Re: [PATCH -v3 4/5] AUDIT: collect info when execve results in caps in pE

Serge E. Hallyn
2008-11-10T14:53:34Z

Quoting Eric Paris (eparis@redhat.com):
> Any time fcaps or a setuid app under SECURE_NOROOT is used to result in a
> non-zero pE we will crate a new audit record which contains the entire set
> of known information about the executable in question, fP, fI, fE, fversion
> and includes the process's pE, pI, pP. Before and after the bprm capability
> are applied. This record type will only be emitted from execve syscalls.
>
> an example of making ping use fcaps instead of setuid:
>
> setcap "cat_net_raw+pe" /bin/ping
>
> type=SYSCALL msg=audit(1225742021.015:236): arch=c000003e syscall=59 success=yes exit=0 a0=1457f30 a1=14606b0 a2=1463940 a3=321b770a70 items=2 ppid=2929 pid=2963 auid=0 uid=500 gid=500 euid=500 suid=500 fsuid=500 egid=500 sgid=500 fsgid=500 tty=pts0 ses=3 comm="ping" exe="/bin/ping" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null)
> type=UNKNOWN[1321] msg=audit(1225742021.015:236): fver=2 fp=0000000000002000 fi=0000000000000000 fe=1 old_pp=0000000000000000 old_pi=0000000000000000 old_pe=0000000000000000 new_pp=0000000000002000 new_pi=0000000000000000 new_pe=0000000000002000
> type=EXECVE msg=audit(1225742021.015:236): argc=2 a0="ping" a1="127.0.0.1"
> type=CWD msg=audit(1225742021.015:236): cwd="/home/test"
> type=PATH msg=audit(1225742021.015:236): item=0 name="/bin/ping" inode=49256 dev=fd:00 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ping_exec_t:s0 cap_fp=0000000000002000 cap_fe=1 cap_fver=2
> type=PATH msg=audit(1225742021.015:236): item=1 name=(null) inode=507915 dev=fd:00 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ld_so_t:s0
>
> Signed-off-by: Eric Paris <eparis@redhat.com>

Acked-by: Serge Hallyn <serue@us.ibm.com>

thanks

-serge

> ---
>
> include/linux/audit.h | 26 +++++++++++++++++++
> kernel/auditsc.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
> security/commoncap.c | 23 ++++++++++++++++-
> 3 files changed, 116 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 6272a39..8cfb9fe 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -99,6 +99,7 @@
> #define AUDIT_OBJ_PID 1318 /* ptrace target */
> #define AUDIT_TTY 1319 /* Input on an administrative TTY */
> #define AUDIT_EOE 1320 /* End of multi-record event */
> +#define AUDIT_BPRM_FCAPS 1321 /* Information about fcaps increasing perms */
>
> #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> @@ -452,6 +453,7 @@ extern int __audit_mq_timedsend(mqd_t mqdes, size_t msg_len, unsigned int msg_pr
> extern int __audit_mq_timedreceive(mqd_t mqdes, size_t msg_len, unsigned int __user *u_msg_prio, const struct timespec __user *u_abs_timeout);
> extern int __audit_mq_notify(mqd_t mqdes, const struct sigevent __user *u_notification);
> extern int __audit_mq_getsetattr(mqd_t mqdes, struct mq_attr *mqstat);
> +extern void __audit_log_bprm_fcaps(struct linux_binprm *bprm, kernel_cap_t *pP, kernel_cap_t *pE);
>
> static inline int audit_ipc_obj(struct kern_ipc_perm *ipcp)
> {
> @@ -501,6 +503,29 @@ static inline int audit_mq_getsetattr(mqd_t mqdes, struct mq_attr *mqstat)
> return __audit_mq_getsetattr(mqdes, mqstat);
> return 0;
> }
> +
> +/*
> + * ieieeeeee, an audit function without a return code!
> + *
> + * This function might fail! I decided that it didn't matter. We are too late
> + * to fail the syscall and the information isn't REQUIRED for any purpose. It's
> + * just nice to have. We should be able to look at past audit logs to figure
> + * out this process's current cap set along with the fcaps from the PATH record
> + * and use that to come up with the final set. Yeah, its ugly, but all the info
> + * is still in the audit log. So I'm not going to bother mentioning we failed
> + * if we couldn't allocate memory.
> + *
> + * If someone changes their mind they could create the aux record earlier and
> + * then search here and use that earlier allocation. But I don't wanna.
> + *
> + * -Eric
> + */
> +static inline void audit_log_bprm_fcaps(struct linux_binprm *bprm, kernel_cap_t *pP, kernel_cap_t *pE)
> +{
> + if (unlikely(!audit_dummy_context()))
> + __audit_log_bprm_fcaps(bprm, pP, pE);
> +}
> +
> extern int audit_n_rules;
> extern int audit_signals;
> #else
> @@ -532,6 +557,7 @@ extern int audit_signals;
> #define audit_mq_timedreceive(d,l,p,t) ({ 0; })
> #define audit_mq_notify(d,n) ({ 0; })
> #define audit_mq_getsetattr(d,s) ({ 0; })
> +#define audit_log_bprm_fcaps(b, p, e) do { ; } while (0)
> #define audit_ptrace(t) ((void)0)
> #define audit_n_rules 0
> #define audit_signals 0
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index f87f31a..b8b5a2a 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -196,6 +196,14 @@ struct audit_aux_data_pids {
> int pid_count;
> };
>
> +struct audit_aux_data_bprm_fcaps {
> + struct audit_aux_data d;
> + struct audit_cap_data fcap;
> + unsigned int fcap_ver;
> + struct audit_cap_data old_pcap;
> + struct audit_cap_data new_pcap;
> +};
> +
> struct audit_tree_refs {
> struct audit_tree_refs *next;
> struct audit_chunk *c[31];
> @@ -1375,6 +1383,20 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
> audit_log_format(ab, "fd0=%d fd1=%d", axs->fd[0], axs->fd[1]);
> break; }
>
> + case AUDIT_BPRM_FCAPS: {
> + struct audit_aux_data_bprm_fcaps *axs = (void *)aux;
> + audit_log_format(ab, "fver=%x", axs->fcap_ver);
> + audit_log_cap(ab, "fp", &axs->fcap.permitted);
> + audit_log_cap(ab, "fi", &axs->fcap.inheritable);
> + audit_log_format(ab, " fe=%d", axs->fcap.fE);
> + audit_log_cap(ab, "old_pp", &axs->old_pcap.permitted);
> + audit_log_cap(ab, "old_pi", &axs->old_pcap.inheritable);
> + audit_log_cap(ab, "old_pe", &axs->old_pcap.effective);
> + audit_log_cap(ab, "new_pp", &axs->new_pcap.permitted);
> + audit_log_cap(ab, "new_pi", &axs->new_pcap.inheritable);
> + audit_log_cap(ab, "new_pe", &axs->new_pcap.effective);
> + break; }
> +
> }
> audit_log_end(ab);
> }
> @@ -2502,6 +2524,52 @@ int __audit_signal_info(int sig, struct task_struct *t)
> }
>
> /**
> + * __audit_log_bprm_fcaps - store information about a loading bprm and relevant fcaps
> + * @bprm pointer to the bprm being processed
> + * @caps the caps read from the disk
> + *
> + * Simply check if the proc already has the caps given by the file and if not
> + * store the priv escalation info for later auditing at the end of the syscall
> + *
> + * this can fail and we don't care. See the note in audit.h for
> + * audit_log_bprm_fcaps() for my explaination....
> + *
> + * -Eric
> + */
> +void __audit_log_bprm_fcaps(struct linux_binprm *bprm, kernel_cap_t *pP, kernel_cap_t *pE)
> +{
> + struct audit_aux_data_bprm_fcaps *ax;
> + struct audit_context *context = current->audit_context;
> + struct cpu_vfs_cap_data vcaps;
> + struct dentry *dentry;
> +
> + ax = kmalloc(sizeof(*ax), GFP_KERNEL);
> + if (!ax)
> + return;
> +
> + ax->d.type = AUDIT_BPRM_FCAPS;
> + ax->d.next = context->aux;
> + context->aux = (void *)ax;
> +
> + dentry = dget(bprm->file->f_dentry);
> + get_vfs_caps_from_disk(dentry, &vcaps);
> + dput(dentry);
> +
> + ax->fcap.permitted = vcaps.permitted;
> + ax->fcap.inheritable = vcaps.inheritable;
> + ax->fcap.fE = !!(vcaps.magic_etc & VFS_CAP_FLAGS_EFFECTIVE);
> + ax->fcap_ver = (vcaps.magic_etc & VFS_CAP_REVISION_MASK) >> VFS_CAP_REVISION_SHIFT;
> +
> + ax->old_pcap.permitted = *pP;
> + ax->old_pcap.inheritable = current->cap_inheritable;
> + ax->old_pcap.effective = *pE;
> +
> + ax->new_pcap.permitted = current->cap_permitted;
> + ax->new_pcap.inheritable = current->cap_inheritable;
> + ax->new_pcap.effective = current->cap_effective;
> +}
> +
> +/**
> * audit_core_dumps - record information about processes that end abnormally
> * @signr: signal value
> *
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 8bb95ed..0b88160 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -8,6 +8,7 @@
> */
>
> #include <linux/capability.h>
> +#include <linux/audit.h>
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/kernel.h>
> @@ -373,6 +374,9 @@ int cap_bprm_set_security (struct linux_binprm *bprm)
>
> void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
> {
> + kernel_cap_t pP = current->cap_permitted;
> + kernel_cap_t pE = current->cap_effective;
> +
> if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
> !cap_issubset(bprm->cap_post_exec_permitted,
> current->cap_permitted)) {
> @@ -406,7 +410,24 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
> cap_clear(current->cap_effective);
> }
>
> - /* AUD: Audit candidate if current->cap_effective is set */
> + /*
> + * Audit candidate if current->cap_effective is set
> + *
> + * We do not bother to audit if 3 things are true:
> + * 1) cap_effective has all caps
> + * 2) we are root
> + * 3) root is supposed to have all caps (SECURE_NOROOT)
> + * Since this is just a normal root execing a process.
> + *
> + * Number 1 above might fail if you don't have a full bset, but I think
> + * that is interesting information to audit.
> + */
> + if (!cap_isclear(current->cap_effective)) {
> + if (!cap_issubset(CAP_FULL_SET, current->cap_effective) ||
> + (bprm->e_uid != 0) || (current->uid != 0) ||
> + issecure(SECURE_NOROOT))
> + audit_log_bprm_fcaps(bprm, &pP, &pE);
> + }
>
> current->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
> }