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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48724460767sm6267511f8f.13.2026.09.19.04.04.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 04:04:58 -0700 (PDT) Date: Sat, 19 Sep 2026 12:04:56 +0100 From: David Laight To: Karl Mehltretter Cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Rasmus Villemoes , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Catalin Marinas , Kees Cook , "Gustavo A . R . Silva" , Arnd Bergmann , Greg Kroah-Hartman , Shuah Khan , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v3 3/5] slab: handle ERR_PTR values in kfree and hardened usercopy Message-ID: <20260919120456.5575e0a4@pumpkin> In-Reply-To: <20260903203720.63689-4-kmehltretter@gmail.com> References: <20260903203720.63689-1-kmehltretter@gmail.com> <20260903203720.63689-4-kmehltretter@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 3 Sep 2026 22:37:18 +0200 Karl Mehltretter wrote: > Passing an ERR_PTR to kfree() currently reaches virt_to_page() and may > fault. Warn and return instead, leaving the bad caller visible without > using the pointer as allocator metadata. > > Also reject ERR_PTR values in hardened usercopy. Keep both checks > separate from ZERO_OR_NULL_PTR(), whose exact matching is required by > krealloc(). > > Link: https://lore.kernel.org/r/CAG48ez05QVn6_gQ2TBrRa1a_DWQoaSSYubUsu5YMWxx-gqMijQ@mail.gmail.com > Link: https://lore.kernel.org/r/202608111716.0FA9DB17@keescook > Link: https://github.com/KSPP/linux/issues/93 > Assisted-by: LLM > Signed-off-by: Karl Mehltretter > --- > mm/slub.c | 3 +++ > mm/usercopy.c | 3 +++ > 2 files changed, 6 insertions(+) > > diff --git a/mm/slub.c b/mm/slub.c > index f9b56cb439e7..027b44dd7f07 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6780,6 +6780,9 @@ void kfree(const void *object) > if (unlikely(ZERO_OR_NULL_PTR(object))) > return; > > + if (WARN_ON(IS_ERR(object))) > + return; > + Since kfree isn't usually called with NULL it is likely to be better to have a initial single check for all the error cases. Something like: if (unlikely((unsigned long)object + MAX_ERRNO <= MAX_ERRNO + ZERO_SIZE_PTR) { WARN_ON(!ZERO_OR_NULL_PTR(object)) return; } Although is would save a lot of code elsewhere if kfree(-errno) were valid. David > page = virt_to_page(object); > slab = page_slab(page); > if (!slab) { > diff --git a/mm/usercopy.c b/mm/usercopy.c > index 5de7a518b1b1..c8d8703544c6 100644 > --- a/mm/usercopy.c > +++ b/mm/usercopy.c > @@ -157,6 +157,9 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n, > /* Reject if NULL or ZERO-allocation. */ > if (ZERO_OR_NULL_PTR(ptr)) > usercopy_abort("null address", NULL, to_user, ptr, n); > + > + if (IS_ERR_VALUE(ptr)) > + usercopy_abort("ERR_PTR", NULL, to_user, ptr, n); > } > > static inline void check_heap_object(const void *ptr, unsigned long n,