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Fix off-by-one bug

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This is a fix for https://github.com/docker/for-linux/issues/1012.

The code was not considering that C strings are NULL-terminated so
we need to leave one extra byte.

Without this fix, the testcase in https://github.com/docker/for-linux/issues/1012
fails with

```
Step 61/1001 : RUN echo 60 > 60
 ---> Running in dde85ac3b1e3
Removing intermediate container dde85ac3b1e3
 ---> 80a12a18a241
Step 62/1001 : RUN echo 61 > 61
error creating overlay mount to /23456789112345678921234/overlay2/d368abcc97d6c6ebcf23fa71225e2011d095295d5d8c9b31d6810bea748bdf07-init/merged: no such file or directory
```

with the output of `dmesg -T` as:

```
[Sat Dec 19 02:35:40 2020] overlayfs: failed to resolve '/23456789112345678921234/overlay2/89e435a1b24583c463abb73e8abfad8bf8a88312ef8253455390c5fa0a765517-init/wor': -2
```

with this fix, you get the expected:

```
Step 126/1001 : RUN echo 125 > 125
 ---> Running in 2f2e56da89e0
max depth exceeded
```

Signed-off-by: Oscar Bonilla <6f6231@gmail.com>
This commit is contained in:
Oscar Bonilla 2020-12-20 16:12:27 -08:00
parent b5f863c67e
commit c923f6ac3b
1 changed files with 2 additions and 2 deletions
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4
daemon/graphdriver/overlay2/overlay.go
View file

@ -573,14 +573,14 @@ func (d *Driver) Get(id, mountLabel string) (_ containerfs.ContainerFS, retErr e
// the page size. The mount syscall fails if the mount data cannot
// fit within a page and relative links make the mount data much
// smaller at the expense of requiring a fork exec to chroot.
if len(mountData) > pageSize {
if len(mountData) > pageSize-1 {
if readonly {
opts = indexOff + "lowerdir=" + path.Join(id, diffDirName) + ":" + string(lowers)
} else {
opts = indexOff + "lowerdir=" + string(lowers) + ",upperdir=" + path.Join(id, diffDirName) + ",workdir=" + path.Join(id, workDirName)
}
mountData = label.FormatMountLabel(opts, mountLabel)
if len(mountData) > pageSize {
if len(mountData) > pageSize-1 {
return nil, fmt.Errorf("cannot mount layer, mount label too large %d", len(mountData))
}