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Fri, 06 Feb 2026 13:26:50 -0800 (PST) MIME-Version: 1.0 References: <202601071226.8DF7C63@keescook> In-Reply-To: From: =?UTF-8?Q?Maciej_=C5=BBenczykowski?= Date: Fri, 6 Feb 2026 13:26:37 -0800 X-Gm-Features: AZwV_QguewADB-2xma46o3PunJjIPEerBNilNQhrGaSGk5f8ofWHwvj9j70yzs8 Message-ID: Subject: Re: KASAN vs realloc To: Maciej Wieczor-Retman Cc: Andrey Ryabinin , Kees Cook , joonki.min@samsung-slsi.corp-partner.google.com, Andrew Morton , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Marco Elver , Andrew Morton , Uladzislau Rezki , Danilo Krummrich , jiayuan.chen@linux.dev, syzbot+997752115a851cb0cf36@syzkaller.appspotmail.com, Maciej Wieczor-Retman , kasan-dev@googlegroups.com, Kernel hackers , linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 8423A140003 X-Stat-Signature: uhe3d9gf4oqgt9n5qb46axtc7c45ewgg X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770413211-915070 X-HE-Meta: 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 hkscvHli TbrA2QP8STe0U7s0ff51SvIwYkjjENkRZQMsiklRZdHAZAgm5X828+V5q40K5NOOIi9cHLd0z5p/5HN/Hp2AyR0b9/jrWAePTbTx1GMjdFs8LNBb4ewgL/wHbwW+TskXhXo3UzMPFnZXlJex4zMxFjknkAzf2zG2DIYmAEvO019aBpcCoF8UJZUYdjr0o36MDpLQm4Z+wyGsblMcAHGNwk2iQTrqFD1JqLnOTxyDtuy7cqkXo4YhCF5+bNMZIhgP15VTBfk3by35zrnHC8pOauYd4LctD3j1AV/cHDH76cbQPLIwUVGo1Gc+zMeTsCbMiyhm0MzsaUTRc7JPa10UuJzLDjGFf7FJiZNTEFzTOUIPqvipnPrcq/RkZfRGPeamXnhwD X-Bogosity: Ham, tests=bogofilter, spamicity=0.000019, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 6, 2026 at 12:14=E2=80=AFPM Maciej Wieczor-Retman wrote: > > From what I see kasan_poison_last_granule() is called through: > > __kasan_vrealloc() > --> __kasan_unpoison_vmalloc() > ----> kasan_unpoison() > ------> kasan_poison_last_granule() > > and the arguments are "addr + old_size" and "new_size - old_size" so it l= ooks > okay I think. Cool, thanks for checking. > On 2026-02-06 at 11:07:12 -0800, Maciej =C5=BBenczykowski wrote: > >While looking at: > > https://android-review.git.corp.google.com/c/kernel/common/+/3939998 > > UPSTREAM: mm/kasan: fix KASAN poisoning in vrealloc() > > > >I noticed a lack of symmetry - I'm not sure if it's a problem or not... > >but I'd have expected kasan_poison_last_granule() to be called > >regardless of whether the size shrunk or increased. > > > >It is of course possible this is handled automatically by > >__kasan_unpoison_vmalloc() - I haven't traced that deep, > >in general these functions seem to have a terrible api surface full of > >razors... with hidden assumptions about what is and is not granule > >aligned. > > -- > Kind regards > Maciej Wiecz=C3=B3r-Retman > -- Maciej =C5=BBenczykowski, Kernel Networking Developer @ Google