Fix WARNING in __ext4_ioctl

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.

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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.
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Changes in v2:
- Add fixes label
- Move workaround into commit log
- Link to v1: https://lore.kernel.org/r/[email protected]

---
 fs/ext4/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index dab7acd49709..0c4fb579757a 100644
@@ -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 <[email protected]>

Thanks for the fix, it looks good to me.

Thanks for the patch; however, the correct fix submitted by Kees with this commit:

commit be27cd64461c45a6088a91a04eba5cd44e1767ef

Author: Kees Cook <[email protected]>
Date:   Thu May 23 15:54:12 2024 -0700

ext4: use memtostr_pad() for s_volume_name

As with the other strings in struct ext4_super_block, s_volume_name is not NUL terminated. The other strings were marked in commit 072ebb3bffe6 ("ext4: add nonstring annotations to ext4.h"). Using strscpy() isn't the right replacement for strncpy(); it should use memtostr_pad() instead.

- Ted