Messages in this thread Patch in this message | | | Date | Wed, 21 Apr 2004 12:37:30 -0700 | From | Andy Lutomirski <> | Subject | Re: compute_creds fixup in -mm |
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Stephen Smalley wrote:
> On Wed, 2004-04-21 at 14:28, Chris Wright wrote: > >>* Stephen Smalley (sds@epoch.ncsc.mil) wrote: >> >>>I didn't see Chris' patch. I assume that the worst case is unexpected >>>program failure due to lack of capability, right? The SELinux security >> >>The opposite. You'd get a program with non-root euid, but full >>capability set, and AT_SECURE set false. My patch is below. > > > Sorry, I wasn't clear. I meant the worst case due to the share/ptrace > state check being duplicated in SELinux and in commoncap, as opposed to > being performed once as in Andy's patch. >
I was worried about sid changing but uid and caps staying the same if a ptrace_detach or _exit happens between the cap_bprm_apply_creds call and the rest of selinux_bprm_apply_creds. Remember the sendmail bug -- program failure due to lack of capabilities can cause privilege leaks (in this case selinux sid leaks).
If this isn't a concern, then Chris' patch should be fine. On the other hand, some other LSM may prefer my version. Here's my corrected patch (thanks, Chris):
--- linux-2.6.5-mm5/include/linux/security.h.ptlock 2004-04-21 08:52:49.904877920 -0700 +++ linux-2.6.5-mm5/include/linux/security.h 2004-04-21 09:12:46.540961584 -0700 @@ -44,7 +44,7 @@ extern int cap_capset_check (struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); extern void cap_capset_set (struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); extern int cap_bprm_set_security (struct linux_binprm *bprm); -extern void cap_bprm_apply_creds (struct linux_binprm *bprm); +extern void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe); extern int cap_bprm_secureexec(struct linux_binprm *bprm); extern int cap_inode_setxattr(struct dentry *dentry, char *name, void *value, size_t size, int flags); extern int cap_inode_removexattr(struct dentry *dentry, char *name); @@ -86,6 +86,11 @@ struct sched_param; struct swap_info_struct;
+/* brpm_apply_creds unsafe reasons */ +#define LSM_UNSAFE_SHARE 1 +#define LSM_UNSAFE_PTRACE 2 +#define LSM_UNSAFE_PTRACE_CAP 4 + #ifdef CONFIG_SECURITY
/** @@ -112,6 +117,8 @@ * also perform other state changes on the process (e.g. closing open * file descriptors to which access is no longer granted if the attributes * were changed). + * bprm_apply_creds is called under task_lock. @unsafe indicates various + * reasons why it may be unsafe to change security state. * @bprm contains the linux_binprm structure. * @bprm_set_security: * Save security information in the bprm->security field, typically based @@ -1026,7 +1033,7 @@
int (*bprm_alloc_security) (struct linux_binprm * bprm); void (*bprm_free_security) (struct linux_binprm * bprm); - void (*bprm_apply_creds) (struct linux_binprm * bprm); + void (*bprm_apply_creds) (struct linux_binprm * bprm, int unsafe); int (*bprm_set_security) (struct linux_binprm * bprm); int (*bprm_check_security) (struct linux_binprm * bprm); int (*bprm_secureexec) (struct linux_binprm * bprm); @@ -1290,9 +1297,9 @@ { security_ops->bprm_free_security (bprm); } -static inline void security_bprm_apply_creds (struct linux_binprm *bprm) +static inline void security_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) { - security_ops->bprm_apply_creds (bprm); + security_ops->bprm_apply_creds (bprm, unsafe); } static inline int security_bprm_set (struct linux_binprm *bprm) { @@ -1962,9 +1969,9 @@ static inline void security_bprm_free (struct linux_binprm *bprm) { }
-static inline void security_bprm_apply_creds (struct linux_binprm *bprm) +static inline void security_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) { - cap_bprm_apply_creds (bprm); + cap_bprm_apply_creds (bprm, unsafe); }
static inline int security_bprm_set (struct linux_binprm *bprm) --- linux-2.6.5-mm5/fs/exec.c.ptlock 2004-04-21 08:50:37.767965784 -0700 +++ linux-2.6.5-mm5/fs/exec.c 2004-04-21 12:23:01.915761696 -0700 @@ -919,24 +919,28 @@
EXPORT_SYMBOL(prepare_binprm);
-/* - * This function is used to produce the new IDs and capabilities - * from the old ones and the file's capabilities. - * - * The formula used for evolving capabilities is: - * - * pI' = pI - * (***) pP' = (fP & X) | (fI & pI) - * pE' = pP' & fE [NB. fE is 0 or ~0] - * - * I=Inheritable, P=Permitted, E=Effective // p=process, f=file - * ' indicates post-exec(), and X is the global 'cap_bset'. - * - */ +static inline int must_not_trace_exec (struct task_struct *p) +{ + int unsafe = 0; + if (p->ptrace & PT_PTRACED) { + if(p->ptrace & PT_PTRACE_CAP) + unsafe |= LSM_UNSAFE_PTRACE_CAP; + else + unsafe |= LSM_UNSAFE_PTRACE; + } + if (atomic_read(&p->fs->count) > 1 || + atomic_read(&p->files->count) > 1 || + atomic_read(&p->sighand->count) > 1) + unsafe |= LSM_UNSAFE_SHARE; + + return unsafe; +}
void compute_creds(struct linux_binprm *bprm) { - security_bprm_apply_creds(bprm); + task_lock(current); + security_bprm_apply_creds(bprm, must_not_trace_exec(current)); + task_unlock(current); }
EXPORT_SYMBOL(compute_creds); --- linux-2.6.5-mm5/security/selinux/hooks.c.ptlock 2004-04-21 08:57:16.947281304 -0700 +++ linux-2.6.5-mm5/security/selinux/hooks.c 2004-04-21 12:23:58.245198320 -0700 @@ -1746,7 +1746,7 @@ spin_unlock(&files->file_lock); }
-static void selinux_bprm_apply_creds(struct linux_binprm *bprm) +static void selinux_bprm_apply_creds(struct linux_binprm *bprm, int unsafe) { struct task_security_struct *tsec, *psec; struct bprm_security_struct *bsec; @@ -1756,7 +1756,7 @@ struct rlimit *rlim, *initrlim; int rc, i;
- secondary_ops->bprm_apply_creds(bprm); + secondary_ops->bprm_apply_creds(bprm, unsafe);
tsec = current->security;
@@ -1767,9 +1767,7 @@ if (tsec->sid != sid) { /* Check for shared state. If not ok, leave SID unchanged and kill. */ - if ((atomic_read(¤t->fs->count) > 1 || - atomic_read(¤t->files->count) > 1 || - atomic_read(¤t->sighand->count) > 1)) { + if (unsafe & LSM_UNSAFE_SHARE) { rc = avc_has_perm(tsec->sid, sid, SECCLASS_PROCESS, PROCESS__SHARE, NULL, NULL); @@ -1781,15 +1779,13 @@
/* Check for ptracing, and update the task SID if ok. Otherwise, leave SID unchanged and kill. */ - task_lock(current); - if (current->ptrace & PT_PTRACED) { + if (unsafe & (LSM_UNSAFE_PTRACE | LSM_UNSAFE_PTRACE_CAP)) { psec = current->parent->security; rc = avc_has_perm_noaudit(psec->sid, sid, SECCLASS_PROCESS, PROCESS__PTRACE, NULL, &avd); if (!rc) tsec->sid = sid; - task_unlock(current); avc_audit(psec->sid, sid, SECCLASS_PROCESS, PROCESS__PTRACE, &avd, rc, NULL); if (rc) { @@ -1798,7 +1794,6 @@ } } else { tsec->sid = sid; - task_unlock(current); }
/* Close files for which the new task SID is not authorized. */ --- linux-2.6.5-mm5/security/commoncap.c.ptlock 2004-04-21 08:54:16.824664104 -0700 +++ linux-2.6.5-mm5/security/commoncap.c 2004-04-21 09:24:01.468357024 -0700 @@ -115,15 +115,7 @@ return 0; }
-static inline int must_not_trace_exec (struct task_struct *p) -{ - return ((p->ptrace & PT_PTRACED) && !(p->ptrace & PT_PTRACE_CAP)) - || atomic_read(&p->fs->count) > 1 - || atomic_read(&p->files->count) > 1 - || atomic_read(&p->sighand->count) > 1; -} - -void cap_bprm_apply_creds (struct linux_binprm *bprm) +void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) { /* Derived from fs/exec.c:compute_creds. */ kernel_cap_t new_permitted, working; @@ -133,30 +125,25 @@ current->cap_inheritable); new_permitted = cap_combine (new_permitted, working);
- task_lock(current); - - if (bprm->e_uid != current->uid || bprm->e_gid != current->gid) { + if (bprm->e_uid != current->uid || bprm->e_gid != current->gid || + !cap_issubset (new_permitted, current->cap_permitted)) { current->mm->dumpable = 0;
- if (must_not_trace_exec(current) && !capable(CAP_SETUID)) { - bprm->e_uid = current->uid; - bprm->e_gid = current->gid; + if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) { + if (!capable(CAP_SETUID)) { + bprm->e_uid = current->uid; + bprm->e_gid = current->gid; + } + if (!capable (CAP_SETPCAP)) { + new_permitted = cap_intersect (new_permitted, + current->cap_permitted); + } } }
current->suid = current->euid = current->fsuid = bprm->e_uid; current->sgid = current->egid = current->fsgid = bprm->e_gid;
- if (!cap_issubset (new_permitted, current->cap_permitted)) { - current->mm->dumpable = 0; - - if (must_not_trace_exec (current) && !capable (CAP_SETPCAP)) { - new_permitted = cap_intersect (new_permitted, - current-> - cap_permitted); - } - } - /* For init, we want to retain the capabilities set * in the init_task struct. Thus we skip the usual * capability rules */ @@ -167,7 +154,6 @@ }
/* AUD: Audit candidate if current->cap_effective is set */ - task_unlock(current);
current->keep_capabilities = 0; } --- linux-2.6.5-mm5/security/dummy.c.ptlock 2004-04-21 08:56:00.608886504 -0700 +++ linux-2.6.5-mm5/security/dummy.c 2004-04-21 09:14:57.345076336 -0700 @@ -171,21 +171,12 @@ return; }
-static inline int must_not_trace_exec (struct task_struct *p) +static void dummy_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) { - return ((p->ptrace & PT_PTRACED) && !(p->ptrace & PT_PTRACE_CAP)) - || atomic_read(&p->fs->count) > 1 - || atomic_read(&p->files->count) > 1 - || atomic_read(&p->sighand->count) > 1; -} - -static void dummy_bprm_apply_creds (struct linux_binprm *bprm) -{ - task_lock(current); if (bprm->e_uid != current->uid || bprm->e_gid != current->gid) { current->mm->dumpable = 0;
- if (must_not_trace_exec(current) && !capable(CAP_SETUID)) { + if (unsafe && !capable(CAP_SETUID)) { bprm->e_uid = current->uid; bprm->e_gid = current->gid; } @@ -193,8 +184,6 @@
current->suid = current->euid = current->fsuid = bprm->e_uid; current->sgid = current->egid = current->fsgid = bprm->e_gid; - - task_unlock(current); }
static int dummy_bprm_set_security (struct linux_binprm *bprm) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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