Re: [PATCH v4 2/2] kallsyms: Always initialize modbuildid on bpf address

[Alexei Starovoitov]

On Sat, Dec 20, 2025 at 8:19 AM Maurice Hieronymus <mhi@xxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxx>
> ---
>  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)

No.
Please search the earlier threads where this was discussed.
The patches to fix this were posted and I think they landed
in some tree already.

pw-bot: cr