[PATCH 5.4.y] comedi: Fix initialization of data for instructions that write to subdevice

[PATCH 5.4.y] comedi: Fix initialization of data for instructions that write to subdevice

[Ian Abbott]

[ Upstream commit 46d8c744136ce2454aa4c35c138cc06817f92b8e ]

Some Comedi subdevice instruction handlers are known to access
instruction data elements beyond the first `insn->n` elements in some
cases.  The `do_insn_ioctl()` and `do_insnlist_ioctl()` functions
allocate at least `MIN_SAMPLES` (16) data elements to deal with this,
but they do not initialize all of that.  For Comedi instruction codes
that write to the subdevice, the first `insn->n` data elements are
copied from user-space, but the remaining elements are left
uninitialized.  That could be a problem if the subdevice instruction
handler reads the uninitialized data.  Ensure that the first
`MIN_SAMPLES` elements are initialized before calling these instruction
handlers, filling the uncopied elements with 0.  For
`do_insnlist_ioctl()`, the same data buffer elements are used for
handling a list of instructions, so ensure the first `MIN_SAMPLES`
elements are initialized for each instruction that writes to the
subdevice.

Fixes: ed9eccbe8970 ("Staging: add comedi core")
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250707161439.88385-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Reworked for before commit bac42fb21259 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CMD{,TEST} compat") ]
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
 drivers/staging/comedi/comedi_fops.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 413863bc929b..e4dfb5e7843d 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1544,7 +1544,7 @@ static int do_insnlist_ioctl(struct comedi_device *dev,
 	if (copy_from_user(&insnlist, arg, sizeof(insnlist)))
 		return -EFAULT;
 
-	ret = check_insnlist_len(dev, insnlist32.n_insns);
+	ret = check_insnlist_len(dev, insnlist.n_insns);
 	if (ret)
 		return ret;
 	insns = kcalloc(insnlist.n_insns, sizeof(*insns), GFP_KERNEL);
@@ -1580,21 +1580,27 @@ static int do_insnlist_ioctl(struct comedi_device *dev,
 	}
 
 	for (i = 0; i < insnlist.n_insns; ++i) {
+		unsigned int n = insns[i].n;
+
 		if (insns[i].insn & INSN_MASK_WRITE) {
 			if (copy_from_user(data, insns[i].data,
-					   insns[i].n * sizeof(unsigned int))) {
+					   n * sizeof(unsigned int))) {
 				dev_dbg(dev->class_dev,
 					"copy_from_user failed\n");
 				ret = -EFAULT;
 				goto error;
 			}
+			if (n < MIN_SAMPLES) {
+				memset(&data[n], 0, (MIN_SAMPLES - n) *
+						    sizeof(unsigned int));
+			}
 		}
 		ret = parse_insn(dev, insns + i, data, file);
 		if (ret < 0)
 			goto error;
 		if (insns[i].insn & INSN_MASK_READ) {
 			if (copy_to_user(insns[i].data, data,
-					 insns[i].n * sizeof(unsigned int))) {
+					 n * sizeof(unsigned int))) {
 				dev_dbg(dev->class_dev,
 					"copy_to_user failed\n");
 				ret = -EFAULT;
@@ -1661,6 +1667,10 @@ static int do_insn_ioctl(struct comedi_device *dev,
 			ret = -EFAULT;
 			goto error;
 		}
+		if (insn.n < MIN_SAMPLES) {
+			memset(&data[insn.n], 0,
+			       (MIN_SAMPLES - insn.n) * sizeof(unsigned int));
+		}
 	}
 	ret = parse_insn(dev, &insn, data, file);
 	if (ret < 0)
-- 
2.47.2

Re: [PATCH 5.4.y] comedi: Fix initialization of data for instructions that write to subdevice

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
❌ Patch application failures detected

The upstream commit SHA1 provided is correct: 46d8c744136ce2454aa4c35c138cc06817f92b8e

Status in newer kernel trees:
6.15.y | Not found
6.12.y | Not found
6.6.y | Not found
6.1.y | Not found
5.15.y | Not found
5.10.y | Not found

Note: Could not generate a diff with upstream commit:
---
Note: Could not generate diff - patch failed to apply for comparison
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| origin/linux-5.4.y        | Failed      | N/A        |

Re: [PATCH 5.4.y] comedi: Fix initialization of data for instructions that write to subdevice

[Ian Abbott]

On 26/07/2025 00:24, Sasha Levin wrote:
> [ Sasha's backport helper bot ]
> 
> Hi,
> 
> Summary of potential issues:
> ❌ Patch application failures detected
> 
> The upstream commit SHA1 provided is correct: 46d8c744136ce2454aa4c35c138cc06817f92b8e
> 
> Status in newer kernel trees:
> 6.15.y | Not found
> 6.12.y | Not found
> 6.6.y | Not found
> 6.1.y | Not found
> 5.15.y | Not found
> 5.10.y | Not found
> 
> Note: Could not generate a diff with upstream commit:
> ---
> Note: Could not generate diff - patch failed to apply for comparison
> ---
> 
> Results of testing on various branches:
> 
> | Branch                    | Patch Apply | Build Test |
> |---------------------------|-------------|------------|
> | origin/linux-5.4.y        | Failed      | N/A        |

Sorry about that. I was building a list of patches at the same time and 
applied a fixup to the wrong one.

-- 
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company  )=-
-=( registered in England & Wales.  Regd. number: 02862268.  )=-
-=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=-
-=( Bird Hall Lane, STOCKPORT, SK3 0XA, UK. || www.mev.co.uk )=-

[PATCH v2 5.4] comedi: Fix initialization of data for instructions that write to subdevice

[Ian Abbott]

[ Upstream commit 46d8c744136ce2454aa4c35c138cc06817f92b8e ]

Some Comedi subdevice instruction handlers are known to access
instruction data elements beyond the first `insn->n` elements in some
cases.  The `do_insn_ioctl()` and `do_insnlist_ioctl()` functions
allocate at least `MIN_SAMPLES` (16) data elements to deal with this,
but they do not initialize all of that.  For Comedi instruction codes
that write to the subdevice, the first `insn->n` data elements are
copied from user-space, but the remaining elements are left
uninitialized.  That could be a problem if the subdevice instruction
handler reads the uninitialized data.  Ensure that the first
`MIN_SAMPLES` elements are initialized before calling these instruction
handlers, filling the uncopied elements with 0.  For
`do_insnlist_ioctl()`, the same data buffer elements are used for
handling a list of instructions, so ensure the first `MIN_SAMPLES`
elements are initialized for each instruction that writes to the
subdevice.

Fixes: ed9eccbe8970 ("Staging: add comedi core")
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250707161439.88385-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Reworked for before commit bac42fb21259 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CMD{,TEST} compat") ]
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
v2: Fixed a patch application error due to fixing up the wrong commit.
---
 drivers/staging/comedi/comedi_fops.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 45e868badee4..e4dfb5e7843d 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1580,21 +1580,27 @@ static int do_insnlist_ioctl(struct comedi_device *dev,
 	}
 
 	for (i = 0; i < insnlist.n_insns; ++i) {
+		unsigned int n = insns[i].n;
+
 		if (insns[i].insn & INSN_MASK_WRITE) {
 			if (copy_from_user(data, insns[i].data,
-					   insns[i].n * sizeof(unsigned int))) {
+					   n * sizeof(unsigned int))) {
 				dev_dbg(dev->class_dev,
 					"copy_from_user failed\n");
 				ret = -EFAULT;
 				goto error;
 			}
+			if (n < MIN_SAMPLES) {
+				memset(&data[n], 0, (MIN_SAMPLES - n) *
+						    sizeof(unsigned int));
+			}
 		}
 		ret = parse_insn(dev, insns + i, data, file);
 		if (ret < 0)
 			goto error;
 		if (insns[i].insn & INSN_MASK_READ) {
 			if (copy_to_user(insns[i].data, data,
-					 insns[i].n * sizeof(unsigned int))) {
+					 n * sizeof(unsigned int))) {
 				dev_dbg(dev->class_dev,
 					"copy_to_user failed\n");
 				ret = -EFAULT;
@@ -1661,6 +1667,10 @@ static int do_insn_ioctl(struct comedi_device *dev,
 			ret = -EFAULT;
 			goto error;
 		}
+		if (insn.n < MIN_SAMPLES) {
+			memset(&data[insn.n], 0,
+			       (MIN_SAMPLES - insn.n) * sizeof(unsigned int));
+		}
 	}
 	ret = parse_insn(dev, &insn, data, file);
 	if (ret < 0)
-- 
2.47.2

Re: [PATCH v2 5.4] comedi: Fix initialization of data for instructions that write to subdevice

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 46d8c744136ce2454aa4c35c138cc06817f92b8e

Status in newer kernel trees:
6.15.y | Not found
6.12.y | Not found
6.6.y | Not found
6.1.y | Not found
5.15.y | Not found
5.10.y | Not found

Note: The patch differs from the upstream commit:
---
1:  46d8c744136c ! 1:  8293aa18dbe9 comedi: Fix initialization of data for instructions that write to subdevice
    @@ Metadata
      ## Commit message ##
         comedi: Fix initialization of data for instructions that write to subdevice
     
    +    [ Upstream commit 46d8c744136ce2454aa4c35c138cc06817f92b8e ]
    +
         Some Comedi subdevice instruction handlers are known to access
         instruction data elements beyond the first `insn->n` elements in some
         cases.  The `do_insn_ioctl()` and `do_insnlist_ioctl()` functions
    @@ Commit message
         Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
         Link: https://lore.kernel.org/r/20250707161439.88385-1-abbotti@mev.co.uk
         Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    +    [ Reworked for before commit bac42fb21259 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CMD{,TEST} compat") ]
    +    Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
     
    - ## drivers/comedi/comedi_fops.c ##
    -@@ drivers/comedi/comedi_fops.c: static int do_insnlist_ioctl(struct comedi_device *dev,
    + ## drivers/staging/comedi/comedi_fops.c ##
    +@@ drivers/staging/comedi/comedi_fops.c: static int do_insnlist_ioctl(struct comedi_device *dev,
      	}
      
    - 	for (i = 0; i < n_insns; ++i) {
    + 	for (i = 0; i < insnlist.n_insns; ++i) {
     +		unsigned int n = insns[i].n;
     +
      		if (insns[i].insn & INSN_MASK_WRITE) {
    @@ drivers/comedi/comedi_fops.c: static int do_insnlist_ioctl(struct comedi_device
      				dev_dbg(dev->class_dev,
      					"copy_to_user failed\n");
      				ret = -EFAULT;
    -@@ drivers/comedi/comedi_fops.c: static int do_insn_ioctl(struct comedi_device *dev,
    +@@ drivers/staging/comedi/comedi_fops.c: static int do_insn_ioctl(struct comedi_device *dev,
      			ret = -EFAULT;
      			goto error;
      		}
    -+		if (insn->n < MIN_SAMPLES) {
    -+			memset(&data[insn->n], 0,
    -+			       (MIN_SAMPLES - insn->n) * sizeof(unsigned int));
    ++		if (insn.n < MIN_SAMPLES) {
    ++			memset(&data[insn.n], 0,
    ++			       (MIN_SAMPLES - insn.n) * sizeof(unsigned int));
     +		}
      	}
    - 	ret = parse_insn(dev, insn, data, file);
    + 	ret = parse_insn(dev, &insn, data, file);
      	if (ret < 0)

---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| origin/linux-5.4.y        | Success     | Success    |