[PATCH] keys: translate request_key_auth pid for the reading procfs instance

[PATCH] keys: translate request_key_auth pid for the reading procfs instance

[Maoyi Xie]

request_key_auth_describe() prints rka->pid into /proc/keys as a raw
pid_t in the initial pid namespace. A reader can open /proc/keys through
a mount in another pid namespace. That reader sees a number with no
meaning there. The number can even name an unrelated task. The line
needs VIEW on the key. So the reader either shares the key owner's uid
or possesses the key.

The fix keeps a struct pid. Commit 4f82f45730c6 ("net ip6 flowlabel:
Make owner a union of struct pid * and kuid_t") gave
/proc/net/ip6_flowlabel the same storage. The print goes through
pid_nr_ns(). It renders against the pid namespace of the procfs instance
the line is read through. Commit ad08978ab41c ("ipv6/flowlabel: simplify
pid namespace lookup") moved that print to the same anchor. Output
through an initial namespace /proc does not change. The line shows 0 for
a requestor with no number in that namespace.

Translating at read time was the alternative. find_pid_ns() can resolve
a recycled number. The line would then name a live task with no
connection to the key. A stored struct pid gives 0 instead when the
requestor has no number there.

Link: https://lore.kernel.org/keyrings/20260809110202.2180410-1-maoyixie.tju@gmail.com/
Fixes: 78b7280cce23 ("KEYS: Improve /proc/keys")
Cc: stable@vger.kernel.org # v5.10+
Assisted-by: Claude:claude-opus-5 codeql
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
---

 include/keys/request_key_auth-type.h |  2 +-
 security/keys/request_key_auth.c     | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/include/keys/request_key_auth-type.h b/include/keys/request_key_auth-type.h
index 01e42ee5f4099..464636278c4f8 100644
--- a/include/keys/request_key_auth-type.h
+++ b/include/keys/request_key_auth-type.h
@@ -22,7 +22,7 @@ struct request_key_auth {
 	const struct cred	*cred;
 	void			*callout_info;
 	size_t			callout_len;
-	pid_t			pid;
+	struct pid		*pid;
 	char			op[8];
 } __randomize_layout;
 
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 282e09d8fa46c..ed6f55b9cdd93 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -9,6 +9,8 @@
 
 #include <linux/sched.h>
 #include <linux/err.h>
+#include <linux/pid.h>
+#include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
@@ -73,7 +75,10 @@ static void request_key_auth_describe(const struct key *key,
 	seq_puts(m, "key:");
 	seq_puts(m, key->description);
 	if (key_is_positive(key))
-		seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
+		seq_printf(m, " pid:%d ci:%zu",
+			   pid_nr_ns(rka->pid,
+				     proc_pid_ns(file_inode(m->file)->i_sb)),
+			   rka->callout_len);
 }
 
 /*
@@ -113,6 +118,7 @@ static void free_request_key_auth(struct request_key_auth *rka)
 	if (rka->cred)
 		put_cred(rka->cred);
 	kfree(rka->callout_info);
+	put_pid(rka->pid);
 	kfree(rka);
 }
 
@@ -226,14 +232,14 @@ struct key *request_key_auth_new(struct key *target, const char *op,
 
 		irka = cred->request_key_auth->payload.data[0];
 		rka->cred = get_cred(irka->cred);
-		rka->pid = irka->pid;
+		rka->pid = get_pid(irka->pid);
 
 		up_read(&cred->request_key_auth->sem);
 	}
 	else {
 		/* it isn't - use this process as the context */
 		rka->cred = get_cred(cred);
-		rka->pid = current->pid;
+		rka->pid = get_pid(task_pid(current));
 	}
 
 	rka->target_key = key_get(target);
-- 
2.34.1