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authorMauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>2016-12-15 11:48:18 -0600
committerJens Axboe <axboe@fb.com>2016-12-19 08:34:17 -0700
commit25cdb64510644f3e854d502d69c73f21c6df88a9 (patch)
tree45b216fe60f9508eb425ab87edf584ec16c64c1d /block
parente8465447d2f3366069115f7453153561ac9a1220 (diff)
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block: allow WRITE_SAME commands with the SG_IO ioctl
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>
Diffstat (limited to 'block')
-rw-r--r--block/scsi_ioctl.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 0774799942e0..c6fee7437be4 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -182,6 +182,9 @@ static void blk_set_cmd_filter_defaults(struct blk_cmd_filter *filter)
__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);