Documentation
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Overview ¶
Package tar is a drop-in replacement for archive/tar with security focus.
To prevent security implications (e.g. directory traversal) of attacker controlled crafted tar archives, this library sanitizes - file names (bugos filename entries like ../something are fixed on the fly) - the file mode (removing special bits like setuid) It also: - skips special file types silently (fifos, device nodes, char devices, etc.) - strips extended file system attributes - skips files that would need to be extracted through a symbolic link
Features turned on by default: - SanitizeFilenames - PreventSymlinkTraversal These two features are compatible with all known legitimate use-cases.
You may enable the other features individually like this: tr := tar.NewReader(buf) tr.SetSecurityMode(tr.GetSecurityMode() | tar.SanitizeFileMode | tar.DropXattrs) or tr.SetSecurityMode(tar.MaximumSecurityMode)
You may opt out from a certain feature like this: tr.SetSecurityMode(tr.GetSecurityMode() &^ tar.SanitizeFileMode)
Notes about PreventSymlinkTraversal. Consider the following archive: $ tar tvf traverse-via-links.tar lrwxrwxrwx username/groupname 0 2023-03-08 09:43 linktoroot -> / -rw-rw-r-- username/groupname 5 2023-03-08 09:44 linktoroot/root/.bashrc
If an archive like this is extracted blindly, the .bashrc file of the root user would be overwritten. The safearchive/tar library prevents this by keeping track of symbolic links and not emitting entries that would need to be extracted through a symbolic link. This is a feature enabled by default (PreventSymlinkTraversal), as no legitimate archives should contain entries that are to be extracted through a symbolic link.
Index ¶
Constants ¶
const ( // FormatUnknown indicates that the format is unknown. // @see archive/tar.FormatUnknown FormatUnknown = tar.FormatUnknown // FormatUSTAR represents the USTAR header format defined in POSIX.1-1988. // @see archive/tar.FormatUSTAR FormatUSTAR = tar.FormatUSTAR // FormatPAX represents the PAX header format defined in POSIX.1-2001. // @see archive/tar.FormatPAX FormatPAX = tar.FormatPAX // FormatGNU represents the GNU header format. // @see archive/tar.FormatGNU FormatGNU = tar.FormatGNU )
const ( // Type '0' indicates a regular file. TypeReg = tar.TypeReg TypeRegA = tar.TypeRegA // Deprecated: Use TypeReg instead. // Type '1' to '6' are header-only flags and may not have a data body. TypeLink = tar.TypeLink // Hard link TypeSymlink = tar.TypeSymlink // Symbolic link TypeChar = tar.TypeChar // Character device node TypeBlock = tar.TypeBlock // Block device node TypeDir = tar.TypeDir // Directory TypeFifo = tar.TypeFifo // FIFO node // Type '7' is reserved. TypeCont = tar.TypeCont // Type 'x' is used by the PAX format to store key-value records that // are only relevant to the next file. // This package transparently handles these types. TypeXHeader = tar.TypeXHeader // Type 'g' is used by the PAX format to store key-value records that // are relevant to all subsequent files. // This package only supports parsing and composing such headers, // but does not currently support persisting the global state across files. TypeXGlobalHeader = tar.TypeXGlobalHeader // Type 'S' indicates a sparse file in the GNU format. TypeGNUSparse = tar.TypeGNUSparse // Types 'L' and 'K' are used by the GNU format for a meta file // used to store the path or link name for the next file. // This package transparently handles these types. TypeGNULongName = tar.TypeGNULongName TypeGNULongLink = tar.TypeGNULongLink )
Type flags for Header.Typeflag.
const DefaultSecurityMode = SanitizeFilenames | PreventSymlinkTraversal
DefaultSecurityMode is a set of security features that are enabled by default.
const MaximumSecurityMode = SkipSpecialFiles | SanitizeFileMode | SanitizeFilenames | PreventSymlinkTraversal | DropXattrs
MaximumSecurityMode enables all features for maximum security. Recommended for integrations that need file contents only (and nothing unix specific).
Variables ¶
var ( // ErrHeader invalid tar header ErrHeader = tar.ErrHeader // ErrWriteTooLong write too long ErrWriteTooLong = tar.ErrWriteTooLong // ErrFieldTooLong header field too long ErrFieldTooLong = tar.ErrFieldTooLong // ErrWriteAfterClose write after close ErrWriteAfterClose = tar.ErrWriteAfterClose )
Functions ¶
Types ¶
type Format ¶
Format represents the tar archive format.
The original tar format was introduced in Unix V7. Since then, there have been multiple competing formats attempting to standardize or extend the V7 format to overcome its limitations. The most common formats are the USTAR, PAX, and GNU formats, each with their own advantages and limitations.
The following table captures the capabilities of each format:
| USTAR | PAX | GNU ------------------+--------+-----------+---------- Name | 256B | unlimited | unlimited Linkname | 100B | unlimited | unlimited Size | uint33 | unlimited | uint89 Mode | uint21 | uint21 | uint57 Uid/Gid | uint21 | unlimited | uint57 Uname/Gname | 32B | unlimited | 32B ModTime | uint33 | unlimited | int89 AccessTime | n/a | unlimited | int89 ChangeTime | n/a | unlimited | int89 Devmajor/Devminor | uint21 | uint21 | uint57 ------------------+--------+-----------+---------- string encoding | ASCII | UTF-8 | binary sub-second times | no | yes | no sparse files | no | yes | yes
The table's upper portion shows the Header fields, where each format reports the maximum number of bytes allowed for each string field and the integer type used to store each numeric field (where timestamps are stored as the number of seconds since the Unix epoch).
The table's lower portion shows specialized features of each format, such as supported string encodings, support for sub-second timestamps, or support for sparse files.
The Writer currently provides no support for sparse files.
type Header ¶
A Header represents a single header in a tar archive. Some fields may not be populated.
For forward compatibility, users that retrieve a Header from Reader.Next, mutate it in some ways, and then pass it back to Writer.WriteHeader should do so by creating a new Header and copying the fields that they are interested in preserving.
func FileInfoHeader ¶
FileInfoHeader creates a partially-populated Header from fi. If fi describes a symlink, FileInfoHeader records link as the link target. If fi describes a directory, a slash is appended to the name.
Since fs.FileInfo's Name method only returns the base name of the file it describes, it may be necessary to modify Header.Name to provide the full path name of the file.
type Reader ¶
type Reader struct {
// contains filtered or unexported fields
}
Reader provides sequential access to the contents of a tar archive. Reader.Next advances to the next file in the archive (including the first), and then Reader can be treated as an io.Reader to access the file's data.
func (*Reader) GetSecurityMode ¶
func (tr *Reader) GetSecurityMode() SecurityMode
GetSecurityMode returns the currently enabled security features
func (*Reader) Next ¶
Next advances to the next entry in the tar archive. The Header.Size determines how many bytes can be read for the next file. Any remaining data in the current file is automatically discarded.
io.EOF is returned at the end of the input.
func (*Reader) Read ¶
Read reads from the current file in the tar archive. It returns (0, io.EOF) when it reaches the end of that file, until Next is called to advance to the next file.
If the current file is sparse, then the regions marked as a hole are read back as NUL-bytes.
Calling Read on special types like TypeLink, TypeSymlink, TypeChar, TypeBlock, TypeDir, and TypeFifo returns (0, io.EOF) regardless of what the Header.Size claims.
func (*Reader) SetSecurityMode ¶
func (tr *Reader) SetSecurityMode(s SecurityMode)
SetSecurityMode controls the security features applied when reading this tar archive
type SecurityMode ¶
type SecurityMode int
SecurityMode controls security features to enforce
const ( // SkipSpecialFiles security mode skips special files (e.g. block devices or fifos) SkipSpecialFiles SecurityMode = 1 // SanitizeFileMode will drop special file modes (e.g. setuid and tmp bit) SanitizeFileMode SecurityMode = 2 // SanitizeFilenames will sanitize filenames (dropping .. path components and turning entries into relative) // The very first version (early 2022) of this library featured this security measure only. SanitizeFilenames SecurityMode = 4 // DropXattrs will drop extended attributes from the header DropXattrs SecurityMode = 16 // PreventSymlinkTraversal drops malicious entries that attempt to write to an outside location // through a symbolic link. PreventSymlinkTraversal SecurityMode = 32 )
Source Files