Hello, Thanks for the review.
On 01/07/26 05:21, Namhyung Kim wrote:
On Fri, Jun 26, 2026 at 09:40:53PM +0530, Tanushree Shah wrote:
The current kallsyms detection in dso__is_kallsyms() uses the
dso_binary_type enum which fixes the issue of kallsyms being cached in
the build-id cache for out-of-tree modules.
However, during build-id injection in perf record/inject, dso_binary_type
has not been explicitly set yet,so dso__binary_type() returns
DSO_BINARY_TYPE__NOT_FOUND instead of DSO_BINARY_TYPE__KALLSYMS for the
kernel DSO. The current check then fails to identify it as kallsyms,
causing build-id symlinks to not be created in ~/.debug/.build-id/ and
perf archive to fail with "Cannot stat" errors.
Steps to reproduce the issue:
1. rm -rf ~/.debug/.build-id
2. perf record sleep 1
3. perf archive
Fix by falling back to matching long_name against the known kallsyms
strings explicitly when binary_type is not yet set
(== DSO_BINARY_TYPE__NOT_FOUND). Use strcmp() for exact matching of
fixed names and strict validation for guest kallsyms with embedded PID
to prevent path traversal attacks.
Fixes: ebf0b332732d ("perf dso: fix dso__is_kallsyms() check")
Signed-off-by: Tanushree Shah <[email protected]>
---
v2 -> v3: Replace strncmp() prefix matching with strcmp() for fixed
kallsyms names and add is_guest_kallsyms_pid_name() to
strictly validate guest kallsyms with PID format, preventing
path traversal attacks.
v1 -> v2: Rename DSO__NAME_GUEST_KALLSYMS to DSO__PREFIX_GUEST_KALLSYMS
to reflect that it is a prefix, not a full name.
v1: https://lore.kernel.org/all/[email protected]/
tools/perf/util/dso.h | 57 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index ede691e9a249..8763e6f65316 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -9,6 +9,7 @@
#include <stdbool.h>
#include <stdio.h>
#include <linux/bitops.h>
+#include <string.h>
#include "build-id.h"
#include "debuginfo.h"
#include "mutex.h"
@@ -20,6 +21,40 @@ struct perf_env;
#define DSO__NAME_KALLSYMS "[kernel.kallsyms]"
#define DSO__NAME_KCORE "[kernel.kcore]"
+#define DSO__NAME_GUEST_KALLSYMS "[guest.kernel.kallsyms]"
+#define DSO__NAME_GUEST_KALLSYMS_PID_PREFIX "[guest.kernel.kallsyms."
+
+/*
+ * Validate names of the form "[guest.kernel.kallsyms.<pid>]", where
+ * <pid> is the PID of the guest VM and varies per guest, so it
+ * cannot be matched with strcmp() against a fixed string.
+ *
+ * Every character after the fixed prefix must be a decimal digit,
+ * with ']' immediately terminating the digit run and nothing
+ * following it. This rules out '/', "..", or any other character
+ * being smuggled into the name.
+ */
+static inline bool is_guest_kallsyms_pid_name(const char *name)
+{
+ const size_t prefix_len = sizeof(DSO__NAME_GUEST_KALLSYMS_PID_PREFIX) -
1;
+ size_t digits;
+
+ if (strncmp(name, DSO__NAME_GUEST_KALLSYMS_PID_PREFIX, prefix_len) != 0)
+ return false;
+
+ digits = strspn(name + prefix_len, "0123456789");
+ if (digits == 0)
+ return false;
+
+ /* ']' must terminate the digit run, with nothing trailing it */
+ if (name[prefix_len + digits] != ']')
+ return false;
+
+ if (name[prefix_len + digits + 1] != '\0')
+ return false;
+
+ return true;
+}
/**
* enum dso_binary_type - The kind of DSO generally associated with a memory
@@ -914,8 +949,28 @@ static inline bool dso__is_kcore(const struct dso *dso)
static inline bool dso__is_kallsyms(const struct dso *dso)
{
enum dso_binary_type bt = dso__binary_type(dso);
I have to check its usage carefully but any chance dso__symtab_type(dso)
instead produces better results?
I did some additional logging and found that symtab_type is not getting
set while running perf record, so it seems dso__symtab_type(dso) would
likely have the same issue here.
+ const char *name;
+
+ if (bt == DSO_BINARY_TYPE__KALLSYMS || bt ==
DSO_BINARY_TYPE__GUEST_KALLSYMS)
+ return true;
+
+ if (bt != DSO_BINARY_TYPE__NOT_FOUND)
+ return false;
+
+ if (!RC_CHK_ACCESS(dso)->kernel)
I think the proper wrapper is dso__kernel().
Thanks for the pointer. Will use this and send v4.
+ return false;
+
+ name = RC_CHK_ACCESS(dso)->long_name;
And dso__long_name().
Sure, will use this and send v4.
Thanks,
Namhyung
+ if (!name)
+ return false;
+
+ if (!strcmp(name, DSO__NAME_KALLSYMS))
+ return true;
+
+ if (!strcmp(name, DSO__NAME_GUEST_KALLSYMS))
+ return true;
- return bt == DSO_BINARY_TYPE__KALLSYMS || bt == DSO_BINARY_TYPE__GUEST_KALLSYMS;
+ return is_guest_kallsyms_pid_name(name);
}
bool dso__is_object_file(const struct dso *dso);
--
2.47.3
Thanks
Tanushree Shah
