linux-kernel - Re: [PATCH] bcachefs: replace deprecated strncpy() with strscpy()

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Message-ID: <wdagx2vwyv7s2t2tcndwmambwdhmoitvhmnzcopdl3xkfq6ct2@evmzpxnuhi4e>
Date: Wed, 26 Mar 2025 10:47:59 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Roxana Nicolescu <nicolescu.roxana@...tonmail.com>
Cc: Alan Huang <mmpgouride@...il.com>, linux-bcachefs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH] bcachefs: replace deprecated strncpy() with strscpy()

On Wed, Mar 26, 2025 at 02:40:22PM +0000, Roxana Nicolescu wrote:
> On Wednesday, March 26th, 2025 at 1:19 PM, Kent Overstreet <kent.overstreet@...ux.dev> wrote:
> 
> > On Wed, Mar 26, 2025 at 06:02:31PM +0800, Alan Huang wrote:
> > 
> > > On Mar 26, 2025, at 17:44, Roxana Nicolescu nicolescu.roxana@...tonmail.com wrote:
> > > 
> > > > strncpy() is deprecated for NUL-terminated destination buffers. Use
> > > > strscpy() instead.
> > > > 
> > > > Link: https://github.com/KSPP/linux/issues/90
> > > > Signed-off-by: Roxana Nicolescu nicolescu.roxana@...tonmail.com
> > > > ---
> > > > fs/bcachefs/btree_trans_commit.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/bcachefs/btree_trans_commit.c b/fs/bcachefs/btree_trans_commit.c
> > > > index c4f524b2ca9a..7ab25b425d11 100644
> > > > --- a/fs/bcachefs/btree_trans_commit.c
> > > > +++ b/fs/bcachefs/btree_trans_commit.c
> > > > @@ -364,7 +364,7 @@ static noinline void journal_transaction_name(struct btree_trans *trans)
> > > > struct jset_entry_log *l =
> > > > container_of(entry, struct jset_entry_log, entry);
> > > > 
> > > > - strncpy(l->d, trans->fn, JSET_ENTRY_LOG_U64s * sizeof(u64));
> > > > + strscpy(l->d, trans->fn, JSET_ENTRY_LOG_U64s * sizeof(u64));
> > > 
> > > The last time I asked Kent about this line, he didn’t want this.
> > 
> > 
> > Yes, the destination buffer isn't required to be nul terminated.
> > 
> > But it seems we should add a comment explaining that :)
> 
> I should have checked the mailing list before, but I will keep this in mind for my next contributions.
> I wonder if we should use memcpy in this case. This is also recommended by the security team here https://github.com/KSPP/linux/issues/90
> This will also prevent other people from trying to send a similar patch in the future.

Or better, a new helper: when we're copying to a fixed size buffer we
really want to zero out the rest of the buffer - we don't just want a
single terminating nul.

This has come up in other places in bcachefs, see __bch2_fs_log_msg() in
btree_update.c, and I would imagine the code for updating superblock
labels as well.