[PATCH v2] acpi: nfit: vmalloc-out-of-bounds Read in acpi_nfit_ctl

[Suraj Sonawane]

Fix an issue detected by syzbot with KASAN:

BUG: KASAN: vmalloc-out-of-bounds in cmd_to_func drivers/acpi/nfit/
core.c:416 [inline]
BUG: KASAN: vmalloc-out-of-bounds in acpi_nfit_ctl+0x20e8/0x24a0
drivers/acpi/nfit/core.c:459

The issue occurs in `cmd_to_func` when the `call_pkg->nd_reserved2`
array is accessed without verifying that `call_pkg` points to a
buffer that is sized appropriately as a `struct nd_cmd_pkg`. This
could lead to out-of-bounds access and undefined behavior if the
buffer does not have sufficient space.

To address this issue, a check was added in `acpi_nfit_ctl()` to
ensure that `buf` is not `NULL` and `buf_len` is greater than or
equal to `sizeof(struct nd_cmd_pkg)` before casting `buf` to
`struct nd_cmd_pkg *`. This ensures safe access to the members of
`call_pkg`, including the `nd_reserved2` array.

This change preventing out-of-bounds reads.

Reported-by: syzbot+7534f060ebda6b8b51b3@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=7534f060ebda6b8b51b3
Tested-by: syzbot+7534f060ebda6b8b51b3@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 2d5404caa8c7 ("Linux 6.12-rc7")
Signed-off-by: Suraj Sonawane <surajsonawane0215@xxxxxxxxx>
---
V1: https://lore.kernel.org/lkml/20241111080429.9861-1-surajsonawane0215@xxxxxxxxx/ 
V2: Initialized `out_obj` to `NULL` in `acpi_nfit_ctl()` to prevent
potential uninitialized variable usage if condition is true.

 drivers/acpi/nfit/core.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 5429ec9ef..d0e655a9c 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -439,7 +439,7 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
 {
 	struct acpi_nfit_desc *acpi_desc = to_acpi_desc(nd_desc);
 	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
-	union acpi_object in_obj, in_buf, *out_obj;
+	union acpi_object in_obj, in_buf, *out_obj = NULL;
 	const struct nd_cmd_desc *desc = NULL;
 	struct device *dev = acpi_desc->dev;
 	struct nd_cmd_pkg *call_pkg = NULL;
@@ -454,8 +454,14 @@ int acpi_nfit_ctl(struct nvdimm_bus_descriptor *nd_desc, struct nvdimm *nvdimm,
 	if (cmd_rc)
 		*cmd_rc = -EINVAL;
 
-	if (cmd == ND_CMD_CALL)
-		call_pkg = buf;
+	if (cmd == ND_CMD_CALL) {
+		if (buf == NULL || buf_len < sizeof(struct nd_cmd_pkg)) {
+			rc = -EINVAL;
+			goto out;
+		}
+		call_pkg = (struct nd_cmd_pkg *)buf;
+	}
+
 	func = cmd_to_func(nfit_mem, cmd, call_pkg, &family);
 	if (func < 0)
 		return func;
-- 
2.34.1