From c0ab6e56dcb7ca9903d460247cb464e769ae6e77 Mon Sep 17 00:00:00 2001 From: Casey Schaufler Date: Fri, 11 Oct 2013 18:06:39 -0700 Subject: [PATCH] Smack: Implement lock security mode 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 --- security/smack/smack.h | 12 ++++++++---- security/smack/smack_access.c | 10 ++++++++++ security/smack/smack_lsm.c | 9 +++++++-- security/smack/smackfs.c | 10 ++++++++-- 4 files changed, 33 insertions(+), 8 deletions(-) diff --git a/security/smack/smack.h b/security/smack/smack.h index 076b8e8a51ab..364cc64fce71 100644 --- a/security/smack/smack.h +++ b/security/smack/smack.h @@ -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 { diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c index b3b59b1e93d6..14293cd9b1e5 100644 --- a/security/smack/smack_access.c +++ b/security/smack/smack_access.c @@ -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 @@ out_audit: 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'; } /** diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 8825375cc031..88d366e55793 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -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); diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c index 80f4b4a45725..160aa08e3cd5 100644 --- a/security/smack/smackfs.c +++ b/security/smack/smackfs.c @@ -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'); } -- 2.39.5