[go] io/fs: document that Sub does not check for existence
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Sean Liao (Gerrit)
Feb 6, 2026, 4:08:23 PM (11 hours ago) Feb 6
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Sean Liao has uploaded the change for review![]( "Open in Gerrit")
Commit message
io/fs: document that Sub does not check for existence
Also recommend os.Root for constraining access.
Fixes #77447
Change-Id: Id8d178163438e9264fe19ed37ba03e1ee5d0bd35
Change diff
diff --git a/src/io/fs/sub.go b/src/io/fs/sub.go
index 376d561..63c7a3c 100644
--- a/src/io/fs/sub.go
+++ b/src/io/fs/sub.go
@@ -24,7 +24,8 @@
// Otherwise, Sub returns a new [FS] implementation sub that,
// in effect, implements sub.Open(name) as fsys.Open(path.Join(dir, name)).
// The implementation also translates calls to ReadDir, ReadFile,
-// ReadLink, Lstat, and Glob appropriately.
+// ReadLink, Lstat, and Glob appropriately. Sub does not check if the
+// directory currently exists.
//
// Note that Sub(os.DirFS("/"), "prefix") is equivalent to os.DirFS("/prefix")
// and that neither of them guarantees to avoid operating system
@@ -32,6 +33,7 @@
// does not check for symbolic links inside "/prefix" that point to
// other directories. That is, [os.DirFS] is not a general substitute for a
// chroot-style security mechanism, and Sub does not change that fact.
+// Use [os.Root] to constrain access to particular directory trees.
func Sub(fsys FS, dir string) (FS, error) {
if !ValidPath(dir) {
return nil, &PathError{Op: "sub", Path: dir, Err: ErrInvalid}
Change information
Files:
- M src/io/fs/sub.go
Change size: XS
Delta: 1 file changed, 3 insertions(+), 1 deletion(-)
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Damien Neil (Gerrit)
Feb 6, 2026, 5:52:29 PM (10 hours ago) Feb 6
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Attention needed from Sean Liao
Damien Neil voted and added 1 comment![]( "Open in Gerrit")
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| Code-Review | +2 |
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Michael Pratt (Gerrit)
Feb 6, 2026, 6:22:58 PM (9 hours ago) Feb 6
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Michael Pratt voted Code-Review+1![]( "Open in Gerrit")
| Code-Review | +1 |
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Sean Liao (Gerrit)
Feb 6, 2026, 7:01:57 PM (9 hours ago) Feb 6
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Sean Liao submitted the change![]( "Open in Gerrit")
Change information
Commit message:
io/fs: document that Sub does not check for existence
Also recommend os.Root for constraining access.
Fixes #77447
Change-Id: Id8d178163438e9264fe19ed37ba03e1ee5d0bd35
Reviewed-on: https://go-review.googlesource.com/c/go/+/742284
Reviewed-by: Damien Neil <dn...@google.com>
LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpr...@google.com>
Files:
- M src/io/fs/sub.go
Change size: XS
Delta: 1 file changed, 3 insertions(+), 1 deletion(-)
Branch: refs/heads/master
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Code-Review: +2 by Damien Neil, +1 by Michael Pratt
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