From 5cd9c58fbe9ec92b45b27e131719af4f2bd9eb40 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 14 Aug 2008 11:37:28 +0100 Subject: security: Fix setting of PF_SUPERPRIV by __capable() Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags the target process if that is not the current process and it is trying to change its own flags in a different way at the same time. __capable() is using neither atomic ops nor locking to protect t->flags. This patch removes __capable() and introduces has_capability() that doesn't set PF_SUPERPRIV on the process being queried. This patch further splits security_ptrace() in two: (1) security_ptrace_may_access(). This passes judgement on whether one process may access another only (PTRACE_MODE_ATTACH for ptrace() and PTRACE_MODE_READ for /proc), and takes a pointer to the child process. current is the parent. (2) security_ptrace_traceme(). This passes judgement on PTRACE_TRACEME only, and takes only a pointer to the parent process. current is the child. In Smack and commoncap, this uses has_capability() to determine whether the parent will be permitted to use PTRACE_ATTACH if normal checks fail. This does not set PF_SUPERPRIV. Two of the instances of __capable() actually only act on current, and so have been changed to calls to capable(). Of the places that were using __capable(): (1) The OOM killer calls __capable() thrice when weighing the killability of a process. All of these now use has_capability(). (2) cap_ptrace() and smack_ptrace() were using __capable() to check to see whether the parent was allowed to trace any process. As mentioned above, these have been split. For PTRACE_ATTACH and /proc, capable() is now used, and for PTRACE_TRACEME, has_capability() is used. (3) cap_safe_nice() only ever saw current, so now uses capable(). (4) smack_setprocattr() rejected accesses to tasks other than current just after calling __capable(), so the order of these two tests have been switched and capable() is used instead. (5) In smack_file_send_sigiotask(), we need to allow privileged processes to receive SIGIO on files they're manipulating. (6) In smack_task_wait(), we let a process wait for a privileged process, whether or not the process doing the waiting is privileged. I've tested this with the LTP SELinux and syscalls testscripts. Signed-off-by: David Howells Acked-by: Serge Hallyn Acked-by: Casey Schaufler Acked-by: Andrew G. Morgan Acked-by: Al Viro Signed-off-by: James Morris --- security/smack/smack_lsm.c | 49 ++++++++++++++++++++++++++++++++-------------- 1 file changed, 34 insertions(+), 15 deletions(-) (limited to 'security/smack') diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 1b40e558f983..87d75417ea93 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -87,27 +87,46 @@ struct inode_smack *new_inode_smack(char *smack) */ /** - * smack_ptrace - Smack approval on ptrace - * @ptp: parent task pointer + * smack_ptrace_may_access - Smack approval on PTRACE_ATTACH * @ctp: child task pointer * * Returns 0 if access is OK, an error code otherwise * * Do the capability checks, and require read and write. */ -static int smack_ptrace(struct task_struct *ptp, struct task_struct *ctp, - unsigned int mode) +static int smack_ptrace_may_access(struct task_struct *ctp, unsigned int mode) { int rc; - rc = cap_ptrace(ptp, ctp, mode); + rc = cap_ptrace_may_access(ctp, mode); if (rc != 0) return rc; - rc = smk_access(ptp->security, ctp->security, MAY_READWRITE); - if (rc != 0 && __capable(ptp, CAP_MAC_OVERRIDE)) + rc = smk_access(current->security, ctp->security, MAY_READWRITE); + if (rc != 0 && capable(CAP_MAC_OVERRIDE)) return 0; + return rc; +} + +/** + * smack_ptrace_traceme - Smack approval on PTRACE_TRACEME + * @ptp: parent task pointer + * + * Returns 0 if access is OK, an error code otherwise + * + * Do the capability checks, and require read and write. + */ +static int smack_ptrace_traceme(struct task_struct *ptp) +{ + int rc; + + rc = cap_ptrace_traceme(ptp); + if (rc != 0) + return rc; + rc = smk_access(ptp->security, current->security, MAY_READWRITE); + if (rc != 0 && has_capability(ptp, CAP_MAC_OVERRIDE)) + return 0; return rc; } @@ -923,7 +942,7 @@ static int smack_file_send_sigiotask(struct task_struct *tsk, */ file = container_of(fown, struct file, f_owner); rc = smk_access(file->f_security, tsk->security, MAY_WRITE); - if (rc != 0 && __capable(tsk, CAP_MAC_OVERRIDE)) + if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE)) return 0; return rc; } @@ -1164,12 +1183,12 @@ static int smack_task_wait(struct task_struct *p) * account for the smack labels having gotten to * be different in the first place. * - * This breaks the strict subjet/object access + * This breaks the strict subject/object access * control ideal, taking the object's privilege * state into account in the decision as well as * the smack value. */ - if (capable(CAP_MAC_OVERRIDE) || __capable(p, CAP_MAC_OVERRIDE)) + if (capable(CAP_MAC_OVERRIDE) || has_capability(p, CAP_MAC_OVERRIDE)) return 0; return rc; @@ -2016,9 +2035,6 @@ static int smack_setprocattr(struct task_struct *p, char *name, { char *newsmack; - if (!__capable(p, CAP_MAC_ADMIN)) - return -EPERM; - /* * Changing another process' Smack value is too dangerous * and supports no sane use case. @@ -2026,6 +2042,9 @@ static int smack_setprocattr(struct task_struct *p, char *name, if (p != current) return -EPERM; + if (!capable(CAP_MAC_ADMIN)) + return -EPERM; + if (value == NULL || size == 0 || size >= SMK_LABELLEN) return -EINVAL; @@ -2552,7 +2571,8 @@ static void smack_release_secctx(char *secdata, u32 seclen) struct security_operations smack_ops = { .name = "smack", - .ptrace = smack_ptrace, + .ptrace_may_access = smack_ptrace_may_access, + .ptrace_traceme = smack_ptrace_traceme, .capget = cap_capget, .capset_check = cap_capset_check, .capset_set = cap_capset_set, @@ -2729,4 +2749,3 @@ static __init int smack_init(void) * all processes and objects when they are created. */ security_initcall(smack_init); - -- cgit v1.2.2