diff mbox series

[bpf,v1,1/3] bpf: fix sysfs export of empty BTF section

Message ID b38db205a66238f70823039a8c531535864eaac5.1600417359.git.Tony.Ambardar@gmail.com
State New
Headers show
Series [bpf,v1,1/3] bpf: fix sysfs export of empty BTF section | expand

Commit Message

Tony Ambardar Sept. 20, 2020, 5:01 a.m. UTC 
If BTF data is missing or removed from the ELF section it is still exported
via sysfs as a zero-length file:

  root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
  -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux

Moreover, reads from this file succeed and leak kernel data:

  root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
  000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
  000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
  000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
  002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
  002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|

This situation was first observed with kernel 5.4.x, cross-compiled for a
MIPS target system. Fix by adding a sanity-check for export of zero-length
data sections.

Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---
 kernel/bpf/sysfs_btf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

John Fastabend Sept. 21, 2020, 3:44 p.m. UTC | #1 
Tony Ambardar wrote:
> If BTF data is missing or removed from the ELF section it is still exported

> via sysfs as a zero-length file:

> 

>   root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux

>   -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux

> 

> Moreover, reads from this file succeed and leak kernel data:

> 

>   root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10

>   000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

>   *

>   000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|

>   000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

>   000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|

>   000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|

>   *

>   002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|

>   002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|

>   002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|

> 

> This situation was first observed with kernel 5.4.x, cross-compiled for a

> MIPS target system. Fix by adding a sanity-check for export of zero-length

> data sections.

> 

> Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")

> 

> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>

> ---

>  kernel/bpf/sysfs_btf.c | 6 +++---

>  1 file changed, 3 insertions(+), 3 deletions(-)

> 

> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c

> index 3b495773de5a..11b3380887fa 100644

> --- a/kernel/bpf/sysfs_btf.c

> +++ b/kernel/bpf/sysfs_btf.c

> @@ -30,15 +30,15 @@ static struct kobject *btf_kobj;

>  

>  static int __init btf_vmlinux_init(void)

>  {

> -	if (!__start_BTF)

> +	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;

> +

> +	if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)

>  		return 0;

>  

>  	btf_kobj = kobject_create_and_add("btf", kernel_kobj);

>  	if (!btf_kobj)

>  		return -ENOMEM;

>  

> -	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;

> -

>  	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);

>  }


Thanks LGTM.

Acked-by: John Fastabend <john.fastabend@gmail.com>
Andrii Nakryiko Sept. 21, 2020, 7:21 p.m. UTC | #2 
On Sat, Sep 19, 2020 at 10:05 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
>
> If BTF data is missing or removed from the ELF section it is still exported
> via sysfs as a zero-length file:
>
>   root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
>   -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux
>
> Moreover, reads from this file succeed and leak kernel data:
>
>   root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
>   000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
>   000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
>   000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
>   002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
>   002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|
>
> This situation was first observed with kernel 5.4.x, cross-compiled for a
> MIPS target system. Fix by adding a sanity-check for export of zero-length
> data sections.
>
> Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")
>
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---

Apparently sysfs infrastructure doesn't validate read position and
size when bin_attribute's size is 0, and just expects read callback to
handle such situation explicitly. Preventing sysfs entry from
registering seems like a good solution. Thanks!

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  kernel/bpf/sysfs_btf.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 3b495773de5a..11b3380887fa 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -30,15 +30,15 @@ static struct kobject *btf_kobj;
>
>  static int __init btf_vmlinux_init(void)
>  {
> -       if (!__start_BTF)
> +       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> +
> +       if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
>                 return 0;
>
>         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
>         if (!btf_kobj)
>                 return -ENOMEM;
>
> -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> -
>         return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
>  }
>
> --
> 2.25.1
>
diff mbox series

Patch

diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 3b495773de5a..11b3380887fa 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -30,15 +30,15 @@  static struct kobject *btf_kobj;
 
 static int __init btf_vmlinux_init(void)
 {
-	if (!__start_BTF)
+	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
+
+	if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
 		return 0;
 
 	btf_kobj = kobject_create_and_add("btf", kernel_kobj);
 	if (!btf_kobj)
 		return -ENOMEM;
 
-	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
-
 	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
 }