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rootfs: only set mode= for tmpfs mount if target already existed

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This was always the intended behaviour but commit 72fbb34f50 ("rootfs:
switch to fd-based handling of mountpoint targets") regressed it when
adding a mechanism to create a file handle to the target if it didn't
already exist (causing the later stat to always succeed).

A lot of people depend on this functionality, so add some tests to make
sure we don't break it in the future.

Fixes: 72fbb34f50 ("rootfs: switch to fd-based handling of mountpoint targets")
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
This commit is contained in:
Aleksa Sarai
2025-11-07 14:52:09 +11:00
parent 95762b6ee1
commit 9a9719eeb4
2 changed files with 93 additions and 13 deletions
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libcontainer/rootfs_linux.go
+12 -13
View File
@@ -513,6 +513,18 @@ func (m *mountEntry) createOpenMountpoint(rootfs string) (Err error) {
_ = dstFile.Close()
}
}()
if err == nil && m.Device == "tmpfs" {
// If the original target exists, copy the mode for the tmpfs mount.
stat, err := dstFile.Stat()
if err != nil {
return fmt.Errorf("check tmpfs source mode: %w", err)
}
dt := fmt.Sprintf("mode=%04o", syscallMode(stat.Mode()))
if m.Data != "" {
dt = dt + "," + m.Data
}
m.Data = dt
}
if err != nil {
if !errors.Is(err, unix.ENOENT) {
return fmt.Errorf("lookup mountpoint target: %w", err)
@@ -553,19 +565,6 @@ func (m *mountEntry) createOpenMountpoint(rootfs string) (Err error) {
}
}
if m.Device == "tmpfs" {
// If the original target exists, copy the mode for the tmpfs mount.
stat, err := dstFile.Stat()
if err != nil {
return fmt.Errorf("check tmpfs source mode: %w", err)
}
dt := fmt.Sprintf("mode=%04o", syscallMode(stat.Mode()))
if m.Data != "" {
dt = dt + "," + m.Data
}
m.Data = dt
}
dstFullPath, err := procfs.ProcSelfFdReadlink(dstFile)
if err != nil {
return fmt.Errorf("get mount destination real path: %w", err)