[PATCH 5.4.y] comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[PATCH 5.4.y] comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[Ian Abbott]

[ Upstream commit 08ae4b20f5e82101d77326ecab9089e110f224cc ]

The handling of the `COMEDI_INSNLIST` ioctl allocates a kernel buffer to
hold the array of `struct comedi_insn`, getting the length from the
`n_insns` member of the `struct comedi_insnlist` supplied by the user.
The allocation will fail with a WARNING and a stack dump if it is too
large.

Avoid that by failing with an `-EINVAL` error if the supplied `n_insns`
value is unreasonable.

Define the limit on the `n_insns` value in the `MAX_INSNS` macro.  Set
this to the same value as `MAX_SAMPLES` (65536), which is the maximum
allowed sum of the values of the member `n` in the array of `struct
comedi_insn`, and sensible comedi instructions will have an `n` of at
least 1.

Reported-by: syzbot+d6995b62e5ac7d79557a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d6995b62e5ac7d79557a
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Tested-by: Ian Abbott <abbotti@mev.co.uk>
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250704120405.83028-1-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_compat32.c |  3 +++
 drivers/staging/comedi/comedi_fops.c     | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
index 36a3564ba1fb..2f444e2b92c2 100644
--- a/drivers/staging/comedi/comedi_compat32.c
+++ b/drivers/staging/comedi/comedi_compat32.c
@@ -360,6 +360,9 @@ static int compat_insnlist(struct file *file, unsigned long arg)
 	if (err)
 		return -EFAULT;
 
+	if (n_insns > 65536)	/* See MAX_INSNS in comedi_fops.c */
+		return -EINVAL;
+
 	/* Allocate user memory to copy insnlist and insns into. */
 	s = compat_alloc_user_space(offsetof(struct combined_insnlist,
 					     insn[n_insns]));
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 8b2337f8303d..413863bc929b 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1502,6 +1502,16 @@ static int parse_insn(struct comedi_device *dev, struct comedi_insn *insn,
 	return ret;
 }
 
+#define MAX_INSNS   65536
+static int check_insnlist_len(struct comedi_device *dev, unsigned int n_insns)
+{
+	if (n_insns > MAX_INSNS) {
+		dev_dbg(dev->class_dev, "insnlist length too large\n");
+		return -EINVAL;
+	}
+	return 0;
+}
+
 /*
  * COMEDI_INSNLIST ioctl
  * synchronous instruction list
@@ -1534,6 +1544,9 @@ 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);
+	if (ret)
+		return ret;
 	insns = kcalloc(insnlist.n_insns, sizeof(*insns), GFP_KERNEL);
 	if (!insns) {
 		ret = -ENOMEM;
-- 
2.47.2

Re: [PATCH 5.4.y] comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
❌ Build failures detected

The upstream commit SHA1 provided is correct: 08ae4b20f5e82101d77326ecab9089e110f224cc

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:  08ae4b20f5e8 < -:  ------------ comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large
-:  ------------ > 1:  480e150b6535 comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

---

Results of testing on various branches:

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

Build Errors:
origin/linux-5.4.y:
    Build error: Building current HEAD with log output
    Build x86: exited with code 2
    Cleaning up worktrees...
    Cleaning up worktrees...
    Cleaning up worktrees...
    Cleaning up worktrees...

Re: [PATCH 5.4.y] comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[Ian Abbott]

On 26/07/2025 00:26, Sasha Levin wrote:
> [ Sasha's backport helper bot ]
> 
> Hi,
> 
> Summary of potential issues:
> ❌ Build failures detected
> 
> The upstream commit SHA1 provided is correct: 08ae4b20f5e82101d77326ecab9089e110f224cc
> 
> 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:  08ae4b20f5e8 < -:  ------------ comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large
> -:  ------------ > 1:  480e150b6535 comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large
> 
> ---
> 
> Results of testing on various branches:
> 
> | Branch                    | Patch Apply | Build Test |
> |---------------------------|-------------|------------|
> | origin/linux-5.4.y        | Success     | Failed     |
> 
> Build Errors:
> origin/linux-5.4.y:
>      Build error: Building current HEAD with log output
>      Build x86: exited with code 2
>      Cleaning up worktrees...
>      Cleaning up worktrees...
>      Cleaning up worktrees...
>      Cleaning up worktrees...
> 

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: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[Ian Abbott]

[ Upstream commit 08ae4b20f5e82101d77326ecab9089e110f224cc ]

The handling of the `COMEDI_INSNLIST` ioctl allocates a kernel buffer to
hold the array of `struct comedi_insn`, getting the length from the
`n_insns` member of the `struct comedi_insnlist` supplied by the user.
The allocation will fail with a WARNING and a stack dump if it is too
large.

Avoid that by failing with an `-EINVAL` error if the supplied `n_insns`
value is unreasonable.

Define the limit on the `n_insns` value in the `MAX_INSNS` macro.  Set
this to the same value as `MAX_SAMPLES` (65536), which is the maximum
allowed sum of the values of the member `n` in the array of `struct
comedi_insn`, and sensible comedi instructions will have an `n` of at
least 1.

Reported-by: syzbot+d6995b62e5ac7d79557a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d6995b62e5ac7d79557a
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Tested-by: Ian Abbott <abbotti@mev.co.uk>
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250704120405.83028-1-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 build error due to applying a fixup to the wrong commit.
---
 drivers/staging/comedi/comedi_compat32.c |  3 +++
 drivers/staging/comedi/comedi_fops.c     | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
index 36a3564ba1fb..2f444e2b92c2 100644
--- a/drivers/staging/comedi/comedi_compat32.c
+++ b/drivers/staging/comedi/comedi_compat32.c
@@ -360,6 +360,9 @@ static int compat_insnlist(struct file *file, unsigned long arg)
 	if (err)
 		return -EFAULT;
 
+	if (n_insns > 65536)	/* See MAX_INSNS in comedi_fops.c */
+		return -EINVAL;
+
 	/* Allocate user memory to copy insnlist and insns into. */
 	s = compat_alloc_user_space(offsetof(struct combined_insnlist,
 					     insn[n_insns]));
diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 8b2337f8303d..45e868badee4 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1502,6 +1502,16 @@ static int parse_insn(struct comedi_device *dev, struct comedi_insn *insn,
 	return ret;
 }
 
+#define MAX_INSNS   65536
+static int check_insnlist_len(struct comedi_device *dev, unsigned int n_insns)
+{
+	if (n_insns > MAX_INSNS) {
+		dev_dbg(dev->class_dev, "insnlist length too large\n");
+		return -EINVAL;
+	}
+	return 0;
+}
+
 /*
  * COMEDI_INSNLIST ioctl
  * synchronous instruction list
@@ -1534,6 +1544,9 @@ static int do_insnlist_ioctl(struct comedi_device *dev,
 	if (copy_from_user(&insnlist, arg, sizeof(insnlist)))
 		return -EFAULT;
 
+	ret = check_insnlist_len(dev, insnlist.n_insns);
+	if (ret)
+		return ret;
 	insns = kcalloc(insnlist.n_insns, sizeof(*insns), GFP_KERNEL);
 	if (!insns) {
 		ret = -ENOMEM;
-- 
2.47.2

Re: [PATCH v2 5.4] comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

[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: 08ae4b20f5e82101d77326ecab9089e110f224cc

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:  08ae4b20f5e8 < -:  ------------ comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large
-:  ------------ > 1:  35bddb9d95d3 comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

---

Results of testing on various branches:

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