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authorJann Horn <jannh@google.com>2016-06-01 11:55:05 +0200
committerSasha Levin <sasha.levin@oracle.com>2016-06-18 16:47:32 -0400
commitc96e6bf5705254a4c93ca25d6d3c68a04fc7ab5b (patch)
tree3615c0d25f6650649b5c05e2524bb8aab262c2d2
parente90b6fdf60b1e5b292c0b8a4eacc862da97e46fc (diff)
proc: prevent stacking filesystems on top
[ Upstream commit e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9 ] This prevents stacking filesystems (ecryptfs and overlayfs) from using procfs as lower filesystem. There is too much magic going on inside procfs, and there is no good reason to stack stuff on top of procfs. (For example, procfs does access checks in VFS open handlers, and ecryptfs by design calls open handlers from a kernel thread that doesn't drop privileges or so.) Signed-off-by: Jann Horn <jannh@google.com> Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
-rw-r--r--fs/proc/root.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 68feb0f70e63..c3e1bc595e6d 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -121,6 +121,13 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
if (IS_ERR(sb))
return ERR_CAST(sb);
+ /*
+ * procfs isn't actually a stacking filesystem; however, there is
+ * too much magic going on inside it to permit stacking things on
+ * top of it
+ */
+ sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
+
if (!proc_parse_options(options, ns)) {
deactivate_locked_super(sb);
return ERR_PTR(-EINVAL);