diff mbox series

[RESEND,v6,3/5] proc: Disable cancellation of subset=pid option

Message ID 883677463902534d2de724dca9ff139f6ad777b8.1626432185.git.legion@kernel.org (mailing list archive)
State New, archived
Headers show
Series proc: subset=pid: Relax check of mount visibility | expand

Commit Message

Alexey Gladkov July 16, 2021, 10:46 a.m. UTC 
When procfs is mounted with subset=pid option, where is no way to
remount it with this option removed. This is done in order not to make
visible what ever was hidden since some checks occur during mount.

This patch makes the limitation explicit and prints an error message.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
 fs/proc/root.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 6a75ac717455..0d20bb67e79a 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -145,7 +145,7 @@  static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	return 0;
 }
 
-static void proc_apply_options(struct proc_fs_info *fs_info,
+static int proc_apply_options(struct proc_fs_info *fs_info,
 			       struct fs_context *fc,
 			       struct user_namespace *user_ns)
 {
@@ -155,8 +155,12 @@  static void proc_apply_options(struct proc_fs_info *fs_info,
 		fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
 	if (ctx->mask & (1 << Opt_hidepid))
 		fs_info->hide_pid = ctx->hidepid;
-	if (ctx->mask & (1 << Opt_subset))
+	if (ctx->mask & (1 << Opt_subset)) {
+		if (ctx->pidonly != PROC_PIDONLY_ON && fs_info->pidonly == PROC_PIDONLY_ON)
+			return invalf(fc, "proc: subset=pid cannot be unset\n");
 		fs_info->pidonly = ctx->pidonly;
+	}
+	return 0;
 }
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)
@@ -172,7 +176,9 @@  static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 
 	fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
 	fs_info->mounter_cred = get_cred(fc->cred);
-	proc_apply_options(fs_info, fc, current_user_ns());
+	ret = proc_apply_options(fs_info, fc, current_user_ns());
+	if (ret)
+		return ret;
 
 	/* User space would break if executables or devices appear on proc */
 	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
@@ -224,8 +230,7 @@  static int proc_reconfigure(struct fs_context *fc)
 	put_cred(fs_info->mounter_cred);
 	fs_info->mounter_cred = get_cred(fc->cred);
 
-	proc_apply_options(fs_info, fc, current_user_ns());
-	return 0;
+	return proc_apply_options(fs_info, fc, current_user_ns());
 }
 
 static int proc_get_tree(struct fs_context *fc)