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Smack: Implement lock security mode

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Linux file locking does not follow the same rules
as other mechanisms. Even though it is a write operation
a process can set a read lock on files which it has open
only for read access. Two programs with read access to
a file can use read locks to communicate.

This is not acceptable in a Mandatory Access Control
environment. Smack treats setting a read lock as the
write operation that it is. Unfortunately, many programs
assume that setting a read lock is a read operation.
These programs are unhappy in the Smack environment.

This patch introduces a new access mode (lock) to address
this problem. A process with lock access to a file can
set a read lock. A process with write access to a file can
set a read lock or a write lock. This prevents a situation
where processes are granted write access just so they can
set read locks.

Targeted for git://git.gitorious.org/smack-next/kernel.git

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
This commit is contained in:
Casey Schaufler 2013-10-11 18:06:39 -07:00
parent 5a5f2acfd0
commit c0ab6e56dc
4 changed files with 33 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
security/smack/smack.h
View file

@ -177,9 +177,13 @@ struct smk_port_label {
#define SMACK_CIPSO_MAXCATNUM 184 /* 23 * 8 */
/*
* Flag for transmute access
* Flags for untraditional access modes.
* It shouldn't be necessary to avoid conflicts with definitions
* in fs.h, but do so anyway.
*/
#define MAY_TRANSMUTE 64
#define MAY_TRANSMUTE 0x00001000 /* Controls directory labeling */
#define MAY_LOCK 0x00002000 /* Locks should be writes, but ... */
/*
* Just to make the common cases easier to deal with
*/
@ -188,9 +192,9 @@ struct smk_port_label {
#define MAY_NOT 0
/*
* Number of access types used by Smack (rwxat)
* Number of access types used by Smack (rwxatl)
*/
#define SMK_NUM_ACCESS_TYPE 5
#define SMK_NUM_ACCESS_TYPE 6
/* SMACK data */
struct smack_audit_data {

10
security/smack/smack_access.c
View file

@ -84,6 +84,8 @@ int log_policy = SMACK_AUDIT_DENIED;
*
* Do the object check first because that is more
* likely to differ.
*
* Allowing write access implies allowing locking.
*/
int smk_access_entry(char *subject_label, char *object_label,
struct list_head *rule_list)
@ -99,6 +101,11 @@ int smk_access_entry(char *subject_label, char *object_label,
}
}
/*
* MAY_WRITE implies MAY_LOCK.
*/
if ((may & MAY_WRITE) == MAY_WRITE)
may |= MAY_LOCK;
return may;
}
@ -245,6 +252,7 @@ int smk_curacc(char *obj_label, u32 mode, struct smk_audit_info *a)
static inline void smack_str_from_perm(char *string, int access)
{
int i = 0;
if (access & MAY_READ)
string[i++] = 'r';
if (access & MAY_WRITE)
@ -255,6 +263,8 @@ static inline void smack_str_from_perm(char *string, int access)
string[i++] = 'a';
if (access & MAY_TRANSMUTE)
string[i++] = 't';
if (access & MAY_LOCK)
string[i++] = 'l';
string[i] = '\0';
}
/**

9
security/smack/smack_lsm.c
View file

@ -1146,7 +1146,7 @@ static int smack_file_ioctl(struct file *file, unsigned int cmd,
* @file: the object
* @cmd: unused
*
* Returns 0 if current has write access, error code otherwise
* Returns 0 if current has lock access, error code otherwise
*/
static int smack_file_lock(struct file *file, unsigned int cmd)
{
@ -1154,7 +1154,7 @@ static int smack_file_lock(struct file *file, unsigned int cmd)
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
smk_ad_setfield_u_fs_path(&ad, file->f_path);
return smk_curacc(file->f_security, MAY_WRITE, &ad);
return smk_curacc(file->f_security, MAY_LOCK, &ad);
}
/**
@ -1178,8 +1178,13 @@ static int smack_file_fcntl(struct file *file, unsigned int cmd,
switch (cmd) {
case F_GETLK:
break;
case F_SETLK:
case F_SETLKW:
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
smk_ad_setfield_u_fs_path(&ad, file->f_path);
rc = smk_curacc(file->f_security, MAY_LOCK, &ad);
break;
case F_SETOWN:
case F_SETSIG:
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);

10
security/smack/smackfs.c
View file

@ -139,7 +139,7 @@ const char *smack_cipso_option = SMACK_CIPSO_OPTION;
* SMK_LOADLEN: Smack rule length
*/
#define SMK_OACCESS "rwxa"
#define SMK_ACCESS "rwxat"
#define SMK_ACCESS "rwxatl"
#define SMK_OACCESSLEN (sizeof(SMK_OACCESS) - 1)
#define SMK_ACCESSLEN (sizeof(SMK_ACCESS) - 1)
#define SMK_OLOADLEN (SMK_LABELLEN + SMK_LABELLEN + SMK_OACCESSLEN)
@ -282,6 +282,10 @@ static int smk_perm_from_str(const char *string)
case 'T':
perm |= MAY_TRANSMUTE;
break;
case 'l':
case 'L':
perm |= MAY_LOCK;
break;
default:
return perm;
}
@ -452,7 +456,7 @@ static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
/*
* Minor hack for backward compatibility
*/
if (count != SMK_OLOADLEN && count != SMK_LOADLEN)
if (count < SMK_OLOADLEN || count > SMK_LOADLEN)
return -EINVAL;
} else {
if (count >= PAGE_SIZE) {
@ -592,6 +596,8 @@ static void smk_rule_show(struct seq_file *s, struct smack_rule *srp, int max)
seq_putc(s, 'a');
if (srp->smk_access & MAY_TRANSMUTE)
seq_putc(s, 't');
if (srp->smk_access & MAY_LOCK)
seq_putc(s, 'l');
seq_putc(s, '\n');
}