[PATCH 4/5] CVE-2025-26725: fs: jffs2: fix malloc(size + constant) buffer overflow issues

[Sascha Hauer <s.hauer@pengutronix.de>]

The pattern malloc(size + constant) is dangerous when size can be
manipulated by an attacker. In that case 'size' can be manipulated
in a way that 'size + constant' is 0 due to integer overflow. The
result is a zero sized buffer to which is then data written to.

Avoid this by using size_add() and struct_size() instead.

Reported-by: Jonathan Bar Or <jonathanbaror@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 fs/jffs2/malloc.c    | 4 ++--
 fs/jffs2/nodelist.h  | 2 +-
 fs/jffs2/readinode.c | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/jffs2/malloc.c b/fs/jffs2/malloc.c
index e0e29fa648..61c2430c18 100644
--- a/fs/jffs2/malloc.c
+++ b/fs/jffs2/malloc.c
@@ -15,10 +15,10 @@
 #include <linux/jffs2.h>
 #include "nodelist.h"
 
-struct jffs2_full_dirent *jffs2_alloc_full_dirent(int namesize)
+struct jffs2_full_dirent *jffs2_alloc_full_dirent(size_t namesize)
 {
 	struct jffs2_full_dirent *ret;
-	ret = kmalloc(sizeof(*ret) + namesize, GFP_KERNEL);
+	ret = kmalloc(struct_size(ret, name, namesize), GFP_KERNEL);
 	dbg_memalloc("%p\n", ret);
 	return ret;
 }
diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
index d8687319c7..28b35d6d58 100644
--- a/fs/jffs2/nodelist.h
+++ b/fs/jffs2/nodelist.h
@@ -440,7 +440,7 @@ void jffs2_do_clear_inode(struct jffs2_sb_info *c, struct jffs2_inode_info *f);
 
 /* malloc.c */
 
-struct jffs2_full_dirent *jffs2_alloc_full_dirent(int namesize);
+struct jffs2_full_dirent *jffs2_alloc_full_dirent(size_t namesize);
 void jffs2_free_full_dirent(struct jffs2_full_dirent *);
 struct jffs2_full_dnode *jffs2_alloc_full_dnode(void);
 void jffs2_free_full_dnode(struct jffs2_full_dnode *dnode);
diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
index 605130d60c..4634ee5818 100644
--- a/fs/jffs2/readinode.c
+++ b/fs/jffs2/readinode.c
@@ -601,7 +601,7 @@ static inline int read_direntry(struct jffs2_sb_info *c, struct jffs2_raw_node_r
 		spin_unlock(&c->erase_completion_lock);
 	}
 
-	fd = jffs2_alloc_full_dirent(rd->nsize + 1);
+	fd = jffs2_alloc_full_dirent(size_add(rd->nsize, 1));
 	if (unlikely(!fd))
 		return -ENOMEM;
 
-- 
2.39.5