4.18-rc1 regression in /proc/self xattr handling

4.18-rc1 regression in /proc/self xattr handling

[Casey Schaufler]

There is a regression in behavior regarding xattrs in /proc after:

commit 1bbc55131e59bd099fdc568d3aa0b42634dbd188
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Wed May 2 21:26:16 2018 -0400

    procfs: get rid of ancient BS in pid_revalidate() uses
    

Prior to this change lgetxattr() would provide the correct attributes
for entries in /proc. With this change I see that while the behavior
remains correct if the procid is specified, it is not when "self" is
used. On a system with Smack enabled, where the shell has the Smack label
"Crackle" I see: 

[root at localhost linux]# attr -S -g SMACK64 /proc/self/attr/current
Attribute "SMACK64" had a 1 byte value for /proc/self/attr/current:
_
[root at localhost linux]# attr -S -g SMACK64 /proc/$BASHPID/attr/current
Attribute "SMACK64" had a 7 byte value for /proc/1716/attr/current:
Crackle

These should be the same, and in the past have been. I don't know
what SELinux expects as far as attributes in /proc, so I can't say
if the problem is manifest with SELinux.


--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

4.18-rc1 regression in /proc/self xattr handling

[Al Viro]

On Fri, Jun 22, 2018 at 07:37:00AM -0700, Casey Schaufler wrote:
> There is a regression in behavior regarding xattrs in /proc after:
> 
> commit 1bbc55131e59bd099fdc568d3aa0b42634dbd188
> Author: Al Viro <viro@zeniv.linux.org.uk>
> Date:   Wed May 2 21:26:16 2018 -0400
> 
>     procfs: get rid of ancient BS in pid_revalidate() uses
>     
> 
> Prior to this change lgetxattr() would provide the correct attributes
> for entries in /proc. With this change I see that while the behavior
> remains correct if the procid is specified, it is not when "self" is
> used. On a system with Smack enabled, where the shell has the Smack label
> "Crackle" I see: 
> 
> [root at localhost linux]# attr -S -g SMACK64 /proc/self/attr/current
> Attribute "SMACK64" had a 1 byte value for /proc/self/attr/current:
> _
> [root at localhost linux]# attr -S -g SMACK64 /proc/$BASHPID/attr/current
> Attribute "SMACK64" had a 7 byte value for /proc/1716/attr/current:
> Crackle

Wait a sec - the former will be that of attr, the latter - of bash;
it's not the same file at all.

> These should be the same, and in the past have been. I don't know
> what SELinux expects as far as attributes in /proc, so I can't say
> if the problem is manifest with SELinux.

Very interesting...  About the only thing changed here seems to be
the relative order of smack_d_instantiate() and smack_task_to_inode()...

Would setting SMK_INODE_INSTANT in isp->smk_flags in smack_task_to_inode()
be the right thing to do, anyway?
--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH] Smack: Mark inode instant in smack_task_to_inode

[Casey Schaufler]

Smack: Mark inode instant in smack_task_to_inode

/proc clean-up in commit 1bbc55131e59bd099fdc568d3aa0b42634dbd188
resulted in smack_task_to_inode() being called before smack_d_instantiate.
This resulted in the smk_inode value being ignored, even while present
for files in /proc/self. Marking the inode as instant here fixes that.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 security/smack/smack_lsm.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 7ad226018f51..19de675d4504 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2296,6 +2296,7 @@ static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
 	struct smack_known *skp = smk_of_task_struct(p);
 
 	isp->smk_inode = skp;
+	isp->smk_flags |= SMK_INODE_INSTANT;
 }
 
 /*

--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html