[PATCH v2] ublk: validate physical_bs_shift, io_min_shift and io_opt_shift

[PATCH v2] ublk: validate physical_bs_shift, io_min_shift and io_opt_shift

[Ming Lei]

ublk_validate_params() checks logical_bs_shift is within
[9, PAGE_SHIFT] but has no upper bound for physical_bs_shift,
io_min_shift, or io_opt_shift. A malicious userspace can set any
of these to a large value (e.g., 44), causing undefined behavior
from `1 << shift` in ublk_ctrl_start_dev() since the result is
stored in 32-bit unsigned int.

Cap all three at ilog2(SZ_256M) (28). 256M is big enough to cover
all practical block sizes, and originates from the maximum physical
block size possible in NVMe (lba_size * (1 + npwg), where npwg is
16-bit).

Also zero out ub->params with memset() when copy_from_user() fails
or ublk_validate_params() returns error, so that no stale or partial
params survive for a subsequent START_DEV to consume.

Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
V2:
	- zero out ub->params in case of partial copy or validation failure

 drivers/block/ublk_drv.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index d10460d29e4a..57ec900f0ce0 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -900,6 +900,20 @@ static int ublk_validate_params(const struct ublk_device *ub)
 		if (p->logical_bs_shift > PAGE_SHIFT || p->logical_bs_shift < 9)
 			return -EINVAL;
 
+		/*
+		 * 256M is a reasonable upper bound for physical block size,
+		 * io_min and io_opt; it aligns with the maximum physical
+		 * block size possible in NVMe.
+		 */
+		if (p->physical_bs_shift > ilog2(SZ_256M))
+			return -EINVAL;
+
+		if (p->io_min_shift > ilog2(SZ_256M))
+			return -EINVAL;
+
+		if (p->io_opt_shift > ilog2(SZ_256M))
+			return -EINVAL;
+
 		if (p->logical_bs_shift > p->physical_bs_shift)
 			return -EINVAL;
 
@@ -4992,13 +5006,15 @@ static int ublk_ctrl_set_params(struct ublk_device *ub,
 		 */
 		ret = -EACCES;
 	} else if (copy_from_user(&ub->params, argp, ph.len)) {
+		/* zero out partial copy so no stale params survive */
+		memset(&ub->params, 0, sizeof(ub->params));
 		ret = -EFAULT;
 	} else {
 		/* clear all we don't support yet */
 		ub->params.types &= UBLK_PARAM_TYPE_ALL;
 		ret = ublk_validate_params(ub);
 		if (ret)
-			ub->params.types = 0;
+			memset(&ub->params, 0, sizeof(ub->params));
 	}
 	mutex_unlock(&ub->mutex);
 
-- 
2.53.0

Re: [PATCH v2] ublk: validate physical_bs_shift, io_min_shift and io_opt_shift

[Jens Axboe]

On Wed, 06 May 2026 16:22:38 +0800, Ming Lei wrote:
> ublk_validate_params() checks logical_bs_shift is within
> [9, PAGE_SHIFT] but has no upper bound for physical_bs_shift,
> io_min_shift, or io_opt_shift. A malicious userspace can set any
> of these to a large value (e.g., 44), causing undefined behavior
> from `1 << shift` in ublk_ctrl_start_dev() since the result is
> stored in 32-bit unsigned int.
> 
> [...]

Applied, thanks!

[1/1] ublk: validate physical_bs_shift, io_min_shift and io_opt_shift
      commit: 86f33ca9bea30cf011f2b1edad4593faea9c6e98

Best regards,
-- 
Jens Axboe