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package syscallcompat
import (
"path/filepath"
"strings"
"syscall"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// OpenNofollow opens the file/dir at "relPath" in a way that is secure against
// symlink attacks. Symlinks that are part of "relPath" are never followed.
// This function is implemented by walking the directory tree, starting at
// "baseDir", using the Openat syscall with the O_NOFOLLOW flag.
// Symlinks that are part of the "baseDir" path are followed.
func OpenNofollow(baseDir string, relPath string, flags int, mode uint32) (fd int, err error) {
if !filepath.IsAbs(baseDir) {
tlog.Warn.Printf("BUG: OpenNofollow called with relative baseDir=%q", baseDir)
return -1, syscall.EINVAL
}
if filepath.IsAbs(relPath) {
tlog.Warn.Printf("BUG: OpenNofollow called with absolute relPath=%q", relPath)
return -1, syscall.EINVAL
}
// Open the base dir
dirfd, err := syscall.Open(baseDir, syscall.O_RDONLY, 0)
if err != nil {
return -1, err
}
// Caller wanted to open baseDir itself?
if relPath == "" {
return dirfd, nil
}
// Split the path into components and separate intermediate directories
// and the final basename
parts := strings.Split(relPath, "/")
dirs := parts[:len(parts)-1]
final := parts[len(parts)-1]
// Walk intermediate directories
var dirfd2 int
for _, name := range dirs {
dirfd2, err = Openat(dirfd, name, syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
syscall.Close(dirfd)
if err != nil {
return -1, err
}
dirfd = dirfd2
}
defer syscall.Close(dirfd)
// Open the final component with the flags and permissions requested by
// the user plus forced NOFOLLOW.
return Openat(dirfd, final, flags|syscall.O_NOFOLLOW, mode)
}
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