[PATCH v12 06/12] procfs: switch magic-link modes to be more sane

Aleksa Sarai
2019-09-04T20:19:27Z

Now that magic-link modes are obeyed for file re-opening purposes, some
of the pre-existing magic-link modes need to be adjusted to be more
semantically correct.

The most blatant example of this is /proc/self/exe, which had a mode of
a+rwx even though tautologically the file could never be opened for
writing (because it is the current->mm of a live process).

With the new O_PATH restrictions, changing the default mode of these
magic-links allows us to avoid delayed-access attacks such as we saw in
CVE-2019-5736.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
fs/proc/base.c | 20 ++++++++++----------
fs/proc/namespaces.c | 2 +-
2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..297242174402 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -133,9 +133,9 @@ struct pid_entry {

#define DIR(NAME, MODE, iops, fops) \
NOD(NAME, (S_IFDIR|(MODE)), &iops, &fops, {} )
-#define LNK(NAME, get_link) \
- NOD(NAME, (S_IFLNK|S_IRWXUGO), \
- &proc_pid_link_inode_operations, NULL, \
+#define LNK(NAME, MODE, get_link) \
+ NOD(NAME, (S_IFLNK|(MODE)), \
+ &proc_pid_link_inode_operations, NULL, \
{ .proc_get_link = get_link } )
#define REG(NAME, MODE, fops) \
NOD(NAME, (S_IFREG|(MODE)), NULL, &fops, {})
@@ -3028,9 +3028,9 @@ static const struct pid_entry tgid_base_stuff[] = {
REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations),
#endif
REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations),
- LNK("cwd", proc_cwd_link),
- LNK("root", proc_root_link),
- LNK("exe", proc_exe_link),
+ LNK("cwd", S_IRWXUGO, proc_cwd_link),
+ LNK("root", S_IRWXUGO, proc_root_link),
+ LNK("exe", S_IRUGO|S_IXUGO, proc_exe_link),
REG("mounts", S_IRUGO, proc_mounts_operations),
REG("mountinfo", S_IRUGO, proc_mountinfo_operations),
REG("mountstats", S_IRUSR, proc_mountstats_operations),
@@ -3429,11 +3429,11 @@ static const struct pid_entry tid_base_stuff[] = {
REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations),
#endif
REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations),
- LNK("cwd", proc_cwd_link),
- LNK("root", proc_root_link),
- LNK("exe", proc_exe_link),
+ LNK("cwd", S_IRWXUGO, proc_cwd_link),
+ LNK("root", S_IRWXUGO, proc_root_link),
+ LNK("exe", S_IRUGO|S_IXUGO, proc_exe_link),
REG("mounts", S_IRUGO, proc_mounts_operations),
- REG("mountinfo", S_IRUGO, proc_mountinfo_operations),
+ REG("mountinfo", S_IRUGO, proc_mountinfo_operations),
#ifdef CONFIG_PROC_PAGE_MONITOR
REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
REG("smaps", S_IRUGO, proc_pid_smaps_operations),
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index dd2b35f78b09..cd1e130913f7 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -94,7 +94,7 @@ static struct dentry *proc_ns_instantiate(struct dentry *dentry,
struct inode *inode;
struct proc_inode *ei;

- inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK | S_IRWXUGO);
+ inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK | S_IRUGO);
if (!inode)
return ERR_PTR(-ENOENT);

--
2.23.0