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From: Jeongjun Park <aha310510@gmail.com>
To: konishi.ryusuke@gmail.com
Cc: linux-nilfs@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	syzbot+2e22057de05b9f3b30d8@syzkaller.appspotmail.com,
	Jeongjun Park <aha310510@gmail.com>
Subject: [PATCH] nilfs: Fix OOB in nilfs_set_de_type
Date: Tue, 16 Apr 2024 00:40:02 +0900
Message-Id: <20240415154002.151149-1-aha310510@gmail.com>
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static void nilfs_set_de_type(struct nilfs_dir_entry *de, struct inode *inode)
{
	umode_t mode = inode->i_mode;

	de->file_type = nilfs_type_by_mode[(mode & S_IFMT)>>S_SHIFT]; // oob
}


The size of the nilfs_type_by_mode array in the fs/nilfs2/dir.c file is defined 
as "S_IFMT >> S_SHIFT", but the nilfs_set_de_type() function, which uses this array, 
specifies the index to read from the array in the same way as "(mode & S_IFMT) >> S_SHIFT".

However, when the index is determined this way, an out-of-bounds (OOB) error occurs by referring 
to an index that is 1 larger than the array size when the condition "mode & S_IFMT == S_IFMT" is satisfied. 
Therefore, a patch to resize the nilfs_type_by_mode array should be applied to prevent OOB errors.


Reported-and-tested-by: syzbot+2e22057de05b9f3b30d8@syzkaller.appspotmail.com
Fixes: 2ba466d74ed7 ("nilfs2: directory entry operations")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 fs/nilfs2/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nilfs2/dir.c b/fs/nilfs2/dir.c
index bc846b904b68..aee40db7a036 100644
--- a/fs/nilfs2/dir.c
+++ b/fs/nilfs2/dir.c
@@ -240,7 +240,7 @@ nilfs_filetype_table[NILFS_FT_MAX] = {
 
 #define S_SHIFT 12
 static unsigned char
-nilfs_type_by_mode[S_IFMT >> S_SHIFT] = {
+nilfs_type_by_mode[(S_IFMT >> S_SHIFT) + 1] = {
        [S_IFREG >> S_SHIFT]    = NILFS_FT_REG_FILE,
        [S_IFDIR >> S_SHIFT]    = NILFS_FT_DIR,
        [S_IFCHR >> S_SHIFT]    = NILFS_FT_CHRDEV,