modbuildid is never set when kallsyms_lookup_buildid is returning via
successful bpf_address_lookup or ftrace_mod_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@mailbox.org>
---
Changes to v2:
 - Check if CONFIG_STACKTRACE_BUILD_ID is enabled to prevent build fail
Changes to v1:
 - Set modbuildid in ftrace_func_address_lookup

 include/linux/filter.h | 6 ++++--
 include/linux/ftrace.h | 4 ++--
 kernel/kallsyms.c      | 4 ++--
 kernel/trace/ftrace.c  | 8 +++++++-
 4 files changed, 15 insertions(+), 7 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/include/linux/ftrace.h b/include/linux/ftrace.h
index 770f0dc993cc..ed673fa2536b 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -87,11 +87,11 @@ struct ftrace_hash;
 	defined(CONFIG_DYNAMIC_FTRACE)
 int
 ftrace_mod_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);
 #else
 static inline int
 ftrace_mod_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 049e296f586c..b1516d3fa9c5 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -378,11 +378,11 @@ 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,
-						offset, modname, namebuf);
+						offset, modname, modbuildid, namebuf);
 
 	return ret;
 }
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3ec2033c0774..4e4aef987747 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7749,7 +7749,7 @@ ftrace_func_address_lookup(struct ftrace_mod_map *mod_map,
 
 int
 ftrace_mod_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)
 {
 	struct ftrace_mod_map *mod_map;
 	int ret = 0;
@@ -7761,6 +7761,12 @@ ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
 		if (ret) {
 			if (modname)
 				*modname = mod_map->mod->name;
+			if (modbuildid)
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+				*modbuildid = mod_map->mod->build_id;
+#else
+				*modbuildid = NULL;
+#endif
 			break;
 		}
 	}

base-commit: 0048fbb4011ec55c32d3148b2cda56433f273375
-- 
2.50.1

On Wed, 10 Dec 2025 18:03:45 +0100
Maurice Hieronymus <mhi@mailbox.org> wrote:

>  include/linux/filter.h | 6 ++++--
>  include/linux/ftrace.h | 4 ++--
>  kernel/kallsyms.c      | 4 ++--
>  kernel/trace/ftrace.c  | 8 +++++++-
>  4 files changed, 15 insertions(+), 7 deletions(-)

Also split this up into two patches. Then I can take the one for ftrace and
the networking folks can take the bpf update.

-- Steve

On Wed, 10 Dec 2025 18:03:45 +0100
Maurice Hieronymus <mhi@mailbox.org> wrote:

> @@ -7761,6 +7761,12 @@ ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
>  		if (ret) {
>  			if (modname)
>  				*modname = mod_map->mod->name;
> +			if (modbuildid)
> +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)

IS_ENABLED() is for use within C code. This should simply be:

#ifdef CONFIG_STACKTRACE_BUILD_ID

-- Steve

> +				*modbuildid = mod_map->mod->build_id;
> +#else
> +				*modbuildid = NULL;
> +#endif
>  			break;
>  		}
>  	}