Add the __counted_by compiler attribute to the flexible array member
a_entries to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Use struct_size() to calculate the number of bytes to allocate for new
and cloned acls and remove the local size variables.

Change the posix_acl_alloc() function parameter count from int to
unsigned int to match posix_acl's a_count data type. Add identifier
names to the function definition to silence two checkpatch warnings.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Cc: Nathan Chancellor <nathan@kernel.org>
---
Changes in v2:
- Update patch to apply cleanly to linux-next. With 8f0a7a2d7bc3
  ("acl: Realign struct posix_acl to save 8 bytes") in -next, this
  patch should not trigger the false-positive buffer overflow anymore
- Link to v1: https://lore.kernel.org/linux-kernel/20240923213809.235128-2-thorsten.blum@linux.dev/
---
 fs/posix_acl.c            | 13 ++++++-------
 include/linux/posix_acl.h |  4 ++--
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 6c66a37522d0..4050942ab52f 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -200,11 +200,11 @@ EXPORT_SYMBOL(posix_acl_init);
  * Allocate a new ACL with the specified number of entries.
  */
 struct posix_acl *
-posix_acl_alloc(int count, gfp_t flags)
+posix_acl_alloc(unsigned int count, gfp_t flags)
 {
-	const size_t size = sizeof(struct posix_acl) +
-	                    count * sizeof(struct posix_acl_entry);
-	struct posix_acl *acl = kmalloc(size, flags);
+	struct posix_acl *acl;
+
+	acl = kmalloc(struct_size(acl, a_entries, count), flags);
 	if (acl)
 		posix_acl_init(acl, count);
 	return acl;
@@ -220,9 +220,8 @@ posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
 	struct posix_acl *clone = NULL;
 
 	if (acl) {
-		int size = sizeof(struct posix_acl) + acl->a_count *
-		           sizeof(struct posix_acl_entry);
-		clone = kmemdup(acl, size, flags);
+		clone = kmemdup(acl, struct_size(acl, a_entries, acl->a_count),
+				flags);
 		if (clone)
 			refcount_set(&clone->a_refcount, 1);
 	}
diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index 2d6a4badd306..e2d47eb1a7f3 100644
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -30,7 +30,7 @@ struct posix_acl {
 	refcount_t		a_refcount;
 	unsigned int		a_count;
 	struct rcu_head		a_rcu;
-	struct posix_acl_entry	a_entries[];
+	struct posix_acl_entry	a_entries[] __counted_by(a_count);
 };
 
 #define FOREACH_ACL_ENTRY(pa, acl, pe) \
@@ -62,7 +62,7 @@ posix_acl_release(struct posix_acl *acl)
 /* posix_acl.c */
 
 extern void posix_acl_init(struct posix_acl *, int);
-extern struct posix_acl *posix_acl_alloc(int, gfp_t);
+extern struct posix_acl *posix_acl_alloc(unsigned int count, gfp_t flags);
 extern struct posix_acl *posix_acl_from_mode(umode_t, gfp_t);
 extern int posix_acl_equiv_mode(const struct posix_acl *, umode_t *);
 extern int __posix_acl_create(struct posix_acl **, gfp_t, umode_t *);
-- 
2.47.0

On Fri, 18 Oct 2024 14:14:21 +0200, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member
> a_entries to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Use struct_size() to calculate the number of bytes to allocate for new
> and cloned acls and remove the local size variables.
> 
> [...]

Applied to the vfs.misc branch of the vfs/vfs.git tree.
Patches in the vfs.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.misc

[1/1] acl: Annotate struct posix_acl with __counted_by()
      https://git.kernel.org/vfs/vfs/c/ac0812ef00c8