[PATCH v6] nvme: reject passthrough of driver-managed Set Features

[Chao Shi <coshi036@gmail.com>]

Since commit b58da2d270db ("nvme: update keep alive interval when kato
is modified"), a Set Features (KATO) passthrough command lets userspace
start keep-alive on any transport. nvme_keep_alive_work() allocates with
BLK_MQ_REQ_RESERVED, but nvme_alloc_admin_tag_set() reserves admin tags
only for fabrics, so on other transports the allocation trips
WARN_ON_ONCE() in blk_mq_get_tag() and fails:

  nvme nvme0: keep-alive failed: -11

Several Set Features change controller state the driver manages itself
and cannot react to when set behind its back. Reject these in
nvme_admin_cmd_allowed():

  - KATO on non-fabrics (keep-alive is only armed for fabrics; on PCIe
    it has no reserved tag and harms idle power states)
  - Host Behavior Support, Host Memory Buffer, Number of Queues, and
    Autonomous Power State Transition (all driver-managed)

Keep Alive on fabrics is unchanged; I/O commands are unaffected as the
check is confined to the admin path (ns == NULL).

Link: https://lore.kernel.org/linux-nvme/20260523225629.3964037-1-coshi036@gmail.com/

Fixes: b58da2d270db ("nvme: update keep alive interval when kato is modified")

Found by FuzzNvme.

Acked-by: Sungwoo Kim <iam@sung-woo.kim>
Acked-by: Dave Tian <daveti@purdue.edu>
Acked-by: Weidong Zhu <weizhu@fiu.edu>
Signed-off-by: Chao Shi <coshi036@gmail.com>
---

Reproducer for the keep-alive case (run as root on a PCIe NVMe device):

    #include <fcntl.h>
    #include <stdio.h>
    #include <string.h>
    #include <sys/ioctl.h>
    #include <linux/nvme_ioctl.h>

    int main(void)
    {
            struct nvme_admin_cmd cmd = {0};
            int fd = open("/dev/nvme0", O_RDWR);
            if (fd < 0) { perror("open"); return 1; }
            cmd.opcode = 0x09;       /* SET_FEATURES */
            cmd.cdw10  = 0x0f;       /* Feature ID: KATO */
            cmd.cdw11  = 5;          /* KATO = 5 seconds */
            if (ioctl(fd, NVME_IOCTL_ADMIN_CMD, &cmd) < 0) {
                    perror("ioctl");
                    return 1;
            }
            return 0;
    }

On an unpatched kernel, within ~kato/2 seconds after the program exits,
dmesg shows:

    nvme nvme0: keep alive interval updated from 0 ms to 5000 ms
    WARNING: CPU: 0 PID: ... at block/blk-mq-tag.c:148 blk_mq_get_tag+...
    nvme nvme0: keep-alive failed: -11

With this patch the ioctl fails with EACCES on non-fabrics.

Changes since v5:
- Split nvme_cmd_allowed() into nvme_admin_cmd_allowed() and
  nvme_ns_cmd_allowed(), switch on the command, and fix the overly
  long lines (Christoph Hellwig).
 drivers/nvme/host/ioctl.c | 109 +++++++++++++++++++++++++-------------
 1 file changed, 71 insertions(+), 38 deletions(-)

diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index a9c097dacad6..ccd0120ad2e6 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -14,45 +14,54 @@ enum {
 	NVME_IOCTL_PARTITION	= (1 << 1),
 };
 
-static bool nvme_cmd_allowed(struct nvme_ns *ns, struct nvme_command *c,
-		unsigned int flags, bool open_for_write)
+static bool nvme_admin_cmd_allowed(struct nvme_ctrl *ctrl,
+				   struct nvme_command *c)
 {
-	u32 effects;
-
-	/*
-	 * Do not allow unprivileged passthrough on partitions, as that allows an
-	 * escape from the containment of the partition.
-	 */
-	if (flags & NVME_IOCTL_PARTITION)
-		goto admin;
-
-	/*
-	 * Do not allow unprivileged processes to send vendor specific or fabrics
-	 * commands as we can't be sure about their effects.
-	 */
-	if (c->common.opcode >= nvme_cmd_vendor_start ||
-	    c->common.opcode == nvme_fabrics_command)
-		goto admin;
-
 	/*
 	 * Do not allow unprivileged passthrough of admin commands except
 	 * for a subset of identify commands that contain information required
 	 * to form proper I/O commands in userspace and do not expose any
 	 * potentially sensitive information.
 	 */
-	if (!ns) {
-		if (c->common.opcode == nvme_admin_identify) {
-			switch (c->identify.cns) {
-			case NVME_ID_CNS_NS:
-			case NVME_ID_CNS_CS_NS:
-			case NVME_ID_CNS_NS_CS_INDEP:
-			case NVME_ID_CNS_CS_CTRL:
-			case NVME_ID_CNS_CTRL:
-				return true;
-			}
+	switch (c->common.opcode) {
+	case nvme_admin_identify:
+		switch (c->identify.cns) {
+		case NVME_ID_CNS_NS:
+		case NVME_ID_CNS_CS_NS:
+		case NVME_ID_CNS_NS_CS_INDEP:
+		case NVME_ID_CNS_CS_CTRL:
+		case NVME_ID_CNS_CTRL:
+			return true;
 		}
-		goto admin;
+		break;
+	case nvme_admin_set_features:
+		/*
+		 * Reject Set Features that change controller state the driver
+		 * manages itself; setting them behind the driver's back from
+		 * userspace leaves it unable to react correctly. Keep Alive is
+		 * only armed for fabrics - on other transports it has no
+		 * reserved tag and harms idle power states.
+		 */
+		switch (le32_to_cpu(c->features.fid) & 0xff) {
+		case NVME_FEAT_KATO:
+			if (ctrl->ops->flags & NVME_F_FABRICS)
+				break;
+			fallthrough;
+		case NVME_FEAT_HOST_BEHAVIOR:
+		case NVME_FEAT_HOST_MEM_BUF:
+		case NVME_FEAT_NUM_QUEUES:
+		case NVME_FEAT_AUTO_PST:
+			return false;
+		}
+		break;
 	}
+	return capable(CAP_SYS_ADMIN);
+}
+
+static bool nvme_ns_cmd_allowed(struct nvme_ns *ns, struct nvme_command *c,
+				bool open_for_write)
+{
+	u32 effects;
 
 	/*
 	 * Check if the controller provides a Commands Supported and Effects log
@@ -61,7 +70,7 @@ static bool nvme_cmd_allowed(struct nvme_ns *ns, struct nvme_command *c,
 	 */
 	effects = nvme_command_effects(ns->ctrl, ns, c->common.opcode);
 	if (!(effects & NVME_CMD_EFFECTS_CSUPP))
-		goto admin;
+		return capable(CAP_SYS_ADMIN);
 
 	/*
 	 * Don't allow passthrough for command that have intrusive (or unknown)
@@ -70,7 +79,7 @@ static bool nvme_cmd_allowed(struct nvme_ns *ns, struct nvme_command *c,
 	if (effects & ~(NVME_CMD_EFFECTS_CSUPP | NVME_CMD_EFFECTS_LBCC |
 			NVME_CMD_EFFECTS_UUID_SEL |
 			NVME_CMD_EFFECTS_SCOPE_MASK))
-		goto admin;
+		return capable(CAP_SYS_ADMIN);
 
 	/*
 	 * Only allow I/O commands that transfer data to the controller or that
@@ -79,11 +88,34 @@ static bool nvme_cmd_allowed(struct nvme_ns *ns, struct nvme_command *c,
 	 */
 	if ((nvme_is_write(c) || (effects & NVME_CMD_EFFECTS_LBCC)) &&
 	    !open_for_write)
-		goto admin;
+		return capable(CAP_SYS_ADMIN);
 
 	return true;
-admin:
-	return capable(CAP_SYS_ADMIN);
+}
+
+static bool nvme_cmd_allowed(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
+			     struct nvme_command *c, unsigned int flags,
+			     bool open_for_write)
+{
+	/*
+	 * Do not allow unprivileged passthrough on partitions, as that
+	 * allows an escape from the containment of the partition.
+	 */
+	if (flags & NVME_IOCTL_PARTITION)
+		return capable(CAP_SYS_ADMIN);
+
+	/*
+	 * Do not allow unprivileged processes to send vendor specific or
+	 * fabrics commands as we can't be sure about their effects.
+	 */
+	if (c->common.opcode >= nvme_cmd_vendor_start ||
+	    c->common.opcode == nvme_fabrics_command)
+		return capable(CAP_SYS_ADMIN);
+
+	if (!ns)
+		return nvme_admin_cmd_allowed(ctrl, c);
+
+	return nvme_ns_cmd_allowed(ns, c, open_for_write);
 }
 
 /*
@@ -308,7 +340,7 @@ static int nvme_user_cmd(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	c.common.cdw14 = cpu_to_le32(cmd.cdw14);
 	c.common.cdw15 = cpu_to_le32(cmd.cdw15);
 
-	if (!nvme_cmd_allowed(ns, &c, 0, open_for_write))
+	if (!nvme_cmd_allowed(ctrl, ns, &c, 0, open_for_write))
 		return -EACCES;
 
 	if (cmd.timeout_ms)
@@ -355,7 +387,7 @@ static int nvme_user_cmd64(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	c.common.cdw14 = cpu_to_le32(cmd.cdw14);
 	c.common.cdw15 = cpu_to_le32(cmd.cdw15);
 
-	if (!nvme_cmd_allowed(ns, &c, flags, open_for_write))
+	if (!nvme_cmd_allowed(ctrl, ns, &c, flags, open_for_write))
 		return -EACCES;
 
 	if (cmd.timeout_ms)
@@ -442,6 +474,7 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
 	const struct nvme_uring_cmd *cmd = io_uring_sqe_cmd(ioucmd->sqe);
 	struct request_queue *q = ns ? ns->queue : ctrl->admin_q;
+	bool open_for_write = ioucmd->file->f_mode & FMODE_WRITE;
 	struct nvme_uring_data d;
 	struct nvme_command c;
 	struct iov_iter iter;
@@ -472,7 +505,7 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	c.common.cdw14 = cpu_to_le32(READ_ONCE(cmd->cdw14));
 	c.common.cdw15 = cpu_to_le32(READ_ONCE(cmd->cdw15));
 
-	if (!nvme_cmd_allowed(ns, &c, 0, ioucmd->file->f_mode & FMODE_WRITE))
+	if (!nvme_cmd_allowed(ctrl, ns, &c, 0, open_for_write))
 		return -EACCES;
 
 	d.metadata = READ_ONCE(cmd->metadata);
-- 
2.43.0