selinux: do not check open permission on sockets

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@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e29800091e17..627f291fb6c1 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2063,8 +2063,9 @@ 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;
@@ -3059,6 +3060,7 @@ 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;
 
@@ -3074,8 +3076,10 @@ 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);