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Message-ID: <51ee454cf93c24afbfc9f159a1b8428d9d6e3be7.camel@huaweicloud.com>
Subject: Re: [syzbot] [integrity?] [lsm?] KMSAN: uninit-value in
 ima_add_template_entry
From: Roberto Sassu <roberto.sassu@huaweicloud.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, syzbot
	 <syzbot+7bc44a489f0ef0670bd5@syzkaller.appspotmail.com>, 
	syzkaller-bugs@googlegroups.com, Gao Xiang <xiang@kernel.org>, Chao Yu
	 <chao@kernel.org>, Yue Hu <huyue2@coolpad.com>, Jeffle Xu
	 <jefflexu@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org, linux-erofs@lists.ozlabs.org, 
	linux-integrity@vger.kernel.org, zohar@linux.ibm.com
Date: Mon, 04 Mar 2024 09:15:21 +0100
In-Reply-To: <ab2a337d-c2dd-437d-9ab8-e3b837f1ff1a@I-love.SAKURA.ne.jp>
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	 <40746a9ae6d2e76d748ec0bf7710bba7e49a53ac.camel@huaweicloud.com>
	 <ab2a337d-c2dd-437d-9ab8-e3b837f1ff1a@I-love.SAKURA.ne.jp>
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On Sun, 2024-03-03 at 23:54 +0900, Tetsuo Handa wrote:
> On 2024/02/20 19:40, Roberto Sassu wrote:
> > On Mon, 2024-02-19 at 22:41 -0800, syzbot wrote:
> > > Hello,
> > >=20
> > > syzbot found the following issue on:
> > >=20
> > > HEAD commit:    4f5e5092fdbf Merge tag 'net-6.8-rc5' of git://git.ker=
nel.o..
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D135ba81c1=
80000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=3De3dd779fb=
a027968
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D7bc44a489f0=
ef0670bd5
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for=
 Debian) 2.40
>=20
> > I would add the VFS people in CC, in case they have some ideas.
>=20
> This is an erofs bug. Since the filesystem image in the reproducer
> is crafted, decompression generates bogus result and
> z_erofs_transform_plain() misbehaves.

Thank you Tetsuo, and Gao Xiang for fixing it!

Roberto

> You can obtain a single-threaded reproducer from
> https://syzkaller.appspot.com/x/repro.c?x=3D1256096a180000 with below dif=
f.
>=20
> ----------------------------------------
> --- old/1256096a180000.c
> +++ new/1256096a180000.c
> @@ -676,6 +676,6 @@
>    syscall(__NR_mmap, /*addr=3D*/0x21000000ul, /*len=3D*/0x1000ul, /*prot=
=3D*/0ul,
>            /*flags=3DMAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=
=3D*/-1,
>            /*offset=3D*/0ul);
> -  loop();
> +  execute_one();
>    return 0;
>  }
> ----------------------------------------
>=20
> With CONFIG_EROFS_FS_DEBUG=3Dy, the reproducer hits DBG_BUGON().
> With debug printk() shown below, you can get output shown below.
>=20
> ----------------------------------------
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index d4cee95af14c..f221133a0731 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -323,7 +323,11 @@ static int z_erofs_transform_plain(struct z_erofs_de=
compress_req *rq,
>  	unsigned int cur =3D 0, ni =3D 0, no, pi, po, insz, cnt;
>  	u8 *kin;
> =20
> -	DBG_BUGON(rq->outputsize > rq->inputsize);
> +	if (rq->outputsize > rq->inputsize) {
> +		pr_err("rq->inputsize=3D%u rq->outputsize=3D%u\n", rq->inputsize, rq->=
outputsize);
> +		pr_err("rq->pageofs_in=3D%u rq->pageofs_out=3D%u\n", rq->pageofs_in, r=
q->pageofs_out);
> +		pr_err("nrpages_in=3D%u nrpages_out=3D%u\n", nrpages_in, nrpages_out);
> +	}
>  	if (rq->alg =3D=3D Z_EROFS_COMPRESSION_INTERLACED) {
>  		cur =3D bs - (rq->pageofs_out & (bs - 1));
>  		pi =3D (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MASK;
> @@ -352,7 +356,8 @@ static int z_erofs_transform_plain(struct z_erofs_dec=
ompress_req *rq,
>  		do {
>  			no =3D (rq->pageofs_out + cur + pi) >> PAGE_SHIFT;
>  			po =3D (rq->pageofs_out + cur + pi) & ~PAGE_MASK;
> -			DBG_BUGON(no >=3D nrpages_out);
> +			if (no >=3D nrpages_out)
> +				pr_err("no=3D%u nrpages_out=3D%u\n", no, nrpages_out);
>  			cnt =3D min(insz - pi, PAGE_SIZE - po);
>  			if (rq->out[no] =3D=3D rq->in[ni]) {
>  				memmove(kin + po,
> @@ -366,7 +371,8 @@ static int z_erofs_transform_plain(struct z_erofs_dec=
ompress_req *rq,
>  		} while (pi < insz);
>  		kunmap_local(kin);
>  	}
> -	DBG_BUGON(ni > nrpages_in);
> +	if (ni > nrpages_in)
> +		pr_err("ni=3D%u nrpages_in=3D%u\n", ni, nrpages_in);
>  	return 0;
>  }
> =20
> ----------------------------------------
>=20
> ----------------------------------------
> [  138.991810][ T2983] loop0: detected capacity change from 0 to 16
> [  139.804002][ T2983] erofs: (device loop0): mounted with root inode @ n=
id 36.
> [  139.810464][   T87] erofs: rq->inputsize=3D4096 rq->outputsize=3D8194
> [  139.821540][   T87] erofs: rq->pageofs_in=3D0 rq->pageofs_out=3D0
> [  139.824347][   T87] erofs: nrpages_in=3D1 nrpages_out=3D3
> [  139.827008][   T87] erofs: ni=3D3 nrpages_in=3D1
> [  139.873777][ T2983] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> [  139.881268][ T2983] BUG: KMSAN: uninit-value in ima_add_template_entry=
+0x626/0xa80
> ----------------------------------------
>=20
> #syz set subsystems: erofs