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sysfs: disallow absolute symlinks #2324

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Sep 27, 2024
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sysfs: disallow absolute symlinks #2324

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6 changes: 6 additions & 0 deletions internal/sysfs/dirfs_supported.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ package sysfs
import (
"io/fs"
"os"
"path"

experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
)
Expand Down Expand Up @@ -34,6 +35,11 @@ func (d *dirFS) Chmod(path string, perm fs.FileMode) experimentalsys.Errno {

// Symlink implements the same method as documented on sys.FS
func (d *dirFS) Symlink(oldName, link string) experimentalsys.Errno {
// Creating a symlink with an absolute path string fails with a "not permitted" error.
// https://github.com/WebAssembly/wasi-filesystem/blob/v0.2.0/path-resolution.md#symlinks
if path.IsAbs(oldName) {
return experimentalsys.EPERM
}
// Note: do not resolve `oldName` relative to this dirFS. The link result is always resolved
// when dereference the `link` on its usage (e.g. readlink, read, etc).
// https://github.com/bytecodealliance/cap-std/blob/v1.0.4/cap-std/src/fs/dir.rs#L404-L409
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1 change: 1 addition & 0 deletions internal/sysfs/dirfs_test.go
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Expand Up @@ -747,6 +747,7 @@ func TestDirFS_Symlink(t *testing.T) {

testFS := DirFS(tmpDir)

require.EqualErrno(t, sys.EPERM, testFS.Symlink("/test.txt", "sub/test.txt"))
require.EqualErrno(t, sys.EEXIST, testFS.Symlink("sub/test.txt", "sub/test.txt"))
// Non-existing old name is allowed.
require.EqualErrno(t, 0, testFS.Symlink("non-existing", "aa"))
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