linux-kernel - [PATCH AUTOSEL for 4.9 097/281] selinux: do not check open permission on sockets

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Message-ID: <20180319155742.13731-97-alexander.levin@microsoft.com>
Date:   Mon, 19 Mar 2018 15:59:47 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Stephen Smalley <sds@...ho.nsa.gov>,
        Paul Moore <paul@...l-moore.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.9 097/281] selinux: do not check open permission
 on sockets

From: Stephen Smalley <sds@...ho.nsa.gov>

[ Upstream commit ccb544781d34afdb73a9a73ae53035d824d193bf ]

open permission is currently only defined for files in the kernel
(COMMON_FILE_PERMS rather than COMMON_FILE_SOCK_PERMS). Construction of
an artificial test case that tries to open a socket via /proc/pid/fd will
generate a recvfrom avc denial because recvfrom and open happen to map to
the same permission bit in socket vs file classes.

open of a socket via /proc/pid/fd is not supported by the kernel regardless
and will ultimately return ENXIO. But we hit the permission check first and
can thus produce these odd/misleading denials.  Omit the open check when
operating on a socket.

Signed-off-by: Stephen Smalley <sds@...ho.nsa.gov>
Signed-off-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 security/selinux/hooks.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c2da45ae5b2a..a3d2db613974 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2049,8 +2049,9 @@ static inline u32 file_to_av(struct file *file)
 static inline u32 open_file_to_av(struct file *file)
 {
 	u32 av = file_to_av(file);
+	struct inode *inode = file_inode(file);
 
-	if (selinux_policycap_openperm)
+	if (selinux_policycap_openperm && inode->i_sb->s_magic != SOCKFS_MAGIC)
 		av |= FILE__OPEN;
 
 	return av;
@@ -3047,6 +3048,7 @@ static int selinux_inode_permission(struct inode *inode, int mask)
 static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	const struct cred *cred = current_cred();
+	struct inode *inode = d_backing_inode(dentry);
 	unsigned int ia_valid = iattr->ia_valid;
 	__u32 av = FILE__WRITE;
 
@@ -3062,8 +3064,10 @@ static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
 			ATTR_ATIME_SET | ATTR_MTIME_SET | ATTR_TIMES_SET))
 		return dentry_has_perm(cred, dentry, FILE__SETATTR);
 
-	if (selinux_policycap_openperm && (ia_valid & ATTR_SIZE)
-			&& !(ia_valid & ATTR_FILE))
+	if (selinux_policycap_openperm &&
+	    inode->i_sb->s_magic != SOCKFS_MAGIC &&
+	    (ia_valid & ATTR_SIZE) &&
+	    !(ia_valid & ATTR_FILE))
 		av |= FILE__OPEN;
 
 	return dentry_has_perm(cred, dentry, av);
-- 
2.14.1