David.Woodhouse@intel.com>

commit be629c62a603e5935f8177fd8a19e014100a259e upstream.

When a directory is deleted, we don't take too much care about killing off
all the dirents that belong to it — on the basis that on remount, the scan
will conclude that the directory is dead anyway.

This doesn't work though, when the deleted directory contained a child
directory which was moved *out*. In the early stages of the fs build
we can then end up with an apparent hard link, with the child directory
appearing both in its true location, and as a child of the original
directory which are this stage of the mount process we don't *yet* know
is defunct.

To resolve this, take out the early special-casing of the "directories
shall not have hard links" rule in jffs2_build_inode_pass1(), and let the
normal nlink processing happen for directories as well as other inodes.

Then later in the build process we can set ic->pino_nlink to the parent
inode#, as is required for directories during normal operaton, instead
of the nlink. And complain only *then* about hard links which are still
in evidence even after killing off all the unreachable paths.

Reported-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/jffs2/build.c | 75 ++++++++++++++++++++++++++++++++++++++++-------------
fs/jffs2/nodelist.h | 6 ++++-
2 files changed, 62 insertions(+), 19 deletions(-)

diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
index a3750f9..c1f0494 100644
--- a/fs/jffs2/build.c
+++ b/fs/jffs2/build.c
@@ -49,7 +49,8 @@ next_inode(int *i, struct jffs2_inode_cache *ic, struct jffs2_sb_info *c)

static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
- struct jffs2_inode_cache *ic)
+ struct jffs2_inode_cache *ic,
+ int *dir_hardlinks)
{
struct jffs2_full_dirent *fd;

@@ -68,19 +69,21 @@ static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
dbg_fsbuild("child \"%s\" (ino #%u) of dir ino #%u doesn't exist!\n",
fd->name, fd->ino, ic->ino);
jffs2_mark_node_obsolete(c, fd->raw);
+ /* Clear the ic/raw union so it doesn't cause problems later. */
+ fd->ic = NULL;
continue;
}

+ /* From this point, fd->raw is no longer used so we can set fd->ic */
+ fd->ic = child_ic;
+ child_ic->pino_nlink++;
+ /* If we appear (at this stage) to have hard-linked directories,
+ * set a flag to trigger a scan later */
if (fd->type == DT_DIR) {
- if (child_ic->pino_nlink) {
- JFFS2_ERROR("child dir \"%s\" (ino #%u) of dir ino #%u appears to be a hard link\n",
- fd->name, fd->ino, ic->ino);
- /* TODO: What do we do about it? */
- } else {
- child_ic->pino_nlink = ic->ino;
- }
- } else
- child_ic->pino_nlink++;
+ child_ic->flags |= INO_FLAGS_IS_DIR;
+ if (child_ic->pino_nlink > 1)
+ *dir_hardlinks = 1;
+ }

dbg_fsbuild("increased nlink for child \"%s\" (ino #%u)\n", fd->name, fd->ino);
/* Can't free scan_dents so far. We might need them in pass 2 */
@@ -94,8 +97,7 @@ static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
*/
static int jffs2_build_filesystem(struct jffs2_sb_info *c)
{
- int ret;
- int i;
+ int ret, i, dir_hardlinks = 0;
struct jffs2_inode_cache *ic;
struct jffs2_full_dirent *fd;
struct jffs2_full_dirent *dead_fds = NULL;
@@ -119,7 +121,7 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
/* Now scan the directory tree, increasing nlink according to every dirent found. */
for_each_inode(i, c, ic) {
if (ic->scan_dents) {
- jffs2_build_inode_pass1(c, ic);
+ jffs2_build_inode_pass1(c, ic, &dir_hardlinks);
cond_resched();
}
}
@@ -155,6 +157,20 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
}

dbg_fsbuild("pass 2a complete\n");
+
+ if (dir_hardlinks) {
+ /* If we detected directory hardlinks earlier, *hopefully*
+ * they are gone now because some of the links were from
+ * dead directories which still had some old dirents lying
+ * around and not yet garbage-collected, but which have
+ * been discarded above. So clear the pino_nlink field
+ * in each directory, so that the final scan below can
+ * print appropriate warnings. */
+ for_each_inode(i, c, ic) {
+ if (ic->flags & INO_FLAGS_IS_DIR)
+ ic->pino_nlink = 0;
+ }
+ }
dbg_fsbuild("freeing temporary data structures\n");

/* Finally, we can scan again and free the dirent structs */
@@ -162,6 +178,33 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
while(ic->scan_dents) {
fd = ic->scan_dents;
ic->scan_dents = fd->next;
+ /* We do use the pino_nlink field to count nlink of
+ * directories during fs build, so set it to the
+ * parent ino# now. Now that there's hopefully only
+ * one. */
+ if (fd->type == DT_DIR) {
+ if (!fd->ic) {
+ /* We'll have complained about it and marked the coresponding
+ raw node obsolete already. Just skip it. */
+ continue;
+ }
+
+ /* We *have* to have set this in jffs2_build_inode_pass1() */
+ BUG_ON(!(fd->ic->flags & INO_FLAGS_IS_DIR));
+
+ /* We clear ic->pino_nlink ∀ directories' ic *only* if dir_hardlinks
+ * is set. Otherwise, we know this should never trigger anyway, so
+ * we don't do the check. And ic->pino_nlink still contains the nlink
+ * value (which is 1). */
+ if (dir_hardlinks && fd->ic->pino_nlink) {
+ JFFS2_ERROR("child dir \"%s\" (ino #%u) of dir ino #%u is also hard linked from dir ino #%u\n",
+ fd->name, fd->ino, ic->ino, fd->ic->pino_nlink);
+ /* Should we unlink it from its previous parent? */
+ }
+
+ /* For directories, ic->pino_nlink holds that parent inode # */
+ fd->ic->pino_nlink = ic->ino;
+ }
jffs2_free_full_dirent(fd);
}
ic->scan_dents = NULL;
@@ -240,11 +283,7 @@ static void jffs2_build_remove_unlinked_inode(struct jffs2_sb_info *c,

/* Reduce nlink of the child. If it's now zero, stick it on the
dead_fds list to be cleaned up later. Else just free the fd */
-
- if (fd->type == DT_DIR)
- child_ic->pino_nlink = 0;
- else
- child_ic->pino_nlink--;
+ child_ic->pino_nlink--;

if (!child_ic->pino_nlink) {
dbg_fsbuild("inode #%u (\"%s\") now has no links; adding to dead_fds list.\n",
diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
index fa35ff7..0637271 100644
--- a/fs/jffs2/nodelist.h
+++ b/fs/jffs2/nodelist.h
@@ -194,6 +194,7 @@ struct jffs2_inode_cache {
#define INO_STATE_CLEARING 6 /* In clear_inode() */

#define INO_FLAGS_XATTR_CHECKED 0x01 /* has no duplicate xattr_ref */
+#define INO_FLAGS_IS_DIR 0x02 /* is a directory */

#define RAWNODE_CLASS_INODE_CACHE 0
#define RAWNODE_CLASS_XATTR_DATUM 1
@@ -249,7 +250,10 @@ struct jffs2_readinode_info

struct jffs2_full_dirent
{
- struct jffs2_raw_node_ref *raw;
+ union {
+ struct jffs2_raw_node_ref *raw;
+ struct jffs2_inode_cache *ic; /* Just during part of build */
+ };
struct jffs2_full_dirent *next;
uint32_t version;
uint32_t ino; /* == zero for unlink */
--
2.7.0