2020-11-12 19:14:59

by Lukas Bulwahn

Subject: [PATCH] USB: storage: avoid use of uninitialized values in error path

When usb_stor_bulk_transfer_sglist() returns with USB_STOR_XFER_ERROR, it
returns without writing to its parameter *act_len.

Further, the two callers of usb_stor_bulk_transfer_sglist():

usb_stor_bulk_srb() and
usb_stor_bulk_transfer_sg(),

use the passed variable partial without checking the return value. Hence,
the uninitialized value of partial is then used in the further execution
of those two functions.

Clang-analyzer detects this potential control and data flow and warns:

drivers/usb/storage/transport.c:469:40:
warning: The right operand of '-' is a garbage value
[clang-analyzer-core.UndefinedBinaryOperatorResult]
scsi_set_resid(srb, scsi_bufflen(srb) - partial);
^

drivers/usb/storage/transport.c:495:15:
warning: Assigned value is garbage or undefined
[clang-analyzer-core.uninitialized.Assign]
length_left -= partial;
^

When a transfer error occurs, the *act_len value is probably ignored by the
higher layers. But it won't hurt to set it to a valid number, just in case.

For the two early-return paths in usb_stor_bulk_transfer_sglist(), the
amount of data transferred is 0. So if act_len is not NULL, set *act_len
to 0 in those paths. That makes clang-analyzer happy.

Proposal was discussed in this mail thread:

Link: https://lore.kernel.org/linux-usb/alpine.DEB.2.21.2011112146110.13119@felia/

Signed-off-by: Lukas Bulwahn <[email protected]>
---
applies cleanly on current master and next-20201112

I did some basic compile testing...

Alan, Greg, please pick this minor non-urgent clean-up patch.

drivers/usb/storage/transport.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index 238a8088e17f..5eb895b19c55 100644
--- a/drivers/usb/storage/transport.c
+++ b/drivers/usb/storage/transport.c
@@ -416,7 +416,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,

/* don't submit s-g requests during abort processing */
if (test_bit(US_FLIDX_ABORTING, &us->dflags))
- return USB_STOR_XFER_ERROR;
+ goto usb_stor_xfer_error;

/* initialize the scatter-gather request block */
usb_stor_dbg(us, "xfer %u bytes, %d entries\n", length, num_sg);
@@ -424,7 +424,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
sg, num_sg, length, GFP_NOIO);
if (result) {
usb_stor_dbg(us, "usb_sg_init returned %d\n", result);
- return USB_STOR_XFER_ERROR;
+ goto usb_stor_xfer_error;
}

/*
@@ -452,6 +452,11 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
*act_len = us->current_sg.bytes;
return interpret_urb_result(us, pipe, length, result,
us->current_sg.bytes);
+
+usb_stor_xfer_error:
+ if (act_len)
+ *act_len = 0;
+ return USB_STOR_XFER_ERROR;
}

/*
--
2.17.1

2020-11-12 19:30:40

by Alan Stern

Subject: Re: [PATCH] USB: storage: avoid use of uninitialized values in error path

On Thu, Nov 12, 2020 at 08:12:55PM +0100, Lukas Bulwahn wrote:
> When usb_stor_bulk_transfer_sglist() returns with USB_STOR_XFER_ERROR, it
> returns without writing to its parameter *act_len.
>
> Further, the two callers of usb_stor_bulk_transfer_sglist():
>
> usb_stor_bulk_srb() and
> usb_stor_bulk_transfer_sg(),
>
> use the passed variable partial without checking the return value. Hence,
> the uninitialized value of partial is then used in the further execution
> of those two functions.
>
> Clang-analyzer detects this potential control and data flow and warns:
>
> drivers/usb/storage/transport.c:469:40:
> warning: The right operand of '-' is a garbage value
> [clang-analyzer-core.UndefinedBinaryOperatorResult]
> scsi_set_resid(srb, scsi_bufflen(srb) - partial);
> ^
>
> drivers/usb/storage/transport.c:495:15:
> warning: Assigned value is garbage or undefined
> [clang-analyzer-core.uninitialized.Assign]
> length_left -= partial;
> ^
>
> When a transfer error occurs, the *act_len value is probably ignored by the
> higher layers. But it won't hurt to set it to a valid number, just in case.
>
> For the two early-return paths in usb_stor_bulk_transfer_sglist(), the
> amount of data transferred is 0. So if act_len is not NULL, set *act_len
> to 0 in those paths. That makes clang-analyzer happy.
>
> Proposal was discussed in this mail thread:
>
> Link: https://lore.kernel.org/linux-usb/alpine.DEB.2.21.2011112146110.13119@felia/
>
> Signed-off-by: Lukas Bulwahn <[email protected]>
> ---
> applies cleanly on current master and next-20201112
>
> I did some basic compile testing...
>
> Alan, Greg, please pick this minor non-urgent clean-up patch.
>
> drivers/usb/storage/transport.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
> index 238a8088e17f..5eb895b19c55 100644
> --- a/drivers/usb/storage/transport.c
> +++ b/drivers/usb/storage/transport.c
> @@ -416,7 +416,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
>
> /* don't submit s-g requests during abort processing */
> if (test_bit(US_FLIDX_ABORTING, &us->dflags))
> - return USB_STOR_XFER_ERROR;
> + goto usb_stor_xfer_error;
>
> /* initialize the scatter-gather request block */
> usb_stor_dbg(us, "xfer %u bytes, %d entries\n", length, num_sg);
> @@ -424,7 +424,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
> sg, num_sg, length, GFP_NOIO);
> if (result) {
> usb_stor_dbg(us, "usb_sg_init returned %d\n", result);
> - return USB_STOR_XFER_ERROR;
> + goto usb_stor_xfer_error;
> }
>
> /*
> @@ -452,6 +452,11 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
> *act_len = us->current_sg.bytes;
> return interpret_urb_result(us, pipe, length, result,
> us->current_sg.bytes);
> +
> +usb_stor_xfer_error:
> + if (act_len)
> + *act_len = 0;
> + return USB_STOR_XFER_ERROR;
> }
>
> /*

Acked-by: Alan Stern <[email protected]>

2020-11-12 20:15:12

by Nathan Chancellor

Subject: Re: [PATCH] USB: storage: avoid use of uninitialized values in error path

On Thu, Nov 12, 2020 at 08:12:55PM +0100, Lukas Bulwahn wrote:
> When usb_stor_bulk_transfer_sglist() returns with USB_STOR_XFER_ERROR, it
> returns without writing to its parameter *act_len.
>
> Further, the two callers of usb_stor_bulk_transfer_sglist():
>
> usb_stor_bulk_srb() and
> usb_stor_bulk_transfer_sg(),
>
> use the passed variable partial without checking the return value. Hence,
> the uninitialized value of partial is then used in the further execution
> of those two functions.
>
> Clang-analyzer detects this potential control and data flow and warns:
>
> drivers/usb/storage/transport.c:469:40:
> warning: The right operand of '-' is a garbage value
> [clang-analyzer-core.UndefinedBinaryOperatorResult]
> scsi_set_resid(srb, scsi_bufflen(srb) - partial);
> ^
>
> drivers/usb/storage/transport.c:495:15:
> warning: Assigned value is garbage or undefined
> [clang-analyzer-core.uninitialized.Assign]
> length_left -= partial;
> ^
>
> When a transfer error occurs, the *act_len value is probably ignored by the
> higher layers. But it won't hurt to set it to a valid number, just in case.
>
> For the two early-return paths in usb_stor_bulk_transfer_sglist(), the
> amount of data transferred is 0. So if act_len is not NULL, set *act_len
> to 0 in those paths. That makes clang-analyzer happy.
>
> Proposal was discussed in this mail thread:
>
> Link: https://lore.kernel.org/linux-usb/alpine.DEB.2.21.2011112146110.13119@felia/
>
> Signed-off-by: Lukas Bulwahn <[email protected]>

Assuming that setting it to zero is okay (sounds like it is based on the
other thread), this is a reasonable fix.

Reviewed-by: Nathan Chancellor <[email protected]>

> ---
> applies cleanly on current master and next-20201112
>
> I did some basic compile testing...
>
> Alan, Greg, please pick this minor non-urgent clean-up patch.
>
> drivers/usb/storage/transport.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
> index 238a8088e17f..5eb895b19c55 100644
> --- a/drivers/usb/storage/transport.c
> +++ b/drivers/usb/storage/transport.c
> @@ -416,7 +416,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
>
> /* don't submit s-g requests during abort processing */
> if (test_bit(US_FLIDX_ABORTING, &us->dflags))
> - return USB_STOR_XFER_ERROR;
> + goto usb_stor_xfer_error;
>
> /* initialize the scatter-gather request block */
> usb_stor_dbg(us, "xfer %u bytes, %d entries\n", length, num_sg);
> @@ -424,7 +424,7 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
> sg, num_sg, length, GFP_NOIO);
> if (result) {
> usb_stor_dbg(us, "usb_sg_init returned %d\n", result);
> - return USB_STOR_XFER_ERROR;
> + goto usb_stor_xfer_error;
> }
>
> /*
> @@ -452,6 +452,11 @@ static int usb_stor_bulk_transfer_sglist(struct us_data *us, unsigned int pipe,
> *act_len = us->current_sg.bytes;
> return interpret_urb_result(us, pipe, length, result,
> us->current_sg.bytes);
> +
> +usb_stor_xfer_error:
> + if (act_len)
> + *act_len = 0;
> + return USB_STOR_XFER_ERROR;
> }
>
> /*
> --
> 2.17.1
>