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

[Kent Overstreet]

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@xxxxxxxxx> 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@xxxxxxxxxxxxxx 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@xxxxxxxxxxxxxx
> > > > ---
> > > > 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.