From b6c65324836b91bfa3bbd8b4b9db2f0109216b44 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Mon, 29 Jun 2015 14:42:03 -0500 Subject: [PATCH] vfs: Commit to never having exectuables on proc and sysfs. Today proc and sysfs do not contain any executable files. Several applications today mount proc or sysfs without noexec and nosuid and then depend on there being no exectuables files on proc or sysfs. Having any executable files show on proc or sysfs would cause a user space visible regression, and most likely security problems. Therefore commit to never allowing executables on proc and sysfs by adding a new flag to mark them as filesystems without executables and enforce that flag. Test the flag where MNT_NOEXEC is tested today, so that the only user visible effect will be that exectuables will be treated as if the execute bit is cleared. The filesystems proc and sysfs do not currently incoporate any executable files so this does not result in any user visible effects. This makes it unnecessary to vet changes to proc and sysfs tightly for adding exectuable files or changes to chattr that would modify existing files, as no matter what the individual file say they will not be treated as exectuable files by the vfs. Not having to vet changes to closely is important as without this we are only one proc_create call (or another goof up in the implementation of notify_change) from having problematic executables on proc. Those mistakes are all too easy to make and would create a situation where there are security issues or the assumptions of some program having to be broken (and cause userspace regressions). Signed-off-by: "Eric W. Biederman" (cherry picked from commit 90f8572b0f021fdd1baa68e00a8c30482ee9e5f4) Orabug: 26540416 CVE: CVE-2016-10044 Signed-off-by: Tim Tianyang Chen Reviewed-by: Jack Vogel Conflicts: include/linux/fs.h --- fs/exec.c | 10 ++++++++-- fs/open.c | 2 +- fs/proc/root.c | 2 ++ fs/sysfs/mount.c | 4 ++++ include/linux/fs.h | 3 +++ kernel/sys.c | 3 +-- mm/mmap.c | 4 ++-- mm/nommu.c | 2 +- security/security.c | 2 +- 9 files changed, 23 insertions(+), 9 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 133202e0fa2f..9139f5a3c545 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -100,6 +100,12 @@ static inline void put_binfmt(struct linux_binfmt * fmt) module_put(fmt->module); } +bool path_noexec(const struct path *path) +{ + return (path->mnt->mnt_flags & MNT_NOEXEC) || + (path->mnt->mnt_sb->s_iflags & SB_I_NOEXEC); +} + #ifdef CONFIG_USELIB /* * Note that a shared library must be both readable and executable due to @@ -134,7 +140,7 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) goto exit; error = -EACCES; - if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) + if (path_noexec(&file->f_path)) goto exit; fsnotify_open(file); @@ -799,7 +805,7 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) if (!S_ISREG(file_inode(file)->i_mode)) goto exit; - if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) + if (path_noexec(&file->f_path)) goto exit; err = deny_write_access(file); diff --git a/fs/open.c b/fs/open.c index 7bab5a4bb7b0..72435c2b460f 100644 --- a/fs/open.c +++ b/fs/open.c @@ -377,7 +377,7 @@ retry: * with the "noexec" flag. */ res = -EACCES; - if (path.mnt->mnt_flags & MNT_NOEXEC) + if (path_noexec(&path)) goto out_path_release; } diff --git a/fs/proc/root.c b/fs/proc/root.c index c3e1bc595e6d..ec649c92d270 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -141,6 +141,8 @@ static struct dentry *proc_mount(struct file_system_type *fs_type, } sb->s_flags |= MS_ACTIVE; + /* User space would break if executables appear on proc */ + sb->s_iflags |= SB_I_NOEXEC; } return dget(sb->s_root); diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c index 1c6ac6fcee9f..f3db82071cfb 100644 --- a/fs/sysfs/mount.c +++ b/fs/sysfs/mount.c @@ -40,6 +40,10 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type, SYSFS_MAGIC, &new_sb, ns); if (IS_ERR(root) || !new_sb) kobj_ns_drop(KOBJ_NS_TYPE_NET, ns); + else if (new_sb) + /* Userspace would break if executables appear on sysfs */ + root->d_sb->s_iflags |= SB_I_NOEXEC; + return root; } diff --git a/include/linux/fs.h b/include/linux/fs.h index 1c57d74c1372..f8fd2cdbd6fd 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1253,6 +1253,8 @@ struct mm_struct; #define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */ #define UMOUNT_UNUSED 0x80000000 /* Flag guaranteed to be unused */ +/* sb->s_iflags */ +#define SB_I_NOEXEC 0x00000002 /* Ignore executables on this fs */ /* Possible states of 'frozen' field */ enum { @@ -3005,4 +3007,5 @@ static inline bool dir_relax(struct inode *inode) return !IS_DEADDIR(inode); } +extern bool path_noexec(const struct path *path); #endif /* _LINUX_FS_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 25ae8d2e65e2..62f596a0d83d 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1668,8 +1668,7 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) * overall picture. */ err = -EACCES; - if (!S_ISREG(inode->i_mode) || - exe.file->f_path.mnt->mnt_flags & MNT_NOEXEC) + if (!S_ISREG(inode->i_mode) || path_noexec(&exe.file->f_path)) goto exit; err = inode_permission(inode, MAY_EXEC); diff --git a/mm/mmap.c b/mm/mmap.c index 33d2142b9bf7..4c07adafa01b 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1326,7 +1326,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr, * mounted, in which case we dont add PROT_EXEC.) */ if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC)) - if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC))) + if (!(file && path_noexec(&file->f_path))) prot |= PROT_EXEC; if (!len) @@ -1398,7 +1398,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr, case MAP_PRIVATE: if (!(file->f_mode & FMODE_READ)) return -EACCES; - if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) { + if (path_noexec(&file->f_path)) { if (vm_flags & VM_EXEC) return -EPERM; vm_flags &= ~VM_MAYEXEC; diff --git a/mm/nommu.c b/mm/nommu.c index cc5fe1804a99..19a7bdedd230 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1074,7 +1074,7 @@ static int validate_mmap_request(struct file *file, /* handle executable mappings and implied executable * mappings */ - if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) { + if (path_noexec(&file->f_path)) { if (prot & PROT_EXEC) return -EPERM; } else if ((prot & PROT_READ) && !(prot & PROT_EXEC)) { diff --git a/security/security.c b/security/security.c index 8e9b1f4b9b45..391496b0c877 100644 --- a/security/security.c +++ b/security/security.c @@ -751,7 +751,7 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot) * ditto if it's not on noexec mount, except that on !MMU we need * NOMMU_MAP_EXEC (== VM_MAYEXEC) in this case */ - if (!(file->f_path.mnt->mnt_flags & MNT_NOEXEC)) { + if (!path_noexec(&file->f_path)) { #ifndef CONFIG_MMU if (file->f_op->mmap_capabilities) { unsigned caps = file->f_op->mmap_capabilities(file); -- 2.50.1