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Subject[PATCH 3.18 05/93] libata: remove WARN() for DMA or PIO command without data
Date
3.18-stable 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
Cc: <stable@vger.kernel.org> # v2.6.25+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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
@@ -5109,8 +5109,7 @@ 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) &&

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