net: Update the sysctl permissions handler to test effective uid/gid

PATCH In review Eric W. Biederman 2 participants 2 messages Oct 5, 2013 – Oct 7, 2013 7 messages not in the archive

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Eric W. Biederman

author

2013-10-05 20:15 UTC #7 lore raw

PATCH 1/1 net: Update the sysctl permissions handler to test effective uid/gid

Quoted 23 lines · On Tue, 20 Aug 2013 11:40:04 -0500 Eric Sandeen <[email protected]> wrote:

This was brought up in a Red Hat bug (which may be marked private, I'm sorry):
Bug 987055 - open O_WRONLY succeeds on some root owned files in /proc for process running with unprivileged EUID
"On RHEL7 some of the files in /proc can be opened for writing by an unprivileged EUID."
The flaw existed upstream as well last I checked.
This commit in kernel v3.8 caused the regression:
commit cff109768b2d9c03095848f4cd4b0754117262aa
Author: Eric W. Biederman <[email protected]>
Date:   Fri Nov 16 03:03:01 2012 +0000
net: Update the per network namespace sysctls to be available to the network namespace owner
- Allow anyone with CAP_NET_ADMIN rights in the user namespace of the the netowrk namespace to change sysctls.
- Allow anyone the uid of the user namespace root the same permissions over the network namespace sysctls as the global root.
- Allow anyone with gid of the user namespace root group the same permissions over the network namespace sysctl as the global root group.

Quoted 8 lines

Signed-off-by "Eric W. Biederman" <[email protected]>
Signed-off-by David S. Miller <[email protected]>
because it changed /sys/net's special permission handler to test current_uid, not current_euid; same for current_gid/current_egid.
So in this case, root cannot drop privs via set[ug]id, and retains all privs in this codepath.

Modify the code to use current_euid(), and in_egroup_p, as in done in fs/proc/proc_sysctl.c:test_perm()

Cc [email protected]

Reviewed-by Eric Sandeen <[email protected]>

Reported-by Eric Sandeen <[email protected]>

Signed-off-by "Eric W. Biederman" <[email protected]>

---

Resubmitting as it looks like this fix got lost. This patch applies cleanly against both net-next and linux-3.12-rc1, and likely quite a few early kernel revisions.

 net/sysctl_net.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

net/sysctl_net.c +2 -2

index 9bc6db04be3e..e7000be321b0 100644
@@ -47,12 +47,12 @@ static int net_ctl_permissions(struct ctl_table_header *head,
 
 	/* Allow network administrator to have same access as root. */
 	if (ns_capable(net->user_ns, CAP_NET_ADMIN) ||
-	    uid_eq(root_uid, current_uid())) {
+	    uid_eq(root_uid, current_euid())) {
 		int mode = (table->mode >> 6) & 7;
 		return (mode << 6) | (mode << 3) | mode;
 	}
 	/* Allow netns root group to have the same access as the root group */
-	if (gid_eq(root_gid, current_gid())) {
+	if (in_egroup_p(root_gid)) {
 		int mode = (table->mode >> 3) & 7;
 		return (mode << 3) | mode;
 	}

Signature · 1 line

1.7.5.4

David Miller

maintainer

2013-10-07 19:58 UTC #8 lore raw

From: [email protected] (Eric W. Biederman)
Date: Sat, 05 Oct 2013 13:15:30 -0700

Quoted 34 lines · On Tue, 20 Aug 2013 11:40:04 -0500 Eric Sandeen <[email protected]> wrote:

Quoted 23 lines
This was brought up in a Red Hat bug (which may be marked private, I'm sorry):
Bug 987055 - open O_WRONLY succeeds on some root owned files in /proc for process running with unprivileged EUID
"On RHEL7 some of the files in /proc can be opened for writing by an unprivileged EUID."
The flaw existed upstream as well last I checked.
This commit in kernel v3.8 caused the regression:
commit cff109768b2d9c03095848f4cd4b0754117262aa
Author: Eric W. Biederman <[email protected]>
Date:   Fri Nov 16 03:03:01 2012 +0000
net: Update the per network namespace sysctls to be available to the network namespace owner
- Allow anyone with CAP_NET_ADMIN rights in the user namespace of the the netowrk namespace to change sysctls.
- Allow anyone the uid of the user namespace root the same permissions over the network namespace sysctls as the global root.
- Allow anyone with gid of the user namespace root group the same permissions over the network namespace sysctl as the global root group.
Quoted 8 lines
Signed-off-by "Eric W. Biederman" <[email protected]>
Signed-off-by David S. Miller <[email protected]>
because it changed /sys/net's special permission handler to test current_uid, not current_euid; same for current_gid/current_egid.
So in this case, root cannot drop privs via set[ug]id, and retains all privs in this codepath.

Quoted 7 lines

Modify the code to use current_euid(), and in_egroup_p, as in done in fs/proc/proc_sysctl.c:test_perm()
Cc [email protected]
Reviewed-by Eric Sandeen <[email protected]>
Reported-by Eric Sandeen <[email protected]>
Signed-off-by "Eric W. Biederman" <[email protected]>

Applied and queued up for -stable, thanks.