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authorEric W. Biederman <ebiederm@xmission.com>2015-06-29 14:42:03 -0500
committerEric W. Biederman <ebiederm@xmission.com>2015-07-10 10:39:25 -0500
commit90f8572b0f021fdd1baa68e00a8c30482ee9e5f4 (patch)
tree10d9f60b58c70411c72f537457853d03afd5a56a /fs
parentd770e558e21961ad6cfdf0ff7df0eb5d7d4f0754 (diff)
downloadlinux-0-day-90f8572b0f021fdd1baa68e00a8c30482ee9e5f4.tar.gz
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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" <ebiederm@xmission.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c10
-rw-r--r--fs/open.c2
-rw-r--r--fs/proc/root.c2
-rw-r--r--fs/sysfs/mount.c4
4 files changed, 15 insertions, 3 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 1977c2a553aca..b06623a9347f4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -98,6 +98,12 @@ 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
@@ -132,7 +138,7 @@ 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);
@@ -777,7 +783,7 @@ 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 e33dab287fa00..b6f1e96a7c0b3 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 68feb0f70e635..361ab4ee42fc3 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -134,6 +134,8 @@ 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 1c6ac6fcee9fb..f3db82071cfbd 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;
}