Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain; charset="UTF-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        syzbot+f7b556d1766502a69d85071d2ff08bd87be53d0f@syzkaller.appspotmail.com,
        "Eric Biggers" <ebiggers@google.com>, "Tejun Heo" <tj@kernel.org>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.992094030@decadent.org.uk>
Subject: [PATCH 3.16 229/410] libata: remove WARN() for DMA or PIO command
 without data
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 9173e5e80729c8434b8d27531527c5245f4a5594 upstream.

syzkaller hit a WARN() in ata_qc_issue() when writing to /dev/sg0.  This
happened because it issued a READ_6 command with no data buffer.

Just remove the WARN(), as it doesn't appear indicate a kernel bug.  The
expected behavior is to fail the command, which the code does.

Here's a reproducer that works in QEMU when /dev/sg0 refers to a disk of
the default type ("82371SB PIIX3 IDE"):

    #include <fcntl.h>
    #include <unistd.h>

    int main()
    {
            char buf[42] = { [36] = 0x8 /* READ_6 */ };

            write(open("/dev/sg0", O_RDWR), buf, sizeof(buf));
    }

Fixes: f92a26365a72 ("libata: change ATA_QCFLAG_DMAMAP semantics")
Reported-by: syzbot+f7b556d1766502a69d85071d2ff08bd87be53d0f@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/ata/libata-core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -5139,8 +5139,7 @@ void ata_qc_issue(struct ata_queued_cmd
 	 * We guarantee to LLDs that they will have at least one
 	 * non-zero sg if the command is a data command.
 	 */
-	if (WARN_ON_ONCE(ata_is_data(prot) &&
-			 (!qc->sg || !qc->n_elem || !qc->nbytes)))
+	if (ata_is_data(prot) && (!qc->sg || !qc->n_elem || !qc->nbytes))
 		goto sys_err;
 
 	if (ata_is_dma(prot) || (ata_is_pio(prot) &&