The internal function inode_capable was used inappropriately. Depending on configuration, this may be usable to escalate privileges. A cursory inspection of my Fedora box suggests that it is not vulnerable to the obvious way to exploit this bug. The fix should appear in Linus' -master shortly, and it's tagged for stable. In the mean time, I've attached it here. I'll follow up in a day or two with a description of the actual bug, or one of you can try to beat me to it. From fc8ad6759de122ee180a02c16518c2e252cc9d48 Mon Sep 17 00:00:00 2001 Message-Id: <fc8ad6759de122ee180a02c16518c2e252cc9d48.1402429263.git.luto () amacapital net> From: Andy Lutomirski <luto () amacapital net> Date: Tue, 10 Jun 2014 12:35:26 -0700 Subject: [PATCH v3] fs,userns: Change inode_capable to capable_wrt_inode_uidgid The kernel has no concept of capabilities with respect to inodes; inodes exist independently of namespaces. For example, inode_capable(inode, CAP_LINUX_IMMUTABLE) would be nonsense. This patch changes inode_capable to check for uid and gid mappings and renames it to capable_wrt_inode_uidgid, which should make it more obvious what it does. Fixes CVE-2014-4014. Cc: Theodore Ts'o <tytso () mit edu> Cc: Serge Hallyn <serge.hallyn () ubuntu com> Cc: "Eric W. Biederman" <ebiederm () xmission com> Cc: Dave Chinner <david () fromorbit com> Cc: stable () vger kernel org Signed-off-by: Andy Lutomirski <luto () amacapital net> --- fs/attr.c | 8 ++++---- fs/inode.c | 10 +++++++--- fs/namei.c | 11 ++++++----- fs/xfs/xfs_ioctl.c | 2 +- include/linux/capability.h | 2 +- kernel/capability.c | 20 ++++++++------------ 6 files changed, 27 insertions(+), 26 deletions(-) diff --git a/fs/attr.c b/fs/attr.c index 5d4e59d..6530ced 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -50,14 +50,14 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr) if ((ia_valid & ATTR_UID) && (!uid_eq(current_fsuid(), inode->i_uid) || !uid_eq(attr->ia_uid, inode->i_uid)) && - !inode_capable(inode, CAP_CHOWN)) + !capable_wrt_inode_uidgid(inode, CAP_CHOWN)) return -EPERM; /* Make sure caller can chgrp. */ if ((ia_valid & ATTR_GID) && (!uid_eq(current_fsuid(), inode->i_uid) || (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) && - !inode_capable(inode, CAP_CHOWN)) + !capable_wrt_inode_uidgid(inode, CAP_CHOWN)) return -EPERM; /* Make sure a caller can chmod. */ @@ -67,7 +67,7 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr) /* Also check the setgid bit! */ if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid : inode->i_gid) && - !inode_capable(inode, CAP_FSETID)) + !capable_wrt_inode_uidgid(inode, CAP_FSETID)) attr->ia_mode &= ~S_ISGID; } @@ -160,7 +160,7 @@ void setattr_copy(struct inode *inode, const struct iattr *attr) umode_t mode = attr->ia_mode; if (!in_group_p(inode->i_gid) && - !inode_capable(inode, CAP_FSETID)) + !capable_wrt_inode_uidgid(inode, CAP_FSETID)) mode &= ~S_ISGID; inode->i_mode = mode; } diff --git a/fs/inode.c b/fs/inode.c index f96d2a6..d2fb2f2 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1839,14 +1839,18 @@ EXPORT_SYMBOL(inode_init_owner); * inode_owner_or_capable - check current task permissions to inode * @inode: inode being checked * - * Return true if current either has CAP_FOWNER to the inode, or - * owns the file. + * Return true if current either has CAP_FOWNER in a namespace with the + * inode owner uid mapped, or owns the file. */ bool inode_owner_or_capable(const struct inode *inode) { + struct user_namespace *ns; + if (uid_eq(current_fsuid(), inode->i_uid)) return true; - if (inode_capable(inode, CAP_FOWNER)) + + ns = current_user_ns(); + if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid)) return true; return false; } diff --git a/fs/namei.c b/fs/namei.c index 8016827..985c6f3 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -332,10 +332,11 @@ int generic_permission(struct inode *inode, int mask) if (S_ISDIR(inode->i_mode)) { /* DACs are overridable for directories */ - if (inode_capable(inode, CAP_DAC_OVERRIDE)) + if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE)) return 0; if (!(mask & MAY_WRITE)) - if (inode_capable(inode, CAP_DAC_READ_SEARCH)) + if (capable_wrt_inode_uidgid(inode, + CAP_DAC_READ_SEARCH)) return 0; return -EACCES; } @@ -345,7 +346,7 @@ int generic_permission(struct inode *inode, int mask) * at least one exec bit set. */ if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO)) - if (inode_capable(inode, CAP_DAC_OVERRIDE)) + if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE)) return 0; /* @@ -353,7 +354,7 @@ int generic_permission(struct inode *inode, int mask) */ mask &= MAY_READ | MAY_WRITE | MAY_EXEC; if (mask == MAY_READ) - if (inode_capable(inode, CAP_DAC_READ_SEARCH)) + if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH)) return 0; return -EACCES; @@ -2379,7 +2380,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode) return 0; if (uid_eq(dir->i_uid, fsuid)) return 0; - return !inode_capable(inode, CAP_FOWNER); + return !capable_wrt_inode_uidgid(inode, CAP_FOWNER); } /* diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c index 0b18776..6152cbe 100644 --- a/fs/xfs/xfs_ioctl.c +++ b/fs/xfs/xfs_ioctl.c @@ -1215,7 +1215,7 @@ xfs_ioctl_setattr( * cleared upon successful return from chown() */ if ((ip->i_d.di_mode & (S_ISUID|S_ISGID)) && - !inode_capable(VFS_I(ip), CAP_FSETID)) + !capable_wrt_inode_uidgid(VFS_I(ip), CAP_FSETID)) ip->i_d.di_mode &= ~(S_ISUID|S_ISGID); /* diff --git a/include/linux/capability.h b/include/linux/capability.h index a6ee1f9..84b13ad 100644 --- a/include/linux/capability.h +++ b/include/linux/capability.h @@ -210,7 +210,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t, struct user_namespace *ns, int cap); extern bool capable(int cap); extern bool ns_capable(struct user_namespace *ns, int cap); -extern bool inode_capable(const struct inode *inode, int cap); +extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap); extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap); /* audit system wants to get cap info from files as well */ diff --git a/kernel/capability.c b/kernel/capability.c index a8d63df..24663b3 100644 --- a/kernel/capability.c +++ b/kernel/capability.c @@ -424,23 +424,19 @@ bool capable(int cap) EXPORT_SYMBOL(capable); /** - * inode_capable - Check superior capability over inode + * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped * @inode: The inode in question * @cap: The capability in question * - * Return true if the current task has the given superior capability - * targeted at it's own user namespace and that the given inode is owned - * by the current user namespace or a child namespace. - * - * Currently we check to see if an inode is owned by the current - * user namespace by seeing if the inode's owner maps into the - * current user namespace. - * + * Return true if the current task has the given capability targeted at + * its own user namespace and that the given inode's uid and gid are + * mapped into the current user namespace. */ -bool inode_capable(const struct inode *inode, int cap) +bool capable_wrt_inode_uidgid(const struct inode *inode, int cap) { struct user_namespace *ns = current_user_ns(); - return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid); + return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) && + kgid_has_mapping(ns, inode->i_gid); } -EXPORT_SYMBOL(inode_capable); +EXPORT_SYMBOL(capable_wrt_inode_uidgid); -- 1.9.3