[PATCH] capget.2: Correct info about EPERM error

[PATCH] capget.2: Correct info about EPERM error

[Yang Xu]

I see kernel code security/commoncap.c cap_capset function, it only
verifies the new_Effective is a subset of the new_Permitted. It doesn't
verify whether the new_Inheritable is a subset of the new_Permitted.

I found it when I cleanup ltp capset02 test code.

Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
---
 man2/capget.2 | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/man2/capget.2 b/man2/capget.2
index 94d38d877..6cad3d5d8 100644
--- a/man2/capget.2
+++ b/man2/capget.2
@@ -195,8 +195,7 @@ One of the arguments was invalid.
 .TP
 .B EPERM
 An attempt was made to add a capability to the Permitted set, or to set
-a capability in the Effective or Inheritable sets that is not in the
-Permitted set.
+a capability in the Effective sets that is not in the Permitted set.
 .TP
 .B EPERM
 The caller attempted to use
-- 
2.18.0

Re: [PATCH] capget.2: Correct info about EPERM error

[Michael Kerrisk (man-pages)]

Hello Yang Xu,

On 12/12/19 8:23 AM, Yang Xu wrote:
> I see kernel code security/commoncap.c cap_capset function, it only
> verifies the new_Effective is a subset of the new_Permitted. It doesn't
> verify whether the new_Inheritable is a subset of the new_Permitted.
> 
> I found it when I cleanup ltp capset02 test code.
> 
> Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
> ---
>  man2/capget.2 | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/man2/capget.2 b/man2/capget.2
> index 94d38d877..6cad3d5d8 100644
> --- a/man2/capget.2
> +++ b/man2/capget.2
> @@ -195,8 +195,7 @@ One of the arguments was invalid.
>  .TP
>  .B EPERM
>  An attempt was made to add a capability to the Permitted set, or to set
> -a capability in the Effective or Inheritable sets that is not in the
> -Permitted set.
> +a capability in the Effective sets that is not in the Permitted set.
>  .TP
>  .B EPERM
>  The caller attempted to use

Thanks for your note. The manual page is indeed imprecise, but there 
are checks elsewhere (in cap_capset()) that restrict the kinds
of changes that can be made to the inheritable set. I applied
the patch below, which I think correctly captures the details (which
were already described in capabilities(7)).

Thanks,

Michael

diff --git a/man2/capget.2 b/man2/capget.2
index 94d38d877..1d81075ba 100644
--- a/man2/capget.2
+++ b/man2/capget.2
@@ -195,10 +195,22 @@ One of the arguments was invalid.
 .TP
 .B EPERM
 An attempt was made to add a capability to the Permitted set, or to set
-a capability in the Effective or Inheritable sets that is not in the
+a capability in the Effective set that is not in the
 Permitted set.
 .TP
 .B EPERM
+An attempt was made to add a capability to the inheritable set, and either:
+.RS
+.IP * 3
+that capability was not in the caller's bounding set; or
+.IP *
+the capability was not in the caller's permitted set
+and the caller lacked the
+.B CAP_SETPCAP
+capability in its effective set.
+.RE
+.TP
+.B EPERM
 The caller attempted to use
 .BR capset ()
 to modify the capabilities of a thread other than itself,




-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/