"Serge E. Hallyn" <[email protected]> writes: > Quoting Eric W. Biederman ([email protected]): >> >> Serge, >> >> Is there any change of a Signed-off-by on this patch? Otherwise I don't >> think we can merge it. > > For pete's sake! I'm sorry, i seem to remember with just about every > other project other than this. particular. patch. > > Does this > > Signed-off-by: Serge Hallyn <[email protected]> > > suffice, or should I resend?
Good enough for me. I figured it was an oversight but I had to check. Eric >> "Serge E. Hallyn" <[email protected]> writes: >> >> > Root in a non-initial user ns cannot be trusted to write a traditional >> > security.capability xattr. If it were allowed to do so, then any >> > unprivileged user on the host could map his own uid to root in a private >> > namespace, write the xattr, and execute the file with privilege on the >> > host. >> > >> > However supporting file capabilities in a user namespace is very >> > desirable. Not doing so means that any programs designed to run with >> > limited privilege must continue to support other methods of gaining and >> > dropping privilege. For instance a program installer must detect >> > whether file capabilities can be assigned, and assign them if so but set >> > setuid-root otherwise. The program in turn must know how to drop >> > partial capabilities, and do so only if setuid-root. >> > >> > This patch introduces v3 of the security.capability xattr. It builds a >> > vfs_ns_cap_data struct by appending a uid_t rootid to struct >> > vfs_cap_data. This is the absolute uid_t (that is, the uid_t in user >> > namespace which mounted the filesystem, usually init_user_ns) of the >> > root id in whose namespaces the file capabilities may take effect. >> > >> > When a task asks to write a v2 security.capability xattr, if it is >> > privileged with respect to the userns which mounted the filesystem, then >> > nothing should change. Otherwise, the kernel will transparently rewrite >> > the xattr as a v3 with the appropriate rootid. Subsequently, any task >> > executing the file which has the noted kuid as its root uid, or which is >> > in a descendent user_ns of such a user_ns, will run the file with >> > capabilities. >> > >> > Similarly when asking to read file capabilities, a v3 capability will >> > be presented as v2 if it applies to the caller's namespace. >> > >> > If a task writes a v3 security.capability, then it can provide a uid for >> > the xattr so long as the uid is valid in its own user namespace, and it >> > is privileged with CAP_SETFCAP over its namespace. The kernel will >> > translate that rootid to an absolute uid, and write that to disk. After >> > this, a task in the writer's namespace will not be able to use those >> > capabilities (unless rootid was 0), but a task in a namespace where the >> > given uid is root will. >> > >> > Only a single security.capability xattr may exist at a time for a given >> > file. A task may overwrite an existing xattr so long as it is >> > privileged over the inode. Note this is a departure from previous >> > semantics, which required privilege to remove a security.capability >> > xattr. This check can be re-added if deemed useful. >> > >> > This allows a simple setcap/setxattr to work, should allow tar to work, >> > and should allow us to support tar in one namespace and untar in another >> > while preserving the capability, without risking leaking privilege into >> > a parent namespace. >> > >> > A patch to linux-test-project adding a new set of tests for this >> > functionality is in the nsfscaps branch at github.com/hallyn/ltp >> > >> > Changelog: >> > Nov 02 2016: fix invalid check at refuse_fcap_overwrite() >> > Nov 07 2016: convert rootid from and to fs user_ns >> > (From ebiederm: mar 28 2017) >> > commoncap.c: fix typos - s/v4/v3 >> > get_vfs_caps_from_disk: clarify the fs_ns root access check >> > nsfscaps: change the code split for cap_inode_setxattr() >> > Apr 09 2017: >> > don't return v3 cap for caps owned by current root. >> > return a v2 cap for a true v2 cap in non-init ns >> > Apr 18 2017: >> > . Change the flow of fscap writing to support s_user_ns writing. >> > . Remove refuse_fcap_overwrite(). The value of the previous >> > xattr doesn't matter. >> > --- >> > fs/xattr.c | 30 ++++- >> > include/linux/capability.h | 5 +- >> > include/linux/security.h | 2 + >> > include/uapi/linux/capability.h | 22 +++- >> > security/commoncap.c | 237 >> > ++++++++++++++++++++++++++++++++++++---- >> > 5 files changed, 268 insertions(+), 28 deletions(-) >> > >> > diff --git a/fs/xattr.c b/fs/xattr.c >> > index 7e3317c..75cc65a 100644 >> > --- a/fs/xattr.c >> > +++ b/fs/xattr.c >> > @@ -170,12 +170,29 @@ int __vfs_setxattr_noperm(struct dentry *dentry, >> > const char *name, >> > const void *value, size_t size, int flags) >> > { >> > struct inode *inode = dentry->d_inode; >> > - int error = -EAGAIN; >> > + int error; >> > + void *wvalue = NULL; >> > + size_t wsize = 0; >> > int issec = !strncmp(name, XATTR_SECURITY_PREFIX, >> > XATTR_SECURITY_PREFIX_LEN); >> > >> > - if (issec) >> > + if (issec) { >> > inode->i_flags &= ~S_NOSEC; >> > + >> > + if (!strcmp(name, "security.capability")) { >> > + error = cap_setxattr_convert_nscap(dentry, value, size, >> > + &wvalue, &wsize); >> > + if (error < 0) >> > + return error; >> > + if (wvalue) { >> > + value = wvalue; >> > + size = wsize; >> > + } >> > + } >> > + } >> > + >> > + error = -EAGAIN; >> > + >> > if (inode->i_opflags & IOP_XATTR) { >> > error = __vfs_setxattr(dentry, inode, name, value, size, flags); >> > if (!error) { >> > @@ -184,8 +201,10 @@ int __vfs_setxattr_noperm(struct dentry *dentry, >> > const char *name, >> > size, flags); >> > } >> > } else { >> > - if (unlikely(is_bad_inode(inode))) >> > - return -EIO; >> > + if (unlikely(is_bad_inode(inode))) { >> > + error = -EIO; >> > + goto out; >> > + } >> > } >> > if (error == -EAGAIN) { >> > error = -EOPNOTSUPP; >> > @@ -200,10 +219,11 @@ int __vfs_setxattr_noperm(struct dentry *dentry, >> > const char *name, >> > } >> > } >> > >> > +out: >> > + kfree(wvalue); >> > return error; >> > } >> > >> > - >> > int >> > vfs_setxattr(struct dentry *dentry, const char *name, const void *value, >> > size_t size, int flags) >> > diff --git a/include/linux/capability.h b/include/linux/capability.h >> > index 6ffb67e..b973433 100644 >> > --- a/include/linux/capability.h >> > +++ b/include/linux/capability.h >> > @@ -13,7 +13,7 @@ >> > #define _LINUX_CAPABILITY_H >> > >> > #include <uapi/linux/capability.h> >> > - >> > +#include <linux/uidgid.h> >> > >> > #define _KERNEL_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_3 >> > #define _KERNEL_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3 >> > @@ -248,4 +248,7 @@ extern bool ptracer_capable(struct task_struct *tsk, >> > struct user_namespace *ns); >> > /* audit system wants to get cap info from files as well */ >> > extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct >> > cpu_vfs_cap_data *cpu_caps); >> > >> > +extern int cap_setxattr_convert_nscap(struct dentry *dentry, const void >> > *value, >> > + size_t size, void **wvalue, size_t *wsize); >> > + >> > #endif /* !_LINUX_CAPABILITY_H */ >> > diff --git a/include/linux/security.h b/include/linux/security.h >> > index 96899fa..bd49cc1 100644 >> > --- a/include/linux/security.h >> > +++ b/include/linux/security.h >> > @@ -86,6 +86,8 @@ extern int cap_inode_setxattr(struct dentry *dentry, >> > const char *name, >> > extern int cap_inode_removexattr(struct dentry *dentry, const char *name); >> > extern int cap_inode_need_killpriv(struct dentry *dentry); >> > extern int cap_inode_killpriv(struct dentry *dentry); >> > +extern int cap_inode_getsecurity(struct inode *inode, const char *name, >> > + void **buffer, bool alloc); >> > extern int cap_mmap_addr(unsigned long addr); >> > extern int cap_mmap_file(struct file *file, unsigned long reqprot, >> > unsigned long prot, unsigned long flags); >> > diff --git a/include/uapi/linux/capability.h >> > b/include/uapi/linux/capability.h >> > index 49bc062..fd4f87d 100644 >> > --- a/include/uapi/linux/capability.h >> > +++ b/include/uapi/linux/capability.h >> > @@ -60,9 +60,13 @@ typedef struct __user_cap_data_struct { >> > #define VFS_CAP_U32_2 2 >> > #define XATTR_CAPS_SZ_2 (sizeof(__le32)*(1 + 2*VFS_CAP_U32_2)) >> > >> > -#define XATTR_CAPS_SZ XATTR_CAPS_SZ_2 >> > -#define VFS_CAP_U32 VFS_CAP_U32_2 >> > -#define VFS_CAP_REVISION VFS_CAP_REVISION_2 >> > +#define VFS_CAP_REVISION_3 0x03000000 >> > +#define VFS_CAP_U32_3 2 >> > +#define XATTR_CAPS_SZ_3 (sizeof(__le32)*(2 + 2*VFS_CAP_U32_3)) >> > + >> > +#define XATTR_CAPS_SZ XATTR_CAPS_SZ_3 >> > +#define VFS_CAP_U32 VFS_CAP_U32_3 >> > +#define VFS_CAP_REVISION VFS_CAP_REVISION_3 >> > >> > struct vfs_cap_data { >> > __le32 magic_etc; /* Little endian */ >> > @@ -72,6 +76,18 @@ struct vfs_cap_data { >> > } data[VFS_CAP_U32]; >> > }; >> > >> > +/* >> > + * same as vfs_cap_data but with a rootid at the end >> > + */ >> > +struct vfs_ns_cap_data { >> > + __le32 magic_etc; >> > + struct { >> > + __le32 permitted; /* Little endian */ >> > + __le32 inheritable; /* Little endian */ >> > + } data[VFS_CAP_U32]; >> > + __le32 rootid; >> > +}; >> > + >> > #ifndef __KERNEL__ >> > >> > /* >> > diff --git a/security/commoncap.c b/security/commoncap.c >> > index 78b3783..8abb9bf 100644 >> > --- a/security/commoncap.c >> > +++ b/security/commoncap.c >> > @@ -332,6 +332,179 @@ int cap_inode_killpriv(struct dentry *dentry) >> > return error; >> > } >> > >> > +static bool rootid_owns_currentns(kuid_t kroot) >> > +{ >> > + struct user_namespace *ns; >> > + >> > + if (!uid_valid(kroot)) >> > + return false; >> > + >> > + for (ns = current_user_ns(); ; ns = ns->parent) { >> > + if (from_kuid(ns, kroot) == 0) >> > + return true; >> > + if (ns == &init_user_ns) >> > + break; >> > + } >> > + >> > + return false; >> > +} >> > + >> > +/* >> > + * getsecurity: We are called for security.* before any attempt to read >> > the >> > + * xattr from the inode itself. >> > + * >> > + * This gives us a chance to read the on-disk value and convert it. If we >> > + * return -EOPNOTSUPP, then vfs_getxattr() will call the i_op handler. >> > + * >> > + * Note we are not called by vfs_getxattr_alloc(), but that is only called >> > + * by the integrity subsystem, which really wants the unconverted values - >> > + * so that's good. >> > + */ >> > +int cap_inode_getsecurity(struct inode *inode, const char *name, void >> > **buffer, >> > + bool alloc) >> > +{ >> > + int size, ret; >> > + kuid_t kroot; >> > + uid_t root, mappedroot; >> > + char *tmpbuf = NULL; >> > + struct vfs_ns_cap_data *nscap; >> > + struct dentry *dentry; >> > + struct user_namespace *fs_ns; >> > + >> > + if (strcmp(name, "capability") != 0) >> > + return -EOPNOTSUPP; >> > + >> > + dentry = d_find_alias(inode); >> > + if (!dentry) >> > + return -EINVAL; >> > + >> > + size = sizeof(struct vfs_ns_cap_data); >> > + ret = vfs_getxattr_alloc(dentry, "security.capability", >> > + &tmpbuf, size, GFP_NOFS); >> > + >> > + if (ret < 0) >> > + return ret; >> > + >> > + fs_ns = inode->i_sb->s_user_ns; >> > + if (ret == sizeof(struct vfs_cap_data)) { >> > + /* If this is sizeof(vfs_cap_data) then we're ok with the >> > + * on-disk value, so return that. */ >> > + if (alloc) >> > + *buffer = tmpbuf; >> > + else >> > + kfree(tmpbuf); >> > + return ret; >> > + } else if (ret != sizeof(struct vfs_ns_cap_data)) { >> > + kfree(tmpbuf); >> > + return -EINVAL; >> > + } >> > + >> > + nscap = (struct vfs_ns_cap_data *) tmpbuf; >> > + root = le32_to_cpu(nscap->rootid); >> > + kroot = make_kuid(fs_ns, root); >> > + >> > + /* If the root kuid maps to a valid uid in current ns, then return >> > + * this as a nscap. */ >> > + mappedroot = from_kuid(current_user_ns(), kroot); >> > + if (mappedroot != (uid_t)-1 && mappedroot != (uid_t)0) { >> > + if (alloc) { >> > + *buffer = tmpbuf; >> > + nscap->rootid = cpu_to_le32(mappedroot); >> > + } else >> > + kfree(tmpbuf); >> > + return size; >> > + } >> > + >> > + if (!rootid_owns_currentns(kroot)) { >> > + kfree(tmpbuf); >> > + return -EOPNOTSUPP; >> > + } >> > + >> > + /* This comes from a parent namespace. Return as a v2 capability */ >> > + size = sizeof(struct vfs_cap_data); >> > + if (alloc) { >> > + *buffer = kmalloc(size, GFP_ATOMIC); >> > + if (*buffer) { >> > + struct vfs_cap_data *cap = *buffer; >> > + __le32 nsmagic, magic; >> > + magic = VFS_CAP_REVISION_2; >> > + nsmagic = le32_to_cpu(nscap->magic_etc); >> > + if (nsmagic & VFS_CAP_FLAGS_EFFECTIVE) >> > + magic |= VFS_CAP_FLAGS_EFFECTIVE; >> > + memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * >> > VFS_CAP_U32); >> > + cap->magic_etc = cpu_to_le32(magic); >> > + } >> > + } >> > + kfree(tmpbuf); >> > + return size; >> > +} >> > + >> > +static kuid_t rootid_from_xattr(const void *value, size_t size, >> > + struct user_namespace *task_ns) >> > +{ >> > + const struct vfs_ns_cap_data *nscap = value; >> > + uid_t rootid = 0; >> > + >> > + if (size == XATTR_CAPS_SZ_3) >> > + rootid = le32_to_cpu(nscap->rootid); >> > + >> > + return make_kuid(task_ns, rootid); >> > +} >> > + >> > +/* >> > + * User requested a write of security.capability. >> > + * >> > + * If all is ok, we return 0. If the capability needs to be converted, >> > + * wvalue will be allocated (and needs to be freed) with the new value. >> > + * On error, return < 0. >> > + */ >> > +int cap_setxattr_convert_nscap(struct dentry *dentry, const void *value, >> > size_t size, >> > + void **wvalue, size_t *wsize) >> > +{ >> > + struct vfs_ns_cap_data *nscap; >> > + uid_t nsrootid; >> > + const struct vfs_cap_data *cap = value; >> > + __u32 magic, nsmagic; >> > + struct inode *inode = d_backing_inode(dentry); >> > + struct user_namespace *task_ns = current_user_ns(), >> > + *fs_ns = inode->i_sb->s_user_ns; >> > + kuid_t rootid; >> > + >> > + if (!value) >> > + return -EINVAL; >> > + if (size != XATTR_CAPS_SZ_2 && size != XATTR_CAPS_SZ_3) >> > + return -EINVAL; >> > + if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP)) >> > + return -EPERM; >> > + if (size == XATTR_CAPS_SZ_2) >> > + if (ns_capable(inode->i_sb->s_user_ns, CAP_SETFCAP)) >> > + // user is privileged, just write the v2 >> > + return 0; >> > + >> > + rootid = rootid_from_xattr(value, size, task_ns); >> > + if (!uid_valid(rootid)) >> > + return -EINVAL; >> > + >> > + nsrootid = from_kuid(fs_ns, rootid); >> > + if (nsrootid == -1) >> > + return -EINVAL; >> > + >> > + *wsize = sizeof(struct vfs_ns_cap_data); >> > + nscap = kmalloc(*wsize, GFP_ATOMIC); >> > + if (!nscap) >> > + return -ENOMEM; >> > + nscap->rootid = cpu_to_le32(nsrootid); >> > + nsmagic = VFS_CAP_REVISION_3; >> > + magic = le32_to_cpu(cap->magic_etc); >> > + if (magic & VFS_CAP_FLAGS_EFFECTIVE) >> > + nsmagic |= VFS_CAP_FLAGS_EFFECTIVE; >> > + nscap->magic_etc = cpu_to_le32(nsmagic); >> > + memcpy(&nscap->data, &cap->data, sizeof(__le32) * 2 * VFS_CAP_U32); >> > + >> > + *wvalue = nscap; >> > + return 0; >> > +} >> > + >> > /* >> > * Calculate the new process capability sets from the capability sets >> > attached >> > * to a file. >> > @@ -385,7 +558,10 @@ int get_vfs_caps_from_disk(const struct dentry >> > *dentry, struct cpu_vfs_cap_data >> > __u32 magic_etc; >> > unsigned tocopy, i; >> > int size; >> > - struct vfs_cap_data caps; >> > + struct vfs_ns_cap_data data, *nscaps = &data; >> > + struct vfs_cap_data *caps = (struct vfs_cap_data *) &data; >> > + kuid_t rootkuid; >> > + struct user_namespace *fs_ns = inode->i_sb->s_user_ns; >> > >> > memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data)); >> > >> > @@ -393,18 +569,20 @@ int get_vfs_caps_from_disk(const struct dentry >> > *dentry, struct cpu_vfs_cap_data >> > return -ENODATA; >> > >> > size = __vfs_getxattr((struct dentry *)dentry, inode, >> > - XATTR_NAME_CAPS, &caps, XATTR_CAPS_SZ); >> > + XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ); >> > if (size == -ENODATA || size == -EOPNOTSUPP) >> > /* no data, that's ok */ >> > return -ENODATA; >> > + >> > if (size < 0) >> > return size; >> > >> > if (size < sizeof(magic_etc)) >> > return -EINVAL; >> > >> > - cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc); >> > + cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps->magic_etc); >> > >> > + rootkuid = make_kuid(fs_ns, 0); >> > switch (magic_etc & VFS_CAP_REVISION_MASK) { >> > case VFS_CAP_REVISION_1: >> > if (size != XATTR_CAPS_SZ_1) >> > @@ -416,15 +594,27 @@ int get_vfs_caps_from_disk(const struct dentry >> > *dentry, struct cpu_vfs_cap_data >> > return -EINVAL; >> > tocopy = VFS_CAP_U32_2; >> > break; >> > + case VFS_CAP_REVISION_3: >> > + if (size != XATTR_CAPS_SZ_3) >> > + return -EINVAL; >> > + tocopy = VFS_CAP_U32_3; >> > + rootkuid = make_kuid(fs_ns, le32_to_cpu(nscaps->rootid)); >> > + break; >> > + >> > default: >> > return -EINVAL; >> > } >> > + /* Limit the caps to the mounter of the filesystem >> > + * or the more limited uid specified in the xattr. >> > + */ >> > + if (!rootid_owns_currentns(rootkuid)) >> > + return -ENODATA; >> > >> > CAP_FOR_EACH_U32(i) { >> > if (i >= tocopy) >> > break; >> > - cpu_caps->permitted.cap[i] = >> > le32_to_cpu(caps.data[i].permitted); >> > - cpu_caps->inheritable.cap[i] = >> > le32_to_cpu(caps.data[i].inheritable); >> > + cpu_caps->permitted.cap[i] = >> > le32_to_cpu(caps->data[i].permitted); >> > + cpu_caps->inheritable.cap[i] = >> > le32_to_cpu(caps->data[i].inheritable); >> > } >> > >> > cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; >> > @@ -462,8 +652,8 @@ static int get_file_caps(struct linux_binprm *bprm, >> > bool *effective, bool *has_c >> > rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); >> > if (rc < 0) { >> > if (rc == -EINVAL) >> > - printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned >> > %d for %s\n", >> > - __func__, rc, bprm->filename); >> > + printk(KERN_NOTICE "Invalid argument reading file caps >> > for %s\n", >> > + bprm->filename); >> > else if (rc == -ENODATA) >> > rc = 0; >> > goto out; >> > @@ -660,15 +850,16 @@ int cap_bprm_secureexec(struct linux_binprm *bprm) >> > int cap_inode_setxattr(struct dentry *dentry, const char *name, >> > const void *value, size_t size, int flags) >> > { >> > - if (!strcmp(name, XATTR_NAME_CAPS)) { >> > - if (!capable(CAP_SETFCAP)) >> > - return -EPERM; >> > + /* Ignore non-security xattrs */ >> > + if (strncmp(name, XATTR_SECURITY_PREFIX, >> > + sizeof(XATTR_SECURITY_PREFIX) - 1) != 0) >> > + return 0; >> > + >> > + // For XATTR_NAME_CAPS the check will be done in __vfs_setxattr_noperm() >> > + if (strcmp(name, XATTR_NAME_CAPS) == 0) >> > return 0; >> > - } >> > >> > - if (!strncmp(name, XATTR_SECURITY_PREFIX, >> > - sizeof(XATTR_SECURITY_PREFIX) - 1) && >> > - !capable(CAP_SYS_ADMIN)) >> > + if (!capable(CAP_SYS_ADMIN)) >> > return -EPERM; >> > return 0; >> > } >> > @@ -686,15 +877,22 @@ int cap_inode_setxattr(struct dentry *dentry, const >> > char *name, >> > */ >> > int cap_inode_removexattr(struct dentry *dentry, const char *name) >> > { >> > - if (!strcmp(name, XATTR_NAME_CAPS)) { >> > - if (!capable(CAP_SETFCAP)) >> > + /* Ignore non-security xattrs */ >> > + if (strncmp(name, XATTR_SECURITY_PREFIX, >> > + sizeof(XATTR_SECURITY_PREFIX) - 1) != 0) >> > + return 0; >> > + >> > + if (strcmp(name, XATTR_NAME_CAPS) == 0) { >> > + /* security.capability gets namespaced */ >> > + struct inode *inode = d_backing_inode(dentry); >> > + if (!inode) >> > + return -EINVAL; >> > + if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP)) >> > return -EPERM; >> > return 0; >> > } >> > >> > - if (!strncmp(name, XATTR_SECURITY_PREFIX, >> > - sizeof(XATTR_SECURITY_PREFIX) - 1) && >> > - !capable(CAP_SYS_ADMIN)) >> > + if (!capable(CAP_SYS_ADMIN)) >> > return -EPERM; >> > return 0; >> > } >> > @@ -1082,6 +1280,7 @@ struct security_hook_list capability_hooks[] = { >> > LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec), >> > LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), >> > LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), >> > + LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity), >> > LSM_HOOK_INIT(mmap_addr, cap_mmap_addr), >> > LSM_HOOK_INIT(mmap_file, cap_mmap_file), >> > LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid),
