[PATCH v2] Fix WARNING in __ext4_ioctl

[Pei Li <peili.dev@gmail.com>]

Specify the size of s_volume_name in strscpy_pad() to avoid buffer
overflow.

strscpy_pad() by default takes the size of destination string as the
size to be read from source string. However, as s_volume_name is only
declared as an array of size EXT4_LABEL_MAX, we are reading 1 byte more
than expected.

Reported-by: syzbot+2cab87506a0e7885f4b9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2cab87506a0e7885f4b9
Fixes: 744a56389f73 ("ext4: replace deprecated strncpy with alternatives")
Signed-off-by: Pei Li <peili.dev@gmail.com>
---
strscpy_pad() by default takes the size of destination string as the
size to be read from source string. However, as s_volume_name is only
declared as an array of size EXT4_LABEL_MAX, we are reading 1 byte more
than expected.

Specify the size of s_volume_name in strscpy_pad() to avoid buffer
overflow.
---
Changes in v2:
- Add fixes label
- Move workaround into commit log
- Link to v1: https://lore.kernel.org/r/20240628-bug8-v1-1-417ef53cca33@gmail.com
---
 fs/ext4/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index dab7acd49709..0c4fb579757a 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1151,7 +1151,7 @@ static int ext4_ioctl_getlabel(struct ext4_sb_info *sbi, char __user *user_label
 	BUILD_BUG_ON(EXT4_LABEL_MAX >= FSLABEL_MAX);
 
 	lock_buffer(sbi->s_sbh);
-	strscpy_pad(label, sbi->s_es->s_volume_name);
+	strscpy_pad(label, sbi->s_es->s_volume_name, EXT4_LABEL_MAX);
 	unlock_buffer(sbi->s_sbh);
 
 	if (copy_to_user(user_label, label, sizeof(label)))

---
base-commit: 55027e689933ba2e64f3d245fb1ff185b3e7fc81
change-id: 20240628-bug8-7f700a228c4a

Best regards,
-- 
Pei Li <peili.dev@gmail.com>