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security: make inode_follow_link RCU-walk aware

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inode_follow_link now takes an inode and rcu flag as well as the
dentry.

inode is used in preference to d_backing_inode(dentry), particularly
in RCU-walk mode.

selinux_inode_follow_link() gets dentry_has_perm() and
inode_has_perm() open-coded into it so that it can call
avc_has_perm_flags() in way that is safe if LOOKUP_RCU is set.

Calling avc_has_perm_flags() with rcu_read_lock() held means
that when avc_has_perm_noaudit calls avc_compute_av(), the attempt
to rcu_read_unlock() before calling security_compute_av() will not
actually drop the RCU read-lock.

However as security_compute_av() is completely in a read_lock()ed
region, it should be safe with the RCU read-lock held.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
NeilBrown
2015-03-23 13:37:39 +11:00
committed by Al Viro
parent 7b20ea2579
commit bda0be7ad9
5 changed files with 32 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
security/capability.c
+2 -1
View File
@@ -209,7 +209,8 @@ static int cap_inode_readlink(struct dentry *dentry)
return 0;
}
static int cap_inode_follow_link(struct dentry *dentry)
static int cap_inode_follow_link(struct dentry *dentry, struct inode *inode,
bool rcu)
{
return 0;
}
security/security.c
+4 -3
View File
@@ -581,11 +581,12 @@ int security_inode_readlink(struct dentry *dentry)
return security_ops->inode_readlink(dentry);
}
int security_inode_follow_link(struct dentry *dentry)
int security_inode_follow_link(struct dentry *dentry, struct inode *inode,
bool rcu)
{
if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
if (unlikely(IS_PRIVATE(inode)))
return 0;
return security_ops->inode_follow_link(dentry);
return security_ops->inode_follow_link(dentry, inode, rcu);
}
int security_inode_permission(struct inode *inode, int mask)
security/selinux/hooks.c
+14 -2
View File
@@ -2861,11 +2861,23 @@ static int selinux_inode_readlink(struct dentry *dentry)
return dentry_has_perm(cred, dentry, FILE__READ);
}
static int selinux_inode_follow_link(struct dentry *dentry)
static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
bool rcu)
{
const struct cred *cred = current_cred();
struct common_audit_data ad;
struct inode_security_struct *isec;
u32 sid;
return dentry_has_perm(cred, dentry, FILE__READ);
validate_creds(cred);
ad.type = LSM_AUDIT_DATA_DENTRY;
ad.u.dentry = dentry;
sid = cred_sid(cred);
isec = inode->i_security;
return avc_has_perm_flags(sid, isec->sid, isec->sclass, FILE__READ, &ad,
rcu ? MAY_NOT_BLOCK : 0);
}
static noinline int audit_inode_permission(struct inode *inode,