perf tools: Fix uninitialized pathname on uncompressed fallback in filename__decompress()

filename__decompress() has an early return path for files that are not
actually compressed.  This path returns the fd from open() directly but
never writes to the pathname output parameter, leaving the caller with
an uninitialized buffer despite a successful return.

Callers like dso__decompress_kmodule_path() pass pathname to
decompress_kmodule() which uses it to set the decompressed file path.
If pathname is uninitialized, subsequent operations on the path produce
undefined behavior.

Fix by setting pathname to an empty string on the uncompressed path.
Callers already check for an empty pathname to distinguish temporary
decompressed files (which need unlink) from the original file.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Fixes: 7ac22b088afe26a4 ("perf tools: Add filename__decompress function")
Cc: Jiri Olsa <jolsa@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

4 files changed, 23 insertions, 9 deletions

diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
index 47043a3a2fb4..e82ecdc95777 100644
--- a/tools/perf/tests/code-reading.c
+++ b/tools/perf/tests/code-reading.c
@@ -471,8 +471,11 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
 			goto out;
 		}
 
-		decomp = true;
-		objdump_name = decomp_name;
+		/* empty pathname means file wasn't actually compressed */
+		if (decomp_name[0] != '\0') {
+			decomp = true;
+			objdump_name = decomp_name;
+		}
 	}
 
 	/* Read the object code using objdump */
diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
index 59ba88e1f744..0a1a7e9cf3ef 100644
--- a/tools/perf/util/disasm.c
+++ b/tools/perf/util/disasm.c
@@ -1577,8 +1577,11 @@ int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
 		if (dso__decompress_kmodule_path(dso, symfs_filename, tmp, sizeof(tmp)) < 0)
 			return -1;
 
-		decomp = true;
-		strcpy(symfs_filename, tmp);
+		/* empty pathname means file wasn't actually compressed */
+		if (tmp[0] != '\0') {
+			decomp = true;
+			strcpy(symfs_filename, tmp);
+		}
 	}
 
 	/*
diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index ee06a252a54d..6a34717c9f31 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -343,8 +343,11 @@ int filename__decompress(const char *name, char *pathname,
 	 * To keep this transparent, we detect this and return the file
 	 * descriptor to the uncompressed file.
 	 */
-	if (!compressions[comp].is_compressed(name))
+	if (!compressions[comp].is_compressed(name)) {
+		if (pathname && len > 0)
+			pathname[0] = '\0';
 		return open(name, O_RDONLY | O_CLOEXEC);
+	}
 
 	fd = mkostemp(tmpbuf, O_CLOEXEC);
 	if (fd < 0) {
@@ -598,8 +601,11 @@ static char *dso__get_filename(struct dso *dso, const char *root_dir,
 			goto out;
 		}
 
-		*decomp = true;
-		strcpy(name, newpath);
+		/* empty pathname means file wasn't actually compressed */
+		if (newpath[0] != '\0') {
+			*decomp = true;
+			strcpy(name, newpath);
+		}
 	}
 	return name;
 
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 06cfb84f86eb..10902a5dc6db 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -920,12 +920,14 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
 			return -1;
 		}
 		close(fd);
-		filename = path;
+		/* non-empty path means a temp file was created */
+		if (path[0] != '\0')
+			filename = path;
 	}
 
 	err = read_build_id(filename, bid);
 
-	if (m.comp)
+	if (m.comp && filename == path)
 		unlink(filename);
 	return err;
 }