From 0c736c9f0ab16899df1803d5962287985e69a157 Mon Sep 17 00:00:00 2001 From: Andrew G. Morgan Date: Mon, 26 May 2008 18:06:27 -0700 Subject: [PATCH] Remain source compatible with 32-bit raw legacy capability support. Source code out there hard-codes a notion of what the _LINUX_CAPABILITY_VERSION #define means in terms of the semantics of the raw capability system calls capget() and capset(). Its unfortunate, but true. Since the confusing header file has been in a released kernel, there is software that is erroneously using 64-bit capabilities with the semantics of 32-bit compatibilities. These recently compiled programs may suffer corruption of their memory when sys_getcap() overwrites more memory than they are coded to expect, and the raising of added capabilities when using sys_capset(). As such, this patch does a number of things to clean up the situation for all. It 1. forces the _LINUX_CAPABILITY_VERSION define to always retain its legacy value. 2. adopts a new #define strategy for the kernel's internal implementation of the preferred magic. 3. depreciates v2 capability magic in favor of a new (v3) magic number. The functionality of v3 is entirely equivalent to v2, the only difference being that the v2 magic causes the kernel to log a "depreciated" warning so the admin can find applications that may be using v2 inappropriately. [User space code continues to be encouraged to use the libcap API which protects the application from details like this. libcap-2.10 is the first to support v3 capabilities.] Signed-off-by: Andrew G. Morgan Cc: Andrew Morton Cc: Chris Wright Cc: Serge E. Hallyn --- fs/proc/array.c | 2 +- include/linux/capability.h | 29 ++++++++--- kernel/capability.c | 110 +++++++++++++++++++++++++++++--------------- 3 files changed, 94 insertions(+), 47 deletions(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 9e3b8c3..797d775 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -288,7 +288,7 @@ static void render_cap_t(struct seq_file *m, const char *header, seq_printf(m, "%s", header); CAP_FOR_EACH_U32(__capi) { seq_printf(m, "%08x", - a->cap[(_LINUX_CAPABILITY_U32S-1) - __capi]); + a->cap[(_KERNEL_CAPABILITY_U32S-1) - __capi]); } seq_printf(m, "\n"); } diff --git a/include/linux/capability.h b/include/linux/capability.h index f4ea0dd..272e040 100644 --- a/include/linux/capability.h +++ b/include/linux/capability.h @@ -31,11 +31,11 @@ struct task_struct; #define _LINUX_CAPABILITY_VERSION_1 0x19980330 #define _LINUX_CAPABILITY_U32S_1 1 -#define _LINUX_CAPABILITY_VERSION_2 0x20071026 +#define _LINUX_CAPABILITY_VERSION_2 0x20071026 /* depreciated - use v3 */ #define _LINUX_CAPABILITY_U32S_2 2 -#define _LINUX_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_2 -#define _LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_2 +#define _LINUX_CAPABILITY_VERSION_3 0x20080522 +#define _LINUX_CAPABILITY_U32S_3 2 typedef struct __user_cap_header_struct { __u32 version; @@ -77,10 +77,23 @@ struct vfs_cap_data { } data[VFS_CAP_U32]; }; -#ifdef __KERNEL__ +#ifndef __KERNEL__ + +/* + * Backwardly compatible definition for source code - trapped in a + * 32-bit world. If you find you need this, please consider using + * libcap to untrap yourself... + */ +#define _LINUX_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_1 +#define _LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_1 + +#else + +#define _KERNEL_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_3 +#define _KERNEL_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3 typedef struct kernel_cap_struct { - __u32 cap[_LINUX_CAPABILITY_U32S]; + __u32 cap[_KERNEL_CAPABILITY_U32S]; } kernel_cap_t; #define _USER_CAP_HEADER_SIZE (sizeof(struct __user_cap_header_struct)) @@ -351,7 +364,7 @@ typedef struct kernel_cap_struct { */ #define CAP_FOR_EACH_U32(__capi) \ - for (__capi = 0; __capi < _LINUX_CAPABILITY_U32S; ++__capi) + for (__capi = 0; __capi < _KERNEL_CAPABILITY_U32S; ++__capi) # define CAP_FS_MASK_B0 (CAP_TO_MASK(CAP_CHOWN) \ | CAP_TO_MASK(CAP_DAC_OVERRIDE) \ @@ -361,7 +374,7 @@ typedef struct kernel_cap_struct { # define CAP_FS_MASK_B1 (CAP_TO_MASK(CAP_MAC_OVERRIDE)) -#if _LINUX_CAPABILITY_U32S != 2 +#if _KERNEL_CAPABILITY_U32S != 2 # error Fix up hand-coded capability macro initializers #else /* HAND-CODED capability initializers */ @@ -372,7 +385,7 @@ typedef struct kernel_cap_struct { # define CAP_NFSD_SET ((kernel_cap_t){{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), \ CAP_FS_MASK_B1 } }) -#endif /* _LINUX_CAPABILITY_U32S != 2 */ +#endif /* _KERNEL_CAPABILITY_U32S != 2 */ #define CAP_INIT_INH_SET CAP_EMPTY_SET diff --git a/kernel/capability.c b/kernel/capability.c index 39e8193..326406c 100644 --- a/kernel/capability.c +++ b/kernel/capability.c @@ -53,6 +53,68 @@ static void warn_legacy_capability_use(void) } /* + * Version 2 capabilities worked fine, but the linux/capability.h file + * that accompanied their introduction encouraged their use without + * the necessary user-space source code changes. As such, we have + * created a version 3 with equivalent functionality to version 2, but + * with a header change to protect legacy source code from using + * version 2 when it wanted to use version 1. If your system has code + * that trips the following warning, it is using version 2 specific + * capabilities and may be doing so insecurely. + * + * The remedy is to either upgrade your version of libcap (to 2.10+, + * if the application is linked against it), or recompile your + * application with modern kernel headers and this warning will go + * away. + */ + +static void warn_depreciated_v2(void) +{ + static int warned = 0; + if (!warned) { + char name[sizeof(current->comm)]; + + printk(KERN_INFO "warning: `%s' uses depreciated v2" + " capabilities in a way that may be insecure.\n", + get_task_comm(name, current)); + warned = 1; + } +} + +/* + * Version check. Return the number of u32s in each capability flag + * array, or a negative value on error. + */ +static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy) +{ + __u32 version; + + if (get_user(version, &header->version)) + return -EFAULT; + + switch (version) { + case _LINUX_CAPABILITY_VERSION_1: + warn_legacy_capability_use(); + *tocopy = _LINUX_CAPABILITY_U32S_1; + break; + case _LINUX_CAPABILITY_VERSION_2: + warn_depreciated_v2(); + /* + * fall through - v3 is otherwise equivalent to v2. + */ + case _LINUX_CAPABILITY_VERSION_3: + *tocopy = _LINUX_CAPABILITY_U32S_3; + break; + default: + if (put_user(_KERNEL_CAPABILITY_VERSION, &header->version)) + return -EFAULT; + return -EINVAL; + } + + return 0; +} + +/* * For sys_getproccap() and sys_setproccap(), any of the three * capability set pointers may be NULL -- indicating that that set is * uninteresting and/or not to be changed. @@ -71,27 +133,13 @@ asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr) { int ret = 0; pid_t pid; - __u32 version; struct task_struct *target; unsigned tocopy; kernel_cap_t pE, pI, pP; - if (get_user(version, &header->version)) - return -EFAULT; - - switch (version) { - case _LINUX_CAPABILITY_VERSION_1: - warn_legacy_capability_use(); - tocopy = _LINUX_CAPABILITY_U32S_1; - break; - case _LINUX_CAPABILITY_VERSION_2: - tocopy = _LINUX_CAPABILITY_U32S_2; - break; - default: - if (put_user(_LINUX_CAPABILITY_VERSION, &header->version)) - return -EFAULT; - return -EINVAL; - } + ret = cap_validate_magic(header, &tocopy); + if (ret != 0) + return ret; if (get_user(pid, &header->pid)) return -EFAULT; @@ -118,7 +166,7 @@ out: spin_unlock(&task_capability_lock); if (!ret) { - struct __user_cap_data_struct kdata[_LINUX_CAPABILITY_U32S]; + struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S]; unsigned i; for (i = 0; i < tocopy; i++) { @@ -128,7 +176,7 @@ out: } /* - * Note, in the case, tocopy < _LINUX_CAPABILITY_U32S, + * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S, * we silently drop the upper capabilities here. This * has the effect of making older libcap * implementations implicitly drop upper capability @@ -240,30 +288,16 @@ static inline int cap_set_all(kernel_cap_t *effective, */ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data) { - struct __user_cap_data_struct kdata[_LINUX_CAPABILITY_U32S]; + struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S]; unsigned i, tocopy; kernel_cap_t inheritable, permitted, effective; - __u32 version; struct task_struct *target; int ret; pid_t pid; - if (get_user(version, &header->version)) - return -EFAULT; - - switch (version) { - case _LINUX_CAPABILITY_VERSION_1: - warn_legacy_capability_use(); - tocopy = _LINUX_CAPABILITY_U32S_1; - break; - case _LINUX_CAPABILITY_VERSION_2: - tocopy = _LINUX_CAPABILITY_U32S_2; - break; - default: - if (put_user(_LINUX_CAPABILITY_VERSION, &header->version)) - return -EFAULT; - return -EINVAL; - } + ret = cap_validate_magic(header, &tocopy); + if (ret != 0) + return ret; if (get_user(pid, &header->pid)) return -EFAULT; @@ -281,7 +315,7 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data) permitted.cap[i] = kdata[i].permitted; inheritable.cap[i] = kdata[i].inheritable; } - while (i < _LINUX_CAPABILITY_U32S) { + while (i < _KERNEL_CAPABILITY_U32S) { effective.cap[i] = 0; permitted.cap[i] = 0; inheritable.cap[i] = 0; -- 1.5.3.7