The patch titled
Subject: procfs: change the owner of non-dumpable and writeable files
has been added to the -mm tree. Its filename is
procfs-change-the-owner-of-non-dumpable-and-writeable-files.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/procfs-change-the-owner-of-non-dumpable-and-writeable-files.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/procfs-change-the-owner-of-non-dumpable-and-writeable-files.patch
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------------------------------------------------------
From: Aleksa Sarai <asarai@xxxxxxx>
Subject: procfs: change the owner of non-dumpable and writeable files
In order to protect against ptrace(2) and similar attacks on container
runtimes when they join namespaces, many runtimes set mm->dumpable to
SUID_DUMP_DISABLE. However, doing this means that attempting to set up an
unprivileged user namespace will fail because an unprivileged process can
no longer access /proc/self/{setgroups,{uid,gid}_map} for the container
process (which is the same uid as the runtime process).
Fix this by changing pid_getattr to *also* change the owner of regular
files that have a mode of 0644 (when the process is not dumpable). This
ensures that the important /proc/[pid]/... files mentioned above are
properly accessible by a container runtime in a rootless container
context.
The most blantant issue is that a non-dumpable process in a rootless
container context is unable to open /proc/self/setgroups, because it
doesn't own the file.
int main(void)
{
prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
unshare(CLONE_NEWUSER);
/* This will fail. */
int fd = open("/proc/self/setgroups", O_WRONLY);
if (fd < 0)
abort();
return 0;
}
Link: http://lkml.kernel.org/r/20170118040159.4751-1-asarai@xxxxxxx
Signed-off-by: Aleksa Sarai <asarai@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Mateusz Guzik <mguzik@xxxxxxxxxx>
Cc: Janis Danisevskis <jdanis@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN fs/proc/base.c~procfs-change-the-owner-of-non-dumpable-and-writeable-files fs/proc/base.c
--- a/fs/proc/base.c~procfs-change-the-owner-of-non-dumpable-and-writeable-files
+++ a/fs/proc/base.c
@@ -1702,6 +1702,7 @@ int pid_getattr(struct vfsmount *mnt, st
return -ENOENT;
}
if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
+ (inode->i_mode == (S_IFREG|S_IRUGO|S_IWUSR)) ||
task_dumpable(task)) {
cred = __task_cred(task);
stat->uid = cred->euid;
@@ -1743,6 +1744,7 @@ int pid_revalidate(struct dentry *dentry
if (task) {
if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
+ (inode->i_mode == (S_IFREG|S_IRUGO|S_IWUSR)) ||
task_dumpable(task)) {
rcu_read_lock();
cred = __task_cred(task);
@@ -2362,7 +2364,7 @@ out:
return -ENOENT;
}
-static struct dentry *proc_pident_lookup(struct inode *dir,
+static struct dentry *proc_pident_lookup(struct inode *dir,
struct dentry *dentry,
const struct pid_entry *ents,
unsigned int nents)
@@ -2504,7 +2506,7 @@ static const struct pid_entry attr_dir_s
static int proc_attr_dir_readdir(struct file *file, struct dir_context *ctx)
{
- return proc_pident_readdir(file, ctx,
+ return proc_pident_readdir(file, ctx,
attr_dir_stuff, ARRAY_SIZE(attr_dir_stuff));
}
_
Patches currently in -mm which might be from asarai@xxxxxxx are
procfs-change-the-owner-of-non-dumpable-and-writeable-files.patch
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