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([2405:201:682f:389d:2365:8a49:f4ff:aeb]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a3e3c48dc1sm191795945ad.40.2026.01.13.00.40.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Jan 2026 00:40:44 -0800 (PST) From: Deepanshu Kartikey To: brauner@kernel.org, viro@zeniv.linux.org.uk Cc: mjguzik@gmail.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Deepanshu Kartikey , syzbot+9c4e33e12283d9437c25@syzkaller.appspotmail.com Subject: [PATCH] romfs: check sb_set_blocksize() return value Date: Tue, 13 Jan 2026 14:10:37 +0530 Message-ID: <20260113084037.1167887-1-kartikey406@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" romfs_fill_super() ignores the return value of sb_set_blocksize(), which can fail if the requested block size is incompatible with the block device's configuration. This can be triggered by setting a loop device's block size larger than PAGE_SIZE using ioctl(LOOP_SET_BLOCK_SIZE, 32768), then mounting a romfs filesystem on that device. When sb_set_blocksize(sb, ROMBSIZE) is called with ROMBSIZE=3D4096 but the device has logical_block_size=3D32768, bdev_validate_blocksize() fails because the requested size is smaller than the device's logical block size. sb_set_blocksize() returns 0 (failure), but romfs ignores this and continues mounting. The superblock's block size remains at the device's logical block size (32768). Later, when sb_bread() attempts I/O with this oversized block size, it triggers a kernel BUG in folio_set_bh(): kernel BUG at fs/buffer.c:1582! BUG_ON(size > PAGE_SIZE); Fix by checking the return value of sb_set_blocksize() and failing the mount with -EINVAL if it returns 0. Reported-by: syzbot+9c4e33e12283d9437c25@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D9c4e33e12283d9437c25 Signed-off-by: Deepanshu Kartikey --- fs/romfs/super.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/romfs/super.c b/fs/romfs/super.c index 360b00854115..ac55193bf398 100644 --- a/fs/romfs/super.c +++ b/fs/romfs/super.c @@ -458,7 +458,10 @@ static int romfs_fill_super(struct super_block *sb, st= ruct fs_context *fc) =20 #ifdef CONFIG_BLOCK if (!sb->s_mtd) { - sb_set_blocksize(sb, ROMBSIZE); + if (!sb_set_blocksize(sb, ROMBSIZE)) { + errorf(fc, "romfs: unable to set blocksize\n"); + return -EINVAL; + } } else { sb->s_blocksize =3D ROMBSIZE; sb->s_blocksize_bits =3D blksize_bits(ROMBSIZE); --=20 2.43.0