[PATCH v3 2/3] KEYS: Reject @desclen values >= KEY_MAX_DESC_SIZE in key_alloc()

[Jarkko Sakkinen <jarkko@kernel.org>]

@desclen in key_alloc() is saved to the 16-bit wide desc_len field in
struct keyring_index_key.

Reject @desclen values at or above KEY_MAX_DESC_SIZE with -EINVAL in order
to match the userspace limit. The constraints inherits from the one byte
required for the NULL character.

Cc: stable@vger.kernel.org
Assisted-by: LLM
Fixes: f771fde82051 ("keys: Simplify key description management")
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 include/linux/key.h    | 2 ++
 security/keys/key.c    | 2 ++
 security/keys/keyctl.c | 2 --
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 26139c3adf62..fa88de9b5a9b 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -37,6 +37,8 @@ struct net;
 
 #undef KEY_DEBUGGING
 
+#define KEY_MAX_DESC_SIZE 4096
+
 #define KEY_POS_VIEW	0x01000000	/* possessor can view a key's attributes */
 #define KEY_POS_READ	0x02000000	/* possessor can read key payload / view keyring */
 #define KEY_POS_WRITE	0x04000000	/* possessor can update key payload / add link to keyring */
diff --git a/security/keys/key.c b/security/keys/key.c
index 6ebb8691551f..e9f8cacf00c8 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -245,6 +245,8 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 	}
 
 	desclen = strlen(desc);
+	if (desclen >= KEY_MAX_DESC_SIZE)
+		goto error;
 	quotalen = desclen + 1 + type->def_datalen;
 
 	/* get hold of the key tracking for this user */
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 36ffba0ebba6..d6b10fd67627 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -24,8 +24,6 @@
 #include <keys/request_key_auth-type.h>
 #include "internal.h"
 
-#define KEY_MAX_DESC_SIZE 4096
-
 static const unsigned char keyrings_capabilities[2] = {
 	[0] = (KEYCTL_CAPS0_CAPABILITIES |
 	       (IS_ENABLED(CONFIG_PERSISTENT_KEYRINGS)	? KEYCTL_CAPS0_PERSISTENT_KEYRINGS : 0) |
-- 
2.47.3