From: Serge E. Hallyn <serue@xxxxxxxxxx> Subject: [PATCH 1/2] file capabilities: implement file capabilities Implement file posix capabilities. This allows programs to be given a subset of root's powers regardless of who runs them, without having to use setuid and giving the binary all of root's powers. This version works with Kaigai Kohei's userspace tools, found at http://www.kaigai.gr.jp/index.php. For more information on how to use this patch, Chris Friedhoff has posted a nice page at http://www.friedhoff.org/fscaps.html. Changelog: Nov 27: Incorporate fixes from Andrew Morton (security-introduce-file-caps-tweaks and security-introduce-file-caps-warning-fix) Fix Kconfig dependency. Fix change signaling behavior when file caps are not compiled in. Nov 13: Integrate comments from Alexey: Remove CONFIG_ ifdef from capability.h, and use %zd for printing a size_t. Nov 13: Fix endianness warnings by sparse as suggested by Alexey Dobriyan. Nov 09: Address warnings of unused variables at cap_bprm_set_security when file capabilities are disabled, and simultaneously clean up the code a little, by pulling the new code into a helper function. Nov 08: For pointers to required userspace tools and how to use them, see http://www.friedhoff.org/fscaps.html. Nov 07: Fix the calculation of the highest bit checked in check_cap_sanity(). Nov 07: Allow file caps to be enabled without CONFIG_SECURITY, since capabilities are the default. Hook cap_task_setscheduler when !CONFIG_SECURITY. Move capable(TASK_KILL) to end of cap_task_kill to reduce audit messages. Nov 05: Add secondary calls in selinux/hooks.c to task_setioprio and task_setscheduler so that selinux and capabilities with file cap support can be stacked. Sep 05: As Seth Arnold points out, uid checks are out of place for capability code. Sep 01: Define task_setscheduler, task_setioprio, cap_task_kill, and task_setnice to make sure a user cannot affect a process in which they called a program with some fscaps. One remaining question is the note under task_setscheduler: are we ok with CAP_SYS_NICE being sufficient to confine a process to a cpuset? It is a semantic change, as without fsccaps, attach_task doesn't allow CAP_SYS_NICE to override the uid equivalence check. But since it uses security_task_setscheduler, which elsewhere is used where CAP_SYS_NICE can be used to override the uid equivalence check, fixing it might be tough. task_setscheduler note: this also controls cpuset:attach_task. Are we ok with CAP_SYS_NICE being used to confine to a cpuset? task_setioprio task_setnice sys_setpriority uses this (through set_one_prio) for another process. Need same checks as setrlimit Aug 21: Updated secureexec implementation to reflect the fact that euid and uid might be the same and nonzero, but the process might still have elevated caps. Aug 15: Handle endianness of xattrs. Enforce capability version match between kernel and disk. Enforce that no bits beyond the known max capability are set, else return -EPERM. With this extra processing, it may be worth reconsidering doing all the work at bprm_set_security rather than d_instantiate. Aug 10: Always call getxattr at bprm_set_security, rather than caching it at d_instantiate. Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx> Cc: Stephen Smalley <sds@xxxxxxxxxxxxx> Cc: James Morris <jmorris@xxxxxxxxx> Cc: Chris Wright <chrisw@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/capability.h | 20 +++ include/linux/security.h | 12 +- security/Kconfig | 10 + security/capability.c | 4 security/commoncap.c | 194 +++++++++++++++++++++++++++++++++-- security/selinux/hooks.c | 12 ++ 6 files changed, 241 insertions(+), 11 deletions(-) diff -puN include/linux/capability.h~implement-file-posix-capabilities include/linux/capability.h --- a/include/linux/capability.h~implement-file-posix-capabilities +++ a/include/linux/capability.h @@ -40,11 +40,29 @@ typedef struct __user_cap_data_struct { __u32 inheritable; } __user *cap_user_data_t; + + +#define XATTR_CAPS_SUFFIX "capability" +#define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX +struct vfs_cap_data_disk { + __le32 version; + __le32 effective; + __le32 permitted; + __le32 inheritable; +}; + #ifdef __KERNEL__ #include <linux/spinlock.h> #include <asm/current.h> +struct vfs_cap_data { + __u32 version; + __u32 effective; + __u32 permitted; + __u32 inheritable; +}; + /* #define STRICT_CAP_T_TYPECHECKS */ #ifdef STRICT_CAP_T_TYPECHECKS @@ -288,6 +306,8 @@ typedef __u32 kernel_cap_t; #define CAP_AUDIT_CONTROL 30 +#define CAP_NUMCAPS 31 + #ifdef __KERNEL__ /* * Bounding set diff -puN include/linux/security.h~implement-file-posix-capabilities include/linux/security.h --- a/include/linux/security.h~implement-file-posix-capabilities +++ a/include/linux/security.h @@ -53,6 +53,10 @@ extern int cap_inode_setxattr(struct den extern int cap_inode_removexattr(struct dentry *dentry, char *name); extern int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid, int flags); extern void cap_task_reparent_to_init (struct task_struct *p); +extern int cap_task_kill(struct task_struct *p, struct siginfo *info, int sig, u32 secid); +extern int cap_task_setscheduler (struct task_struct *p, int policy, struct sched_param *lp); +extern int cap_task_setioprio (struct task_struct *p, int ioprio); +extern int cap_task_setnice (struct task_struct *p, int nice); extern int cap_syslog (int type); extern int cap_vm_enough_memory (long pages); @@ -2585,12 +2589,12 @@ static inline int security_task_setgroup static inline int security_task_setnice (struct task_struct *p, int nice) { - return 0; + return cap_task_setnice(p, nice); } static inline int security_task_setioprio (struct task_struct *p, int ioprio) { - return 0; + return cap_task_setioprio(p, ioprio); } static inline int security_task_getioprio (struct task_struct *p) @@ -2608,7 +2612,7 @@ static inline int security_task_setsched int policy, struct sched_param *lp) { - return 0; + return cap_task_setscheduler(p, policy, lp); } static inline int security_task_getscheduler (struct task_struct *p) @@ -2625,7 +2629,7 @@ static inline int security_task_kill (st struct siginfo *info, int sig, u32 secid) { - return 0; + return cap_task_kill(p, info, sig, secid); } static inline int security_task_wait (struct task_struct *p) diff -puN security/Kconfig~implement-file-posix-capabilities security/Kconfig --- a/security/Kconfig~implement-file-posix-capabilities +++ a/security/Kconfig @@ -80,6 +80,16 @@ config SECURITY_CAPABILITIES This enables the "default" Linux capabilities functionality. If you are unsure how to answer this question, answer Y. +config SECURITY_FS_CAPABILITIES + bool "File POSIX Capabilities" + depends on SECURITY=n || SECURITY_CAPABILITIES=y + default n + help + This enables filesystem capabilities, allowing you to give + binaries a subset of root's powers without using setuid 0. + + If in doubt, answer N. + config SECURITY_ROOTPLUG tristate "Root Plug Support" depends on USB && SECURITY diff -puN security/capability.c~implement-file-posix-capabilities security/capability.c --- a/security/capability.c~implement-file-posix-capabilities +++ a/security/capability.c @@ -40,6 +40,10 @@ static struct security_operations capabi .inode_setxattr = cap_inode_setxattr, .inode_removexattr = cap_inode_removexattr, + .task_kill = cap_task_kill, + .task_setscheduler = cap_task_setscheduler, + .task_setioprio = cap_task_setioprio, + .task_setnice = cap_task_setnice, .task_post_setuid = cap_task_post_setuid, .task_reparent_to_init = cap_task_reparent_to_init, diff -puN security/commoncap.c~implement-file-posix-capabilities security/commoncap.c --- a/security/commoncap.c~implement-file-posix-capabilities +++ a/security/commoncap.c @@ -23,6 +23,7 @@ #include <linux/ptrace.h> #include <linux/xattr.h> #include <linux/hugetlb.h> +#include <linux/mount.h> int cap_netlink_send(struct sock *sk, struct sk_buff *skb) { @@ -109,15 +110,108 @@ void cap_capset_set (struct task_struct target->cap_permitted = *permitted; } +#ifdef CONFIG_SECURITY_FS_CAPABILITIES +static inline void cap_from_disk(struct vfs_cap_data_disk *dcap, + struct vfs_cap_data *cap) +{ + cap->version = le32_to_cpu(dcap->version); + cap->effective = le32_to_cpu(dcap->effective); + cap->permitted = le32_to_cpu(dcap->permitted); + cap->inheritable = le32_to_cpu(dcap->inheritable); +} + +static int check_cap_sanity(struct vfs_cap_data *cap) +{ + int i; + + if (cap->version != _LINUX_CAPABILITY_VERSION) + return -EPERM; + + for (i = CAP_NUMCAPS; i < 8*sizeof(cap->effective); i++) { + if (cap->effective & CAP_TO_MASK(i)) + return -EPERM; + } + for (i = CAP_NUMCAPS; i < 8*sizeof(cap->permitted); i++) { + if (cap->permitted & CAP_TO_MASK(i)) + return -EPERM; + } + for (i = CAP_NUMCAPS; i < 8*sizeof(cap->inheritable); i++) { + if (cap->inheritable & CAP_TO_MASK(i)) + return -EPERM; + } + + return 0; +} + +/* Locate any VFS capabilities: */ +static int set_file_caps(struct linux_binprm *bprm) +{ + struct dentry *dentry; + ssize_t rc; + struct vfs_cap_data_disk dcaps; + struct vfs_cap_data caps; + struct inode *inode; + int err; + + if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID) + return 0; + + dentry = dget(bprm->file->f_dentry); + inode = dentry->d_inode; + if (!inode->i_op || !inode->i_op->getxattr) { + dput(dentry); + return 0; + } + + rc = inode->i_op->getxattr(dentry, XATTR_NAME_CAPS, &dcaps, + sizeof(dcaps)); + dput(dentry); + + if (rc == -ENODATA) + return 0; + + if (rc < 0) { + printk(KERN_NOTICE "%s: Error (%zd) getting xattr\n", + __FUNCTION__, rc); + return rc; + } + + if (rc != sizeof(dcaps)) { + printk(KERN_NOTICE "%s: got wrong size for getxattr (%zd)\n", + __FUNCTION__, rc); + return -EPERM; + } + + cap_from_disk(&dcaps, &caps); + err = check_cap_sanity(&caps); + if (err) + return err; + + bprm->cap_effective = caps.effective; + bprm->cap_permitted = caps.permitted; + bprm->cap_inheritable = caps.inheritable; + + return 0; +} +#else +static inline int set_file_caps(struct linux_binprm *bprm) +{ + return 0; +} +#endif + int cap_bprm_set_security (struct linux_binprm *bprm) { + int ret; + /* Copied from fs/exec.c:prepare_binprm. */ - /* We don't have VFS support for capabilities yet */ cap_clear (bprm->cap_inheritable); cap_clear (bprm->cap_permitted); cap_clear (bprm->cap_effective); + ret = set_file_caps(bprm); + /* To support inheritance of root-permissions and suid-root * executables under compatibility mode, we raise all three * capability sets for the file. @@ -134,7 +228,8 @@ int cap_bprm_set_security (struct linux_ if (bprm->e_uid == 0) cap_set_full (bprm->cap_effective); } - return 0; + + return ret; } void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe) @@ -182,11 +277,15 @@ void cap_bprm_apply_creds (struct linux_ int cap_bprm_secureexec (struct linux_binprm *bprm) { - /* If/when this module is enhanced to incorporate capability - bits on files, the test below should be extended to also perform a - test between the old and new capability sets. For now, - it simply preserves the legacy decision algorithm used by - the old userland. */ + if (current->uid != 0) { + if (!cap_isclear(bprm->cap_effective)) + return 1; + if (!cap_isclear(bprm->cap_permitted)) + return 1; + if (!cap_isclear(bprm->cap_inheritable)) + return 1; + } + return (current->euid != current->uid || current->egid != current->gid); } @@ -300,6 +399,83 @@ int cap_task_post_setuid (uid_t old_ruid return 0; } +#ifdef CONFIG_SECURITY_FS_CAPABILITIES +/* + * Rationale: code calling task_setscheduler, task_setioprio, and + * task_setnice, assumes that + * . if capable(cap_sys_nice), then those actions should be allowed + * . if not capable(cap_sys_nice), but acting on your own processes, + * then those actions should be allowed + * This is insufficient now since you can call code without suid, but + * yet with increased caps. + * So we check for increased caps on the target process. + */ +static inline int cap_safe_nice(struct task_struct *p) +{ + if (!cap_issubset(p->cap_permitted, current->cap_permitted) && + !__capable(current, CAP_SYS_NICE)) + return -EPERM; + return 0; +} + +int cap_task_setscheduler (struct task_struct *p, int policy, + struct sched_param *lp) +{ + return cap_safe_nice(p); +} + +int cap_task_setioprio (struct task_struct *p, int ioprio) +{ + return cap_safe_nice(p); +} + +int cap_task_setnice (struct task_struct *p, int nice) +{ + return cap_safe_nice(p); +} + +int cap_task_kill(struct task_struct *p, struct siginfo *info, + int sig, u32 secid) +{ + if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info))) + return 0; + + if (secid) + /* + * Signal sent as a particular user. + * Capabilities are ignored. May be wrong, but it's the + * only thing we can do at the moment. + * Used only by usb drivers? + */ + return 0; + if (cap_issubset(p->cap_permitted, current->cap_permitted)) + return 0; + if (capable(CAP_KILL)) + return 0; + + return -EPERM; +} +#else +int cap_task_setscheduler (struct task_struct *p, int policy, + struct sched_param *lp) +{ + return 0; +} +int cap_task_setioprio (struct task_struct *p, int ioprio) +{ + return 0; +} +int cap_task_setnice (struct task_struct *p, int nice) +{ + return 0; +} +int cap_task_kill(struct task_struct *p, struct siginfo *info, + int sig, u32 secid) +{ + return 0; +} +#endif + void cap_task_reparent_to_init (struct task_struct *p) { p->cap_effective = CAP_INIT_EFF_SET; @@ -337,6 +513,10 @@ EXPORT_SYMBOL(cap_bprm_secureexec); EXPORT_SYMBOL(cap_inode_setxattr); EXPORT_SYMBOL(cap_inode_removexattr); EXPORT_SYMBOL(cap_task_post_setuid); +EXPORT_SYMBOL(cap_task_kill); +EXPORT_SYMBOL(cap_task_setscheduler); +EXPORT_SYMBOL(cap_task_setioprio); +EXPORT_SYMBOL(cap_task_setnice); EXPORT_SYMBOL(cap_task_reparent_to_init); EXPORT_SYMBOL(cap_syslog); EXPORT_SYMBOL(cap_vm_enough_memory); diff -puN security/selinux/hooks.c~implement-file-posix-capabilities security/selinux/hooks.c --- a/security/selinux/hooks.c~implement-file-posix-capabilities +++ a/security/selinux/hooks.c @@ -2825,6 +2825,12 @@ static int selinux_task_setnice(struct t static int selinux_task_setioprio(struct task_struct *p, int ioprio) { + int rc; + + rc = secondary_ops->task_setioprio(p, ioprio); + if (rc) + return rc; + return task_has_perm(current, p, PROCESS__SETSCHED); } @@ -2854,6 +2860,12 @@ static int selinux_task_setrlimit(unsign static int selinux_task_setscheduler(struct task_struct *p, int policy, struct sched_param *lp) { + int rc; + + rc = secondary_ops->task_setscheduler(p, policy, lp); + if (rc) + return rc; + return task_has_perm(current, p, PROCESS__SETSCHED); } _ - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
