| Message ID | 20190810211903.6572-1-dmitry.fomichev@wdc.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tcmu: avoid use-after-free after command timeout | expand |
On 08/10/2019 04:19 PM, Dmitry Fomichev wrote: > In tcmu_handle_completion() function, the variable called read_len is > always initialized with a value taken from se_cmd structure. If this > function is called to complete an expired (timed out) out command, the > session command pointed by se_cmd is likely to be already deallocated by > the target core at that moment. As the result, this access triggers a > use-after-free warning from KASAN. > > This patch fixes the code not to touch se_cmd when completing timed out > TCMU commands. It also resets the pointer to se_cmd at the time when the > TCMU_CMD_BIT_EXPIRED flag is set because it is going to become invalid > after calling target_complete_cmd() later in the same function, > tcmu_check_expired_cmd(). > > Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com> > --- > drivers/target/target_core_user.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c > index 04eda111920e..a0231491fa36 100644 > --- a/drivers/target/target_core_user.c > +++ b/drivers/target/target_core_user.c > @@ -1132,14 +1132,16 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry * > struct se_cmd *se_cmd = cmd->se_cmd; > struct tcmu_dev *udev = cmd->tcmu_dev; > bool read_len_valid = false; > - uint32_t read_len = se_cmd->data_length; > + uint32_t read_len; > > /* > * cmd has been completed already from timeout, just reclaim > * data area space and free cmd > */ > - if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) > + if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) { > + WARN_ON_ONCE(se_cmd); If you are adding a warn here, I think you want to also add a warn in tcmu_reset_ring where there is another code path we do the same sequence of operations where we check the bit then access the se_cmd after if not set.
On Sat, 2019-08-10 at 18:55 -0500, Mike Christie wrote: > On 08/10/2019 04:19 PM, Dmitry Fomichev wrote: > > In tcmu_handle_completion() function, the variable called read_len is > > always initialized with a value taken from se_cmd structure. If this > > function is called to complete an expired (timed out) out command, the > > session command pointed by se_cmd is likely to be already deallocated by > > the target core at that moment. As the result, this access triggers a > > use-after-free warning from KASAN. > > > > This patch fixes the code not to touch se_cmd when completing timed out > > TCMU commands. It also resets the pointer to se_cmd at the time when the > > TCMU_CMD_BIT_EXPIRED flag is set because it is going to become invalid > > after calling target_complete_cmd() later in the same function, > > tcmu_check_expired_cmd(). > > > > Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com> > > --- > > drivers/target/target_core_user.c | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c > > index 04eda111920e..a0231491fa36 100644 > > --- a/drivers/target/target_core_user.c > > +++ b/drivers/target/target_core_user.c > > @@ -1132,14 +1132,16 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry * > > struct se_cmd *se_cmd = cmd->se_cmd; > > struct tcmu_dev *udev = cmd->tcmu_dev; > > bool read_len_valid = false; > > - uint32_t read_len = se_cmd->data_length; > > + uint32_t read_len; > > > > /* > > * cmd has been completed already from timeout, just reclaim > > * data area space and free cmd > > */ > > - if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) > > + if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) { > > + WARN_ON_ONCE(se_cmd); > > If you are adding a warn here, I think you want to also add a warn in > tcmu_reset_ring where there is another code path we do the same sequence > of operations where we check the bit then access the se_cmd after if not > set. > Mike, Good point, thanks. I am going to send out the updated version of the patch. Dmitry
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c index 04eda111920e..a0231491fa36 100644 --- a/drivers/target/target_core_user.c +++ b/drivers/target/target_core_user.c @@ -1132,14 +1132,16 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry * struct se_cmd *se_cmd = cmd->se_cmd; struct tcmu_dev *udev = cmd->tcmu_dev; bool read_len_valid = false; - uint32_t read_len = se_cmd->data_length; + uint32_t read_len; /* * cmd has been completed already from timeout, just reclaim * data area space and free cmd */ - if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) + if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) { + WARN_ON_ONCE(se_cmd); goto out; + } list_del_init(&cmd->queue_entry); @@ -1152,6 +1154,7 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry * goto done; } + read_len = se_cmd->data_length; if (se_cmd->data_direction == DMA_FROM_DEVICE && (entry->hdr.uflags & TCMU_UFLAG_READ_LEN) && entry->rsp.read_len) { read_len_valid = true; @@ -1307,6 +1310,7 @@ static int tcmu_check_expired_cmd(int id, void *p, void *data) */ scsi_status = SAM_STAT_CHECK_CONDITION; list_del_init(&cmd->queue_entry); + cmd->se_cmd = NULL; } else { list_del_init(&cmd->queue_entry); idr_remove(&udev->commands, id);
In tcmu_handle_completion() function, the variable called read_len is always initialized with a value taken from se_cmd structure. If this function is called to complete an expired (timed out) out command, the session command pointed by se_cmd is likely to be already deallocated by the target core at that moment. As the result, this access triggers a use-after-free warning from KASAN. This patch fixes the code not to touch se_cmd when completing timed out TCMU commands. It also resets the pointer to se_cmd at the time when the TCMU_CMD_BIT_EXPIRED flag is set because it is going to become invalid after calling target_complete_cmd() later in the same function, tcmu_check_expired_cmd(). Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com> --- drivers/target/target_core_user.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)