| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.18 109/124] block: allow WRITE_SAME commands with the SG_IO ioctl | Date | Thu, 20 Apr 2017 08:36:24 +0200 |
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3.18-stable review patch. If anyone has any objections, please let me know.
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From: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
commit 25cdb64510644f3e854d502d69c73f21c6df88a9 upstream.
The WRITE_SAME commands are not present in the blk_default_cmd_filter write_ok list, and thus are failed with -EPERM when the SG_IO ioctl() is executed without CAP_SYS_RAWIO capability (e.g., unprivileged users). [ sg_io() -> blk_fill_sghdr_rq() > blk_verify_command() -> -EPERM ]
The problem can be reproduced with the sg_write_same command
# sg_write_same --num 1 --xferlen 512 /dev/sda #
# capsh --drop=cap_sys_rawio -- -c \ 'sg_write_same --num 1 --xferlen 512 /dev/sda' Write same: pass through os error: Operation not permitted #
For comparison, the WRITE_VERIFY command does not observe this problem, since it is in that list:
# capsh --drop=cap_sys_rawio -- -c \ 'sg_write_verify --num 1 --ilen 512 --lba 0 /dev/sda' #
So, this patch adds the WRITE_SAME commands to the list, in order for the SG_IO ioctl to finish successfully:
# capsh --drop=cap_sys_rawio -- -c \ 'sg_write_same --num 1 --xferlen 512 /dev/sda' #
That case happens to be exercised by QEMU KVM guests with 'scsi-block' devices (qemu "-device scsi-block" [1], libvirt "<disk type='block' device='lun'>" [2]), which employs the SG_IO ioctl() and runs as an unprivileged user (libvirt-qemu).
In that scenario, when a filesystem (e.g., ext4) performs its zero-out calls, which are translated to write-same calls in the guest kernel, and then into SG_IO ioctls to the host kernel, SCSI I/O errors may be observed in the guest:
[...] sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [...] sd 0:0:0:0: [sda] tag#0 Sense Key : Aborted Command [current] [...] sd 0:0:0:0: [sda] tag#0 Add. Sense: I/O process terminated [...] sd 0:0:0:0: [sda] tag#0 CDB: Write Same(10) 41 00 01 04 e0 78 00 00 08 00 [...] blk_update_request: I/O error, dev sda, sector 17096824
Links: [1] http://git.qemu.org/?p=qemu.git;a=commit;h=336a6915bc7089fb20fea4ba99972ad9a97c5f52 [2] https://libvirt.org/formatdomain.html#elementsDisks (see 'disk' -> 'device')
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com> Signed-off-by: Brahadambal Srinivasan <latha@linux.vnet.ibm.com> Reported-by: Manjunatha H R <manjuhr1@in.ibm.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- block/scsi_ioctl.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/block/scsi_ioctl.c +++ b/block/scsi_ioctl.c @@ -182,6 +182,9 @@ static void blk_set_cmd_filter_defaults( __set_bit(WRITE_16, filter->write_ok); __set_bit(WRITE_LONG, filter->write_ok); __set_bit(WRITE_LONG_2, filter->write_ok); + __set_bit(WRITE_SAME, filter->write_ok); + __set_bit(WRITE_SAME_16, filter->write_ok); + __set_bit(WRITE_SAME_32, filter->write_ok); __set_bit(ERASE, filter->write_ok); __set_bit(GPCMD_MODE_SELECT_10, filter->write_ok); __set_bit(MODE_SELECT, filter->write_ok);
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