Patch "libata: remove WARN() for DMA or PIO command without data" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

libata: remove WARN() for DMA or PIO command without data

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
libata-remove-warn-for-dma-or-pio-command-without-data.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Biggers <[email protected]>
Date: Sat, 3 Feb 2018 20:33:27 -0800
Subject: libata: remove WARN() for DMA or PIO command without data

From: Eric Biggers <[email protected]>

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));
    }

---
 drivers/ata/libata-core.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

@@ -5401,8 +5401,7 @@ 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) &&

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/libata-fix-length-validation-of-atapi-relayed-scsi-commands.patch queue-4.15/libata-remove-warn-for-dma-or-pio-command-without-data.patch queue-4.15/libata-don-t-try-to-pass-through-ncq-commands-to-non-ncq-devices.patch