During fuzz testing, the following issue was discovered:
BUG: KMSAN: uninit-value in __dma_map_sg_attrs+0x217/0x310 __dma_map_sg_attrs+0x217/0x310 dma_map_sg_attrs+0x4a/0x70 ata_qc_issue+0x9f8/0x1420 __ata_scsi_queuecmd+0x1657/0x1740 ata_scsi_queuecmd+0x79a/0x920 scsi_queue_rq+0x4472/0x4f40 blk_mq_dispatch_rq_list+0x1cca/0x3ee0 __blk_mq_sched_dispatch_requests+0x458/0x630 blk_mq_sched_dispatch_requests+0x15b/0x340 __blk_mq_run_hw_queue+0xe5/0x250 __blk_mq_delay_run_hw_queue+0x138/0x780 blk_mq_run_hw_queue+0x4bb/0x7e0 blk_mq_sched_insert_request+0x2a7/0x4c0 blk_execute_rq+0x497/0x8a0 sg_io+0xbe0/0xe20 scsi_ioctl+0x2b36/0x3c60 sr_block_ioctl+0x319/0x440 blkdev_ioctl+0x80f/0xd70 __se_sys_ioctl+0x219/0x420 __x64_sys_ioctl+0x93/0xe0 x64_sys_call+0x1d6c/0x3ad0 do_syscall_64+0x4c/0xa0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8
Uninit was created at: __alloc_pages+0x5c0/0xc80 alloc_pages+0xe0e/0x1050 blk_rq_map_user_iov+0x2b77/0x6100 blk_rq_map_user_io+0x2fa/0x4d0 sg_io+0xad6/0xe20 scsi_ioctl+0x2b36/0x3c60 sr_block_ioctl+0x319/0x440 blkdev_ioctl+0x80f/0xd70 __se_sys_ioctl+0x219/0x420 __x64_sys_ioctl+0x93/0xe0 x64_sys_call+0x1d6c/0x3ad0 do_syscall_64+0x4c/0xa0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8
Bytes 14-15 of 16 are uninitialized Memory access of size 16 starts at ffff88800cbdb000
When processing the last unaligned element of the scatterlist, it is supplemented with missing bytes in the amount of pad_len. These bytes remain uninitialized, which leads to a problem.
Add zeroing pad_len bytes of padding by pad_offset offset before increasing its length. This ensures that the DMA does not receive uninitialized data and eliminates the KMSAN warning.
In this case, the pages are not located in highmem, but in the general case they might be, so kmap_local_page() is used for mapping.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Fixes: 40b01b9bbdf5 ("block: update bio according to DMA alignment padding") Co-developed-by: Boris Tonofa b.tonofa@ideco.ru Signed-off-by: Boris Tonofa b.tonofa@ideco.ru Signed-off-by: Petr Vaganov p.vaganov@ideco.ru --- drivers/scsi/scsi_lib.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 144c72f0737a..d287e24b6013 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1153,6 +1153,11 @@ blk_status_t scsi_alloc_sgtables(struct scsi_cmnd *cmd) if (blk_rq_bytes(rq) & rq->q->limits.dma_pad_mask) { unsigned int pad_len = (rq->q->limits.dma_pad_mask & ~blk_rq_bytes(rq)) + 1; + unsigned int pad_offset = last_sg->offset + last_sg->length; + void *vaddr = kmap_local_page(sg_page(last_sg)); + + memset(vaddr + pad_offset, 0, pad_len); + kunmap_local(vaddr);
last_sg->length += pad_len; cmd->extra_len += pad_len;