Re: BUG at security/selinux/avc.c:883 (was: Re: linux-next: Treefor July 17: early crash on x86-64)

[Stephen Smalley]

On Sun, 2008-07-20 at 13:15 +0100, Al Viro wrote:
> On Sun, Jul 20, 2008 at 11:42:53AM +0200, Thomas Meyer wrote:
> > Am Sonntag, den 20.07.2008, 05:54 +1000 schrieb James Morris:
> > > On Sat, 19 Jul 2008, Rafael J. Wysocki wrote:
> > > 
> > > > > vfs-next/net-next conflict; apply the patch below on top of the
> > > merge.
> > > > 
> > > > That helped, thanks.
> > > > 
> > > > But next it ran into the BUG_ON() in line 883 of
> > > security/selinux/avc.c .
> > > > Disabling selinux made the kernel boot, finally.
> > > 
> > > Ugh, that's not supposed to happen.  Where was this in the boot?  Do
> > > you 
> > > have a console log?
> 
> Argh...  Fallout from ->permission() patch series.  I've folded that into
> rebase (along with Randy's compile fixes and missing bit in capability.c
> in ->inode_permission() patch; AFAICS takes care of all mismerges as well).
> In the meanwhile, see the patch below on top of next-20080718:
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index a15c155..c0a64e2 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -286,7 +286,8 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
>  	if (retval)
>  		return retval;
>  
> -	return security_inode_permission(inode, mask);
> +	return security_inode_permission(inode,
> +					mask & (MAY_READ|MAY_WRITE|MAY_EXEC));
>  }
>  
>  /**

SELinux needs MAY_APPEND to be passed down to the security hook.
Otherwise, we get permission denials when only append permission is
granted by policy even if the opening process specified O_APPEND.
Shows up as a regression in the ltp selinux testsuite, fixed by
this patch.

Signed-off-by:  Stephen Smalley <sds@xxxxxxxxxxxxx>

---

 fs/namei.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index a7b0a0b..b91e973 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -274,7 +274,7 @@ int inode_permission(struct inode *inode, int mask)
 		return retval;
 
 	return security_inode_permission(inode,
-			mask & (MAY_READ|MAY_WRITE|MAY_EXEC));
+			mask & (MAY_READ|MAY_WRITE|MAY_EXEC|MAY_APPEND));
 }
 
 /**


-- 
Stephen Smalley
National Security Agency

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