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Tue, 31 Mar 2026 07:33:55 -0700 (PDT) Date: Tue, 31 Mar 2026 16:33:53 +0200 From: Petr Mladek To: Josh Law Cc: Steven Rostedt , Andy Shevchenko , Rasmus Villemoes , Sergey Senozhatsky , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] lib/vsprintf: add missing (u8) cast in format_decode() lookup Message-ID: References: <20260324224940.50508-1-objecting@objecting.org> <20260324224940.50508-5-objecting@objecting.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260324224940.50508-5-objecting@objecting.org> On Tue 2026-03-24 22:49:40, Josh Law wrote: > The first lookup into the format_state table correctly casts to (u8) > at line 2778, but the second lookup after consuming a length qualifier > does not. On signed-char platforms, a byte >= 0x80 sign-extends to a > negative index, reading before the array. > > Add the same (u8) cast for consistency. > > Signed-off-by: Josh Law > --- > lib/vsprintf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index 2758096b6f53..3108823e8c22 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -2783,7 +2783,7 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec) > fmt.str++; > } > fmt.str++; > - p = lookup_state + *fmt.str; > + p = lookup_state + (u8)*fmt.str; > } > if (p->state) { > if (p->base) This makes sense. Even though the current code is safe as pointed out by Andy. Reviewed-by: Petr Mladek Best Regards, Petr