archive/tar: set a limit on the size of GNU sparse file 1.0 regions

Sparse files in tar archives contain only the non-zero components
of the file. There are several different encodings for sparse
files. When reading GNU tar pax 1.0 sparse files, archive/tar did
not set a limit on the size of the sparse region data. A malicious
archive containing a large number of sparse blocks could cause
archive/tar to read an unbounded amount of data from the archive
into memory.

Since a malicious input can be highly compressable, a small
compressed input could cause very large allocations.

Cap the size of the sparse block data to the same limit used
for PAX headers (1 MiB).

Thanks to Harshit Gupta (Mr HAX) (https://www.linkedin.com/in/iam-harshit-gupta/)
for reporting this issue.

Fixes CVE-2025-58183
Fixes #75677

Change-Id: I70b907b584a7b8676df8a149a1db728ae681a770
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/2800
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/709861
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Bypass: Michael Pratt <mpratt@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/archive/tar/reader_test.go b/src/archive/tar/reader_test.go
index 99340a3047..fca53dae74 100644
--- a/src/archive/tar/reader_test.go
+++ b/src/archive/tar/reader_test.go
@@ -621,6 +621,11 @@ func TestReader(t *testing.T) {
 			},
 			Format: FormatPAX,
 		}},
+	}, {
+		// Small compressed file that uncompresses to
+		// a file with a very large GNU 1.0 sparse map.
+		file: "testdata/gnu-sparse-many-zeros.tar.bz2",
+		err:  errSparseTooLong,
 	}}
 
 	for _, v := range vectors {