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([2405:201:d019:4872:bd32:daa5:57cd:7884]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7a2300f25cdsm1520149b3a.35.2025.10.17.22.32.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Oct 2025 22:32:16 -0700 (PDT) From: Sukrut Heroorkar To: Dave Kleikamp , Rand Deeb , Edward Adam Davis , Ghanshyam Agrawal , Nihar Chaithanya , Vasiliy Kovalev , Sukrut Heroorkar , Arnaud Lecomte , jfs-discussion@lists.sourceforge.net (open list:JFS FILESYSTEM), linux-kernel@vger.kernel.org (open list) Cc: skhan@linux.foundation.org, david.hunter.linux@gmail.com, syzbot+4b717071f1eecb2972df@syzkaller.appspotmail.com Subject: [PATCH] jfs: validate budmin to prevent shift-out-of-bounds in dbAllocAG() Date: Sat, 18 Oct 2025 11:00:25 +0530 Message-ID: <20251018053029.226506-1-hsukrut3@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" syzbot reported "UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:1440:48 shift exponent -1 is negative". The budmin value can have a negative value and cause shift-out-of- -bounds from UBSAN. Add a check on budmin immediately after reading it from the metapage, and return an error if it's negative. This prevents UBSAN reports and correctly treats corrupted metadata as an I/O error. Reported-by: syzbot+4b717071f1eecb2972df@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D4b717071f1eecb2972df Tested-by: syzbot+4b717071f1eecb2972df@syzkaller.appspotmail.com Signed-off-by: Sukrut Heroorkar --- fs/jfs/jfs_dmap.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c index cdfa699cd7c8..76f4b9322034 100644 --- a/fs/jfs/jfs_dmap.c +++ b/fs/jfs/jfs_dmap.c @@ -1372,6 +1372,12 @@ dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, = int l2nb, s64 * results) dcp =3D (struct dmapctl *) mp->data; budmin =3D dcp->budmin; =20 + if (unlikely(budmin < 0)) { + jfs_err("JFS: dmapctl corruption: budmin=3D%d", budmin); + release_metapage(mp); + return -EIO; + } + if (dcp->leafidx !=3D cpu_to_le32(CTLLEAFIND)) { jfs_error(bmp->db_ipbmap->i_sb, "Corrupt dmapctl page\n"); release_metapage(mp); --=20 2.43.0