EVM: add comment describing why ino field is still unsigned long

Mimi pointed out that we didn't widen the inode number field in struct
h_misc alongside the inode->i_ino widening. While we could make an
equivalent change there, that would require EVM resigning on all 32-bit
hosts.

Instead, leave the field as an unsigned long. This should have no effect
on 64-bit hosts, and allow things to continue working on 32-bit hosts in
the cases where the i_ino fits in 32-bits.

Add a comment explaining why it's being left as unsigned long.

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260316-iino-u64-v3-1-d1076b8f7a20@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index c0ca4eedb0fe5d5c30f45f515a4bc90248ec64ea..1c41af2f91a60a714878ff93b554c90e45546503 100644 (file)
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -144,6 +144,12 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
                          char type, char *digest)
 {
        struct h_misc {
+               /*
+                * Although inode->i_ino is now u64, this field remains
+                * unsigned long to allow existing HMAC and signatures from
+                * 32-bit hosts to continue working when i_ino hasn't changed
+                * and fits in a u32.
+                */
                unsigned long ino;
                __u32 generation;
                uid_t uid;