3.16.57-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit 058f58e235cbe03e923b30ea7c49995a46a8725f upstream.
syzkaller reported a crash in ata_bmdma_fill_sg() when writing to /dev/sg1. The immediate cause was that the ATA command's scatterlist was not DMA-mapped, which causes 'pi - 1' to underflow, resulting in a write to 'qc->ap->bmdma_prd[0xffffffff]'.
Strangely though, the flag ATA_QCFLAG_DMAMAP was set in qc->flags. The root cause is that when __ata_scsi_queuecmd() is preparing to relay a SCSI command to an ATAPI device, it doesn't correctly validate the CDB length before copying it into the 16-byte buffer 'cdb' in 'struct ata_queued_cmd'. Namely, it validates the fixed CDB length expected based on the SCSI opcode but not the actual CDB length, which can be larger due to the use of the SG_NEXT_CMD_LEN ioctl. Since 'flags' is the next member in ata_queued_cmd, a buffer overflow corrupts it.
Fix it by requiring that the actual CDB length be <= 16 (ATAPI_CDB_LEN).
[Really it seems the length should be required to be <= dev->cdb_len, but the current behavior seems to have been intentionally introduced by commit 607126c2a21c ("libata-scsi: be tolerant of 12-byte ATAPI commands in 16-byte CDBs") to work around a userspace bug in mplayer. Probably the workaround is no longer needed (mplayer was fixed in 2007), but continuing to allow lengths to up 16 appears harmless for now.]
Here's a reproducer that works in QEMU when /dev/sg1 refers to the CD-ROM drive that qemu-system-x86_64 creates by default:
#include <fcntl.h> #include <sys/ioctl.h> #include <unistd.h>
#define SG_NEXT_CMD_LEN 0x2283
int main() { char buf[53] = { [36] = 0x7e, [52] = 0x02 }; int fd = open("/dev/sg1", O_RDWR); ioctl(fd, SG_NEXT_CMD_LEN, &(int){ 17 }); write(fd, buf, sizeof(buf)); }
The crash was:
BUG: unable to handle kernel paging request at ffff8cb97db37ffc IP: ata_bmdma_fill_sg drivers/ata/libata-sff.c:2623 [inline] IP: ata_bmdma_qc_prep+0xa4/0xc0 drivers/ata/libata-sff.c:2727 PGD fb6c067 P4D fb6c067 PUD 0 Oops: 0002 [#1] SMP CPU: 1 PID: 150 Comm: syz_ata_bmdma_q Not tainted 4.15.0-next-20180202 #99 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014 [...] Call Trace: ata_qc_issue+0x100/0x1d0 drivers/ata/libata-core.c:5421 ata_scsi_translate+0xc9/0x1a0 drivers/ata/libata-scsi.c:2024 __ata_scsi_queuecmd drivers/ata/libata-scsi.c:4326 [inline] ata_scsi_queuecmd+0x8c/0x210 drivers/ata/libata-scsi.c:4375 scsi_dispatch_cmd+0xa2/0xe0 drivers/scsi/scsi_lib.c:1727 scsi_request_fn+0x24c/0x530 drivers/scsi/scsi_lib.c:1865 __blk_run_queue_uncond block/blk-core.c:412 [inline] __blk_run_queue+0x3a/0x60 block/blk-core.c:432 blk_execute_rq_nowait+0x93/0xc0 block/blk-exec.c:78 sg_common_write.isra.7+0x272/0x5a0 drivers/scsi/sg.c:806 sg_write+0x1ef/0x340 drivers/scsi/sg.c:677 __vfs_write+0x31/0x160 fs/read_write.c:480 vfs_write+0xa7/0x160 fs/read_write.c:544 SYSC_write fs/read_write.c:589 [inline] SyS_write+0x4d/0xc0 fs/read_write.c:581 do_syscall_64+0x5e/0x110 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x21/0x86
Fixes: 607126c2a21c ("libata-scsi: be tolerant of 12-byte ATAPI commands in 16-byte CDBs") Reported-by: syzbot+1ff6f9fcc3c35f1c72a95e26528c8e7e3276e4da@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-scsi.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/drivers/ata/libata-scsi.c +++ b/drivers/ata/libata-scsi.c @@ -3435,7 +3435,9 @@ static inline int __ata_scsi_queuecmd(st if (likely((scsi_op != ATA_16) || !atapi_passthru16)) { /* relay SCSI command to ATAPI device */ int len = COMMAND_SIZE(scsi_op); - if (unlikely(len > scmd->cmd_len || len > dev->cdb_len)) + if (unlikely(len > scmd->cmd_len || + len > dev->cdb_len || + scmd->cmd_len > ATAPI_CDB_LEN)) goto bad_cdb_len;
xlat_func = atapi_xlat;