lsm: consolidate buffer size handling into lsm_fill_user_ctx()

While we have a lsm_fill_user_ctx() helper function designed to make
life easier for LSMs which return lsm_ctx structs to userspace, we
didn't include all of the buffer length safety checks and buffer
padding adjustments in the helper.  This led to code duplication
across the different LSMs and the possibility for mistakes across the
different LSM subsystems.  In order to reduce code duplication and
decrease the chances of silly mistakes, we're consolidating all of
this code into the lsm_fill_user_ctx() helper.

The buffer padding is also modified from a fixed 8-byte alignment to
an alignment that matches the word length of the machine
(BITS_PER_LONG / 8).

Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index 334f75aa7289..750130a7b9dd 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -492,8 +492,8 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
 int security_locked_down(enum lockdown_reason what);
-int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
-		      size_t context_size, u64 id, u64 flags);
+int lsm_fill_user_ctx(struct lsm_ctx __user *uctx, size_t *uctx_len,
+		      void *val, size_t val_len, u64 id, u64 flags);
 #else /* CONFIG_SECURITY */
 
 static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
@@ -1424,8 +1424,9 @@ static inline int security_locked_down(enum lockdown_reason what)
 {
 	return 0;
 }
-static inline int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
-				    size_t context_size, u64 id, u64 flags)
+static inline int lsm_fill_user_ctx(struct lsm_ctx __user *uctx,
+				    size_t *uctx_len, void *val, size_t val_len,
+				    u64 id, u64 flags)
 {
 	return -EOPNOTSUPP;
 }