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Wed, 06 May 2026 12:23:25 -0700 (PDT) Received: from li-4c4c4544-0032-4210-804c-c3c04f423534.ibm.com ([2600:1700:6476:1430::29]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7bd665464ccsm83249867b3.11.2026.05.06.12.23.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2026 12:23:24 -0700 (PDT) Message-ID: <00306449e9bb0703aedc71b01fea2b04e33b2725.camel@redhat.com> Subject: Re: [PATCH v2 2/2] hfs/hfsplus: zero-initialize buffer in hfs_bnode_read From: Viacheslav Dubeyko To: Tristan Madani , Viacheslav Dubeyko Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 06 May 2026 12:23:23 -0700 In-Reply-To: <20260505111300.3592757-3-tristmd@gmail.com> References: <20260501110218.29906-1-tristmd@gmail.com> <20260505111300.3592757-1-tristmd@gmail.com> <20260505111300.3592757-3-tristmd@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.0 (3.60.0-1.fc44app2) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-05-05 at 11:12 +0000, Tristan Madani wrote: > From: Tristan Madani >=20 > hfs_bnode_read() can return early without writing to the output buffer > when is_bnode_offset_valid() fails or when check_and_correct_requested_ > length() corrects the length to zero. Callers such as hfs_bnode_read_ > u16() and hfs_bnode_read_u8() pass stack-allocated buffers and use the > result unconditionally, leading to KMSAN uninit-value reports. >=20 > Rather than initializing at each individual call site, zero the buffer > at the start of hfs_bnode_read() before any validation checks. This > ensures all callers in both hfs and hfsplus get a deterministic zero > value regardless of which early-return path is taken. >=20 > Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3D217eb327242d08197efb > Tested-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com > Fixes: a431930c9bac ("hfs: fix slab-out-of-bounds in hfs_bnode_read()") > Cc: stable@vger.kernel.org > Signed-off-by: Tristan Madani > --- > fs/hfs/bnode.c | 2 ++ > fs/hfsplus/bnode.c | 2 ++ > 2 files changed, 4 insertions(+) >=20 > diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c > index 9571f33b91085..25cef62fbba6d 100644 > --- a/fs/hfs/bnode.c > +++ b/fs/hfs/bnode.c > @@ -64,6 +64,8 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, = u32 off, u32 len) > u32 bytes_read; > u32 bytes_to_read; > =20 > + memset(buf, 0, len); > + > if (!is_bnode_offset_valid(node, off)) > return; > =20 > diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c > index f8b5a8ae58ff5..14d1af2c7ba93 100644 > --- a/fs/hfsplus/bnode.c > +++ b/fs/hfsplus/bnode.c > @@ -25,6 +25,8 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, = u32 off, u32 len) > struct page **pagep; > u32 l; > =20 > + memset(buf, 0, len); > + > if (!is_bnode_offset_valid(node, off)) > return; > =20 We are returning back to the same my question. What if the caller of hfs_bnode_read() provides the len =3D=3D 0 somehow but the buffer has not z= ero size on the caller side? I assume that memset() will do nothing and the buffer s= till be not initialized. Am I correct here? Thanks, Slava.