linux-kernel - [PATCH v4 2/2] kallsyms: Always initialize modbuildid on bpf address

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Message-ID: <20251220181838.63242-3-mhi@mailbox.org>
Date: Sat, 20 Dec 2025 19:18:38 +0100
From: Maurice Hieronymus <mhi@...lbox.org>
To: ast@...nel.org,
	daniel@...earbox.net,
	john.fastabend@...il.com,
	andrii@...nel.org,
	martin.lau@...ux.dev,
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Cc: georges.aureau@....com,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	mhi@...lbox.org
Subject: [PATCH v4 2/2] kallsyms: Always initialize modbuildid on bpf address

modbuildid is never set when kallsyms_lookup_buildid is returning via
successful bpf_address_lookup.

This leads to an uninitialized pointer dereference on x86 when
CONFIG_STACKTRACE_BUILD_ID=y inside __sprint_symbol.

Prevent this by always initializing modbuildid.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220717
Signed-off-by: Maurice Hieronymus <mhi@...lbox.org>
---
 include/linux/filter.h | 6 ++++--
 kernel/kallsyms.c      | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index fd54fed8f95f..eb1d1c876503 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1384,12 +1384,14 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr);
 
 static inline int
 bpf_address_lookup(unsigned long addr, unsigned long *size,
-		   unsigned long *off, char **modname, char *sym)
+		   unsigned long *off, char **modname, const unsigned char **modbuildid, char *sym)
 {
 	int ret = __bpf_address_lookup(addr, size, off, sym);
 
 	if (ret && modname)
 		*modname = NULL;
+	if (ret && modbuildid)
+		*modbuildid = NULL;
 	return ret;
 }
 
@@ -1455,7 +1457,7 @@ static inline struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
 
 static inline int
 bpf_address_lookup(unsigned long addr, unsigned long *size,
-		   unsigned long *off, char **modname, char *sym)
+		   unsigned long *off, char **modname, const unsigned char **modbuildid, char *sym)
 {
 	return 0;
 }
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 5ca69eafda7a..b1516d3fa9c5 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -378,7 +378,7 @@ static int kallsyms_lookup_buildid(unsigned long addr,
 				    modname, modbuildid, namebuf);
 	if (!ret)
 		ret = bpf_address_lookup(addr, symbolsize,
-					 offset, modname, namebuf);
+					 offset, modname, modbuildid, namebuf);
 
 	if (!ret)
 		ret = ftrace_mod_address_lookup(addr, symbolsize,
-- 
2.50.1