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std.tar: add support for file path in pax attributes
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Handles .extended_header type to parse PAX attributes and check if they override
the path of the next file. Increases file path limit to std.fs.MAX_PATH_BYTES.

Fixes #15342
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@189900 @Vexu
189900 authored and Vexu committed Sep 8, 2023
1 parent fa46750 commit 39a98dc
Showing 1 changed file with 137 additions and 40 deletions.
177 changes: 137 additions & 40 deletions lib/std/tar.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ pub const Header = struct {
/// Return value may point into Header buffer, or might point into the
/// argument buffer.
/// TODO: check against "../" and other nefarious things
pub fn fullFileName(header: Header, buffer: *[255]u8) ![]const u8 {
pub fn fullFileName(header: Header, buffer: *[std.fs.MAX_PATH_BYTES]u8) ![]const u8 {
const n = name(header);
if (!is_ustar(header))
return n;
Expand Down Expand Up @@ -83,6 +83,44 @@ pub const Header = struct {
}
};

const Buffer = struct {
buffer: [512 * 8]u8 = undefined,
start: usize = 0,
end: usize = 0,

pub fn readChunk(b: *Buffer, reader: anytype, count: usize) ![]const u8 {
b.ensureCapacity(1024);

const ask = @min(b.buffer.len - b.end, count -| (b.end - b.start));
b.end += try reader.readAtLeast(b.buffer[b.end..], ask);

return b.buffer[b.start..b.end];
}

pub fn advance(b: *Buffer, count: usize) void {
b.start += count;
assert(b.start <= b.end);
}

pub fn skip(b: *Buffer, reader: anytype, count: usize) !void {
if (b.start + count > b.end) {
try reader.skipBytes(b.start + count - b.end, .{});
b.start = b.end;
} else {
b.advance(count);
}
}

inline fn ensureCapacity(b: *Buffer, count: usize) void {
if (b.buffer.len - b.start < count) {
const dest_end = b.end - b.start;
@memcpy(b.buffer[0..dest_end], b.buffer[b.start..b.end]);
b.end = dest_end;
b.start = 0;
}
}
};

pub fn pipeToFileSystem(dir: std.fs.Dir, reader: anytype, options: Options) !void {
switch (options.mode_mode) {
.ignore => {},
Expand All @@ -95,30 +133,27 @@ pub fn pipeToFileSystem(dir: std.fs.Dir, reader: anytype, options: Options) !voi
@panic("TODO: unimplemented: tar ModeMode.executable_bit_only");
},
}
var file_name_buffer: [255]u8 = undefined;
var buffer: [512 * 8]u8 = undefined;
var start: usize = 0;
var end: usize = 0;
var file_name_buffer: [std.fs.MAX_PATH_BYTES]u8 = undefined;
var file_name_override_len: usize = 0;
var buffer: Buffer = .{};
header: while (true) {
if (buffer.len - start < 1024) {
const dest_end = end - start;
@memcpy(buffer[0..dest_end], buffer[start..end]);
end = dest_end;
start = 0;
}
const ask_header = @min(buffer.len - end, 1024 -| (end - start));
end += try reader.readAtLeast(buffer[end..], ask_header);
switch (end - start) {
const chunk = try buffer.readChunk(reader, 1024);
switch (chunk.len) {
0 => return,
1...511 => return error.UnexpectedEndOfStream,
else => {},
}
const header: Header = .{ .bytes = buffer[start..][0..512] };
start += 512;
buffer.advance(512);

const header: Header = .{ .bytes = chunk[0..512] };
const file_size = try header.fileSize();
const rounded_file_size = std.mem.alignForward(u64, file_size, 512);
const pad_len = @as(usize, @intCast(rounded_file_size - file_size));
const unstripped_file_name = try header.fullFileName(&file_name_buffer);
const unstripped_file_name = if (file_name_override_len > 0)
file_name_buffer[0..file_name_override_len]
else
try header.fullFileName(&file_name_buffer);
file_name_override_len = 0;
switch (header.fileType()) {
.directory => {
const file_name = try stripComponents(unstripped_file_name, options.strip_components);
Expand All @@ -138,36 +173,59 @@ pub fn pipeToFileSystem(dir: std.fs.Dir, reader: anytype, options: Options) !voi

var file_off: usize = 0;
while (true) {
if (buffer.len - start < 1024) {
const dest_end = end - start;
@memcpy(buffer[0..dest_end], buffer[start..end]);
end = dest_end;
start = 0;
}
// Ask for the rounded up file size + 512 for the next header.
// TODO: https://github.com/ziglang/zig/issues/14039
const ask = @as(usize, @intCast(@min(
buffer.len - end,
rounded_file_size + 512 - file_off -| (end - start),
)));
end += try reader.readAtLeast(buffer[end..], ask);
if (end - start < ask) return error.UnexpectedEndOfStream;
// TODO: https://github.com/ziglang/zig/issues/14039
const slice = buffer[start..@as(usize, @intCast(@min(file_size - file_off + start, end)))];
const temp = try buffer.readChunk(reader, @intCast(rounded_file_size + 512 - file_off));
if (temp.len == 0) return error.UnexpectedEndOfStream;
const slice = temp[0..@as(usize, @intCast(@min(file_size - file_off, temp.len)))];
try file.writeAll(slice);

file_off += slice.len;
start += slice.len;
buffer.advance(slice.len);
if (file_off >= file_size) {
start += pad_len;
// Guaranteed since we use a buffer divisible by 512.
assert(start <= end);
buffer.advance(pad_len);
continue :header;
}
}
},
.global_extended_header, .extended_header => {
if (start + rounded_file_size > end) return error.TarHeadersTooBig;
start = @as(usize, @intCast(start + rounded_file_size));
.extended_header => {
if (file_size == 0) {
buffer.advance(@intCast(rounded_file_size));
continue;
}

const chunk_size: usize = @intCast(rounded_file_size + 512);
var data_off: usize = 0;
file_name_override_len = while (data_off < file_size) {
const slice = try buffer.readChunk(reader, chunk_size - data_off);
if (slice.len == 0) return error.UnexpectedEndOfStream;
const remaining_size: usize = @intCast(file_size - data_off);
const attr_info = try parsePaxAttribute(slice[0..@min(remaining_size, slice.len)], remaining_size);

if (std.mem.eql(u8, attr_info.key, "path")) {
if (attr_info.value_len > file_name_buffer.len) return error.NameTooLong;
buffer.advance(attr_info.value_off);
data_off += attr_info.value_off;
break attr_info.value_len;
}

try buffer.skip(reader, attr_info.size);
data_off += attr_info.size;
} else 0;

var i: usize = 0;
while (i < file_name_override_len) {
const slice = try buffer.readChunk(reader, chunk_size - data_off - i);
if (slice.len == 0) return error.UnexpectedEndOfStream;
const copy_size: usize = @intCast(@min(file_name_override_len - i, slice.len));
@memcpy(file_name_buffer[i .. i + copy_size], slice[0..copy_size]);
buffer.advance(copy_size);
i += copy_size;
}

try buffer.skip(reader, @intCast(rounded_file_size - data_off - file_name_override_len));
continue :header;
},
.global_extended_header => {
buffer.skip(reader, @intCast(rounded_file_size)) catch return error.TarHeadersTooBig;
},
.hard_link => return error.TarUnsupportedFileType,
.symbolic_link => return error.TarUnsupportedFileType,
Expand Down Expand Up @@ -196,5 +254,44 @@ test stripComponents {
try expectEqualStrings("c", try stripComponents("a/b/c", 2));
}

const PaxAttributeInfo = struct {
size: usize,
key: []const u8,
value_off: usize,
value_len: usize,
};

fn parsePaxAttribute(data: []const u8, max_size: usize) !PaxAttributeInfo {
const pos_space = std.mem.indexOfScalar(u8, data, ' ') orelse return error.InvalidPaxAttribute;
const pos_equals = std.mem.indexOfScalarPos(u8, data, pos_space, '=') orelse return error.InvalidPaxAttribute;
const kv_size = try std.fmt.parseInt(usize, data[0..pos_space], 10);
if (kv_size > max_size) {
return error.InvalidPaxAttribute;
}
return .{
.size = kv_size,
.key = data[pos_space + 1 .. pos_equals],
.value_off = pos_equals + 1,
.value_len = kv_size - pos_equals - 2,
};
}

test parsePaxAttribute {
const expectEqual = std.testing.expectEqual;
const expectEqualStrings = std.testing.expectEqualStrings;
const expectError = std.testing.expectError;
const prefix = "1011 path=";
const file_name = "0123456789" ** 100;
const header = prefix ++ file_name ++ "\n";
const attr_info = try parsePaxAttribute(header, 1011);
try expectEqual(@as(usize, 1011), attr_info.size);
try expectEqualStrings("path", attr_info.key);
try expectEqual(prefix.len, attr_info.value_off);
try expectEqual(file_name.len, attr_info.value_len);
try expectEqual(attr_info, try parsePaxAttribute(header, 1012));
try expectError(error.InvalidPaxAttribute, parsePaxAttribute(header, 1010));
try expectError(error.InvalidPaxAttribute, parsePaxAttribute("", 0));
}

const std = @import("std.zig");
const assert = std.debug.assert;

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