From 51b4c35bb38b7df4af24de7f103863dd79129b01 Mon Sep 17 00:00:00 2001
From: Tobias Stoeckmann <tobias@stoeckmann.org>
Date: Tue, 27 May 2025 17:09:12 +0200
Subject: [PATCH] Fix FILE_skip regression

The fseek* family of functions return 0 on success, not the new offset.
This is only true for lseek.

Fixes https://github.com/libarchive/libarchive/issues/2641
Fixes dcbf1e0ededa95849f098d154a25876ed5754bcf

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>

CVE: CVE-2025-5918
Upstream-Status: Backport [https://github.com/libarchive/libarchive/commit/51b4c35bb38b7df4af24de7f103863dd79129b01]
Signed-off-by: Peter Marko <peter.marko@siemens.com>
---
 libarchive/archive_read_open_file.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/libarchive/archive_read_open_file.c b/libarchive/archive_read_open_file.c
index 6ed18a0c..742923ab 100644
--- a/libarchive/archive_read_open_file.c
+++ b/libarchive/archive_read_open_file.c
@@ -133,7 +133,7 @@ FILE_skip(struct archive *a, void *client_data, int64_t request)
 #else
 	long skip = (long)request;
 #endif
-	int64_t old_offset, new_offset;
+	int64_t old_offset, new_offset = -1;
 	int skip_bits = sizeof(skip) * 8 - 1;
 
 	(void)a; /* UNUSED */
@@ -171,11 +171,14 @@ FILE_skip(struct archive *a, void *client_data, int64_t request)
 #ifdef __ANDROID__
 			new_offset = lseek(fileno(mine->f), skip, SEEK_CUR);
 #elif HAVE__FSEEKI64
-			new_offset = _fseeki64(mine->f, skip, SEEK_CUR);
+			if (_fseeki64(mine->f, skip, SEEK_CUR) == 0)
+				new_offset = _ftelli64(mine->f);
 #elif HAVE_FSEEKO
-			new_offset = fseeko(mine->f, skip, SEEK_CUR);
+			if (fseeko(mine->f, skip, SEEK_CUR) == 0)
+				new_offset = ftello(mine->f);
 #else
-			new_offset = fseek(mine->f, skip, SEEK_CUR);
+			if (fseek(mine->f, skip, SEEK_CUR) == 0)
+				new_offset = ftell(mine->f);
 #endif
 			if (new_offset >= 0)
 				return (new_offset - old_offset);
