linux-kernel - Re: [PATCH stable 6.1 v3] lib/buildid: Handle memfd_secret() files in build_id

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Message-ID: <Z9f29SF5Wg5wA7FC@krava>
Date: Mon, 17 Mar 2025 11:18:29 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Chen Linxuan <chenlinxuan@...pin.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, Sasha Levin <sashal@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Yi Lai <yi1.lai@...el.com>, Daniel Borkmann <daniel@...earbox.net>,
	stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH stable 6.1 v3] lib/buildid: Handle memfd_secret() files
 in build_id_parse()

On Mon, Mar 17, 2025 at 01:23:00PM +0800, Chen Linxuan wrote:
> [ Upstream commit 5ac9b4e935dfc6af41eee2ddc21deb5c36507a9f ]
> 
> >From memfd_secret(2) manpage:
> 
>   The memory areas backing the file created with memfd_secret(2) are
>   visible only to the processes that have access to the file descriptor.
>   The memory region is removed from the kernel page tables and only the
>   page tables of the processes holding the file descriptor map the
>   corresponding physical memory. (Thus, the pages in the region can't be
>   accessed by the kernel itself, so that, for example, pointers to the
>   region can't be passed to system calls.)
> 
> We need to handle this special case gracefully in build ID fetching
> code. Return -EFAULT whenever secretmem file is passed to build_id_parse()
> family of APIs. Original report and repro can be found in [0].
> 
>   [0] https://lore.kernel.org/bpf/ZwyG8Uro%2FSyTXAni@ly-workstation/
> 
> Fixes: de3ec364c3c3 ("lib/buildid: add single folio-based file reader abstraction")
> Reported-by: Yi Lai <yi1.lai@...el.com>
> Suggested-by: Shakeel Butt <shakeel.butt@...ux.dev>
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
> Link: https://lore.kernel.org/bpf/20241017175431.6183-A-hca@linux.ibm.com
> Link: https://lore.kernel.org/bpf/20241017174713.2157873-1-andrii@kernel.org
> [ Chen Linxuan: backport same logic without folio-based changes ]
> Cc: stable@...r.kernel.org
> Fixes: 88a16a130933 ("perf: Add build id data in mmap2 event")
> Signed-off-by: Chen Linxuan <chenlinxuan@...pin.org>

lgtm

Reviewed-by: Jiri Olsa <jolsa@...nel.org>

jirka


> ---
> v1 -> v2: use vma_is_secretmem() instead of directly checking
>           vma->vm_file->f_op == &secretmem_fops
> v2 -> v3: keep original comment
> ---
>  lib/buildid.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/lib/buildid.c b/lib/buildid.c
> index 9fc46366597e..8d839ff5548e 100644
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -5,6 +5,7 @@
>  #include <linux/elf.h>
>  #include <linux/kernel.h>
>  #include <linux/pagemap.h>
> +#include <linux/secretmem.h>
>  
>  #define BUILD_ID 3
>  
> @@ -157,6 +158,10 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
>  	if (!vma->vm_file)
>  		return -EINVAL;
>  
> +	/* reject secretmem folios created with memfd_secret() */
> +	if (vma_is_secretmem(vma))
> +		return -EFAULT;
> +
>  	page = find_get_page(vma->vm_file->f_mapping, 0);
>  	if (!page)
>  		return -EFAULT;	/* page not mapped */
> -- 
> 2.48.1
>