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Sun, 22 Mar 2026 06:55:08 -0700 (PDT) Received: from localhost.localdomain ([175.202.18.54]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35bd267fd96sm2553604a91.3.2026.03.22.06.55.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Mar 2026 06:55:08 -0700 (PDT) From: Jun Yeong Kim To: shaggy@kernel.org Cc: jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Jun Yeong Kim , syzbot+0be47376a6acbcba7f0d@syzkaller.appspotmail.com Subject: [PATCH v3] jfs: fix slab-out-of-bounds in dbAllocBits and dbFreeBits Date: Sun, 22 Mar 2026 22:54:23 +0900 Message-ID: <20260322135441.92788-1-junyeonggim5@gmail.com> X-Mailer: git-send-email 2.47.3 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" When the underlying loop device backend storage is dynamically changed (e.g., via LOOP_SET_FD), JFS fails to update its internal block allocation metadata. This causes dbAllocBits and dbFreeBits to use stale db_agl2size, producing an out-of-range agno value that leads to an out-of-bounds access on mp->db_agfree[agno]. Add bounds checks for agno in both dbAllocBits and dbFreeBits. If agno is negative or exceeds MAXAG, report the error via jfs_error() and return early to prevent the OOB access. Reported-by: syzbot+0be47376a6acbcba7f0d@syzkaller.appspotmail.com Tested-by: syzbot+0be47376a6acbcba7f0d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D0be47376a6acbcba7f0d Signed-off-by: Jun Yeong Kim --- fs/jfs/jfs_dmap.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c index cb3cda1390ad..c67ff5df0340 100644 --- a/fs/jfs/jfs_dmap.c +++ b/fs/jfs/jfs_dmap.c @@ -2142,6 +2142,12 @@ static void dbAllocBits(struct bmap * bmp, struct dm= ap * dp, s64 blkno, int size; s8 *leaf; =20 + agno =3D blkno >> bmp->db_agl2size; + if (agno < 0 || agno >=3D MAXAG) { + jfs_error(bmp->db_ipbmap->i_sb, "%s: agno %d out of range\n", __f= unc__, agno); + return; + } + /* pick up a pointer to the leaves of the dmap tree */ leaf =3D dp->tree.stree + LEAFIND; =20 @@ -2289,6 +2295,12 @@ static int dbFreeBits(struct bmap * bmp, struct dmap= * dp, s64 blkno, int rc =3D 0; int size; =20 + agno =3D blkno >> bmp->db_agl2size; + if (agno < 0 || agno >=3D MAXAG) { + jfs_error(bmp->db_ipbmap->i_sb, "%s: agno %d out of range\n", __f= unc__, agno); + return -EIO; + } + /* determine the bit number and word within the dmap of the * starting block. */ --=20 2.47.3 Changes in v3: - Add Tested-by tag from syzbot Changes in v2: - Fix correct function (dbAllocBits) instead of dbFreeBits - Add bounds check in dbFreeBits as well for consistency - Use jfs_error() instead of pr_err() - Use %s/__func__ instead of hardcoded function name - Fix indentation issues reported by checkpatch