On Thu, Nov 14, 2019 at 03:47:23PM +0000, Al Viro wrote:
> AFAICS, this
> bytes = (fh->len - offsetof(struct ovl_fh, fid));
> real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
> bytes >> 2, (int)fh->type,
> connected ? ovl_acceptable : NULL, mnt);
> in ovl_decode_real_fh() combined with
> origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
> connected);
> in ovl_check_origin_fh(),
> /* First lookup overlay inode in inode cache by origin fh */
> err = ovl_check_origin_fh(ofs, fh, false, NULL, &stack);
> in ovl_lower_fh_to_d() and
> struct ovl_fh *fh = (struct ovl_fh *) fid;
> ...
> ovl_lower_fh_to_d(sb, fh);
> in ovl_fh_to_dentry() leads to the pointer to struct fid passed to
> exportfs_decode_fh() being 21 bytes ahead of that passed to
> ovl_fh_to_dentry().
>
> However, alignment of struct fid pointers is 32 bits and quite a few
> places dealing with those (including ->fh_to_dentry() instances)
> do access them directly. Argument of ->fh_to_dentry() is supposed
> to be 32bit-aligned, and callers generally guarantee that. Your
> code, OTOH, violates the alignment systematically there - what
> it passes to layers' ->fh_to_dentry() (by way of exportfs_decode_fh())
> always has two lower bits different from what it got itself.
>
> What do we do with that? One solution would be to insert sane padding
> in ovl_fh, but the damn thing appears to be stored as-is in xattrs on
> disk, so that would require rather unpleasant operations reinserting
> the padding on the fly ;-/
Something like this? Totally untested...
Thanks,
Miklos
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index b801c6353100..60a4ca72cb4e 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -253,7 +253,7 @@ struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
BUILD_BUG_ON(MAX_HANDLE_SZ + offsetof(struct ovl_fh, fid) > 255);
fh_len = offsetof(struct ovl_fh, fid) + buflen;
- fh = kmalloc(fh_len, GFP_KERNEL);
+ fh = kzalloc(fh_len, GFP_KERNEL);
if (!fh) {
fh = ERR_PTR(-ENOMEM);
goto out;
@@ -271,7 +271,7 @@ struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
*/
if (is_upper)
fh->flags |= OVL_FH_FLAG_PATH_UPPER;
- fh->len = fh_len;
+ fh->len = fh_len - OVL_FH_WIRE_OFFSET;
fh->uuid = *uuid;
memcpy(fh->fid, buf, buflen);
@@ -300,7 +300,8 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
/*
* Do not fail when upper doesn't support xattrs.
*/
- err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN, fh,
+ err = ovl_check_setxattr(dentry, upper, OVL_XATTR_ORIGIN,
+ fh ? OVL_FH_START(fh) : NULL,
fh ? fh->len : 0, 0);
kfree(fh);
@@ -317,7 +318,8 @@ static int ovl_set_upper_fh(struct dentry *upper, struct dentry *index)
if (IS_ERR(fh))
return PTR_ERR(fh);
- err = ovl_do_setxattr(index, OVL_XATTR_UPPER, fh, fh->len, 0);
+ err = ovl_do_setxattr(index, OVL_XATTR_UPPER,
+ OVL_FH_START(fh), fh->len, 0);
kfree(fh);
return err;
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 73c9775215b3..dedda95c7746 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -234,7 +234,7 @@ static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
if (fh->len > buflen)
goto fail;
- memcpy(buf, (char *)fh, fh->len);
+ memcpy(buf, OVL_FH_START(fh), fh->len);
err = fh->len;
out:
@@ -260,6 +260,7 @@ static int ovl_dentry_to_fh(struct dentry *dentry, u32 *fid, int *max_len)
/* Round up to dwords */
*max_len = (len + 3) >> 2;
+ memset(fid + len, 0, (*max_len << 2) - len);
return OVL_FILEID;
}
@@ -781,7 +782,7 @@ static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
int fh_len, int fh_type)
{
struct dentry *dentry = NULL;
- struct ovl_fh *fh = (struct ovl_fh *) fid;
+ struct ovl_fh *fh = (void *) fid - OVL_FH_WIRE_OFFSET;
int len = fh_len << 2;
unsigned int flags = 0;
int err;
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index e9717c2f7d45..f22a65359df1 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -86,7 +86,8 @@ static int ovl_acceptable(void *ctx, struct dentry *dentry)
*/
int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
{
- if (fh_len < sizeof(struct ovl_fh) || fh_len < fh->len)
+ if (fh_len < sizeof(struct ovl_fh) - OVL_FH_WIRE_OFFSET ||
+ fh_len < fh->len)
return -EINVAL;
if (fh->magic != OVL_FH_MAGIC)
@@ -119,11 +120,11 @@ static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
if (res == 0)
return NULL;
- fh = kzalloc(res, GFP_KERNEL);
+ fh = kzalloc(res + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
if (!fh)
return ERR_PTR(-ENOMEM);
- res = vfs_getxattr(dentry, name, fh, res);
+ res = vfs_getxattr(dentry, name, fh + OVL_FH_WIRE_OFFSET, res);
if (res < 0)
goto fail;
@@ -161,7 +162,7 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
return NULL;
- bytes = (fh->len - offsetof(struct ovl_fh, fid));
+ bytes = (fh->len + OVL_FH_WIRE_OFFSET - offsetof(struct ovl_fh, fid));
real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
bytes >> 2, (int)fh->type,
connected ? ovl_acceptable : NULL, mnt);
@@ -433,7 +434,8 @@ int ovl_verify_set_fh(struct dentry *dentry, const char *name,
err = ovl_verify_fh(dentry, name, fh);
if (set && err == -ENODATA)
- err = ovl_do_setxattr(dentry, name, fh, fh->len, 0);
+ err = ovl_do_setxattr(dentry, name,
+ OVL_FH_START(fh), fh->len, 0);
if (err)
goto fail;
@@ -512,12 +514,12 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
err = -ENOMEM;
len = index->d_name.len / 2;
- fh = kzalloc(len, GFP_KERNEL);
+ fh = kzalloc(len + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
if (!fh)
goto fail;
err = -EINVAL;
- if (hex2bin((u8 *)fh, index->d_name.name, len))
+ if (hex2bin(OVL_FH_START(fh), index->d_name.name, len))
goto fail;
err = ovl_check_fh_len(fh, len);
@@ -603,7 +605,7 @@ static int ovl_get_index_name_fh(struct ovl_fh *fh, struct qstr *name)
if (!n)
return -ENOMEM;
- s = bin2hex(n, fh, fh->len);
+ s = bin2hex(n, OVL_FH_START(fh), fh->len);
*name = (struct qstr) QSTR_INIT(n, s - n);
return 0;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 6934bcf030f0..c62083671a12 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -74,8 +74,13 @@ enum ovl_entry_flag {
/* The type returned by overlay exportfs ops when encoding an ovl_fh handle */
#define OVL_FILEID 0xfb
-/* On-disk and in-memeory format for redirect by file handle */
+#define OVL_FH_WIRE_OFFSET 3
+#define OVL_FH_START(fh) ((void *)(fh) + OVL_FH_WIRE_OFFSET)
struct ovl_fh {
+ /* make sure fid is 32bit aligned */
+ u8 padding[OVL_FH_WIRE_OFFSET];
+
+ /* Wire/xattr encoding begins here*/
u8 version; /* 0 */
u8 magic; /* 0xfb */
u8 len; /* size of this header + size of fid */
