[PATCH AUTOSEL for 4.4 065/167] selinux: do not check open permission on sockets

Sasha Levin
2018-03-19T16:09:08Z

From: Stephen Smalley <sds@tycho.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@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.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 3f370eb494d1..d41dd75c1804 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1958,8 +1958,9 @@ 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;
@@ -2928,6 +2929,7 @@ 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;

@@ -2943,8 +2945,10 @@ 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