From: Davidlohr Bueso <dave@xxxxxxxxxxxx> Subject: ipc/sem: introduce semctl(SEM_STAT_ANY) There is a permission discrepancy when consulting shm ipc object metadata between /proc/sysvipc/sem (0444) and the SEM_STAT semctl command. The later does permission checks for the object vs S_IRUGO. As such there can be cases where EACCESS is returned via syscall but the info is displayed anyways in the procfs files. While this might have security implications via info leaking (albeit no writing to the sma metadata), this behavior goes way back and showing all the objects regardless of the permissions was most likely an overlook - so we are stuck with it. Furthermore, modifying either the syscall or the procfs file can cause userspace programs to break (ie ipcs). Some applications require getting the procfs info (without root privileges) and can be rather slow in comparison with a syscall -- up to 500x in some reported cases for shm. This patch introduces a new SEM_STAT_ANY command such that the sem ipc object permissions are ignored, and only audited instead. In addition, I've left the lsm security hook checks in place, as if some policy can block the call, then the user has no other choice than just parsing the procfs file. Link: http://lkml.kernel.org/r/20180215162458.10059-3-dave@xxxxxxxxxxxx Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> Reported-by: Robert Kettler <robert.kettler@xxxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/uapi/linux/sem.h | 1 + ipc/sem.c | 17 ++++++++++++----- security/selinux/hooks.c | 1 + security/smack/smack_lsm.c | 1 + 4 files changed, 15 insertions(+), 5 deletions(-) diff -puN include/uapi/linux/sem.h~ipc-sem-introduce-semctlsem_stat_any include/uapi/linux/sem.h --- a/include/uapi/linux/sem.h~ipc-sem-introduce-semctlsem_stat_any +++ a/include/uapi/linux/sem.h @@ -19,6 +19,7 @@ /* ipcs ctl cmds */ #define SEM_STAT 18 #define SEM_INFO 19 +#define SEM_STAT_ANY 20 /* Obsolete, used only for backwards compatibility and libc5 compiles */ struct semid_ds { diff -puN ipc/sem.c~ipc-sem-introduce-semctlsem_stat_any ipc/sem.c --- a/ipc/sem.c~ipc-sem-introduce-semctlsem_stat_any +++ a/ipc/sem.c @@ -1220,14 +1220,14 @@ static int semctl_stat(struct ipc_namesp memset(semid64, 0, sizeof(*semid64)); rcu_read_lock(); - if (cmd == SEM_STAT) { + if (cmd == SEM_STAT || cmd == SEM_STAT_ANY) { sma = sem_obtain_object(ns, semid); if (IS_ERR(sma)) { err = PTR_ERR(sma); goto out_unlock; } id = sma->sem_perm.id; - } else { + } else { /* IPC_STAT */ sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { err = PTR_ERR(sma); @@ -1235,9 +1235,14 @@ static int semctl_stat(struct ipc_namesp } } - err = -EACCES; - if (ipcperms(ns, &sma->sem_perm, S_IRUGO)) - goto out_unlock; + /* see comment for SHM_STAT_ANY */ + if (cmd == SEM_STAT_ANY) + audit_ipc_obj(&sma->sem_perm); + else { + err = -EACCES; + if (ipcperms(ns, &sma->sem_perm, S_IRUGO)) + goto out_unlock; + } err = security_sem_semctl(&sma->sem_perm, cmd); if (err) @@ -1626,6 +1631,7 @@ long ksys_semctl(int semid, int semnum, return semctl_info(ns, semid, cmd, p); case IPC_STAT: case SEM_STAT: + case SEM_STAT_ANY: err = semctl_stat(ns, semid, cmd, &semid64); if (err < 0) return err; @@ -1732,6 +1738,7 @@ long compat_ksys_semctl(int semid, int s return semctl_info(ns, semid, cmd, p); case IPC_STAT: case SEM_STAT: + case SEM_STAT_ANY: err = semctl_stat(ns, semid, cmd, &semid64); if (err < 0) return err; diff -puN security/selinux/hooks.c~ipc-sem-introduce-semctlsem_stat_any security/selinux/hooks.c --- a/security/selinux/hooks.c~ipc-sem-introduce-semctlsem_stat_any +++ a/security/selinux/hooks.c @@ -6273,6 +6273,7 @@ static int selinux_sem_semctl(struct ker break; case IPC_STAT: case SEM_STAT: + case SEM_STAT_ANY: perms = SEM__GETATTR | SEM__ASSOCIATE; break; default: diff -puN security/smack/smack_lsm.c~ipc-sem-introduce-semctlsem_stat_any security/smack/smack_lsm.c --- a/security/smack/smack_lsm.c~ipc-sem-introduce-semctlsem_stat_any +++ a/security/smack/smack_lsm.c @@ -3140,6 +3140,7 @@ static int smack_sem_semctl(struct kern_ case GETALL: case IPC_STAT: case SEM_STAT: + case SEM_STAT_ANY: may = MAY_READ; break; case SETVAL: _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
