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
For #75677
Fixes #75711

Change-Id: I70b907b584a7b8676df8a149a1db728ae681a770
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/2800
Reviewed-by: Roland Shoemaker <[email protected]>
Reviewed-by: Nicholas Husin <[email protected]>
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/2987
Reviewed-by: Damien Neil <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/709852
TryBot-Bypass: Michael Pratt <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>

This is a port of upstream commit 2612dcfd3cb6dd73c76e14a24fe1a68e2708e4e3 ,
"Copyright 2009 The Go Authors."

Signed-off-by: Miloslav Trmač <[email protected]>

Port a fix for CVE-2025-58183