[PATCH 6.1 269/609] proc: Fix broken error paths for namespace links

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <[email protected]>

commit 425224c2d700391729be7fe6929a88ef4e2d7a4e upstream.

Don't return the return value of down_read_killable() (0) when a ptrace
access check fails, return -EACCES as intended.

Reported-by: Magnus Lindholm <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Fixes: 6650527444da ("proc: protect ptrace_may_access() with exec_update_lock (part 1)")
Cc: [email protected]
Signed-off-by: Jann Horn <[email protected]>
Link: https://patch.msgid.link/[email protected]
Tested-by: Magnus Lindholm <[email protected]>
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 fs/proc/namespaces.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -46,7 +46,7 @@ static const char *proc_ns_get_link(stru
 	const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops;
 	struct task_struct *task;
 	struct path ns_path;
-	int error = -EACCES;
+	int error;
 
 	if (!dentry)
 		return ERR_PTR(-ECHILD);
@@ -59,6 +59,7 @@ static const char *proc_ns_get_link(stru
 	if (error)
 		goto out_put_task;
 
+	error = -EACCES;
 	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
 		goto out;
 
@@ -90,6 +91,7 @@ static int proc_ns_readlink(struct dentr
 	if (res)
 		goto out_put_task;
 
+	res = -EACCES;
 	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) {
 		res = ns_get_name(name, sizeof(name), task, ns_ops);
 		if (res >= 0)