Messages in this thread | | | Date | Mon, 6 Feb 2023 19:50:42 +0000 | From | "Dr. David Alan Gilbert" <> | Subject | Re: [PATCH] jfs: Use unsigned variable for length calculations |
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* Kees Cook (keescook@chromium.org) wrote: > On Sat, Feb 04, 2023 at 08:25:45PM +0000, Dr. David Alan Gilbert wrote: > > * Kees Cook (keescook@chromium.org) wrote: > > > To avoid confusing the compiler about possible negative sizes, switch > > > "ssize" which can never be negative from int to u32. Seen with GCC 13: > > > > > > ../fs/jfs/namei.c: In function 'jfs_symlink': ../include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' pointer overflow between offset 0 and size [-2147483648, -1] > > > [-Warray-bounds=] > > > 57 | #define __underlying_memcpy __builtin_memcpy > > > | ^ > > > ... > > > ../fs/jfs/namei.c:950:17: note: in expansion of macro 'memcpy' > > > 950 | memcpy(ip->i_link, name, ssize); > > > | ^~~~~~ > > > > > > Cc: Dave Kleikamp <shaggy@kernel.org> > > > Cc: Christian Brauner <brauner@kernel.org> > > > Cc: Dave Chinner <dchinner@redhat.com> > > > Cc: jfs-discussion@lists.sourceforge.net > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > --- > > > fs/jfs/namei.c | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c > > > index b29d68b5eec5..494b9f4043cf 100644 > > > --- a/fs/jfs/namei.c > > > +++ b/fs/jfs/namei.c > > > @@ -876,7 +876,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip, > > > tid_t tid; > > > ino_t ino = 0; > > > struct component_name dname; > > > - int ssize; /* source pathname size */ > > > + u32 ssize; /* source pathname size */ > > > > Had you considered using size_t - this is set from a strlen and used by a memcpy > > that both talk size_t. > > I considered that, but I've had other maintainers upset about doubling > the variable size.
I bet at least on some platforms it's cheaper as the 64 bit.
> I opted to keep the variable 32-bit here, so the > machine code would only change to lose signed-ness.
Fair enough.
Dave
> -Kees > > -- > Kees Cook -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/
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