Re: [PATCH] ACPI: pfr_update: fix stack buffer overflow in query_capability()

> If the firmware wants the kernel to copy more data than the latter has
> room for, the operation should fail instead of pretending to succeed.

Agreed. v2 validates all four buffer lengths upfront and returns
-EINVAL if any exceeds its destination field size.

---

query_capability() copies four ACPI buffer objects returned by the
firmware _DSM into fixed-size u8[16] fields in struct
pfru_update_cap_info using memcpy with the firmware-supplied length:

  memcpy(&cap_hdr->code_type,
         elements[CAP_CODE_TYPE_IDX].buffer.pointer,
         elements[CAP_CODE_TYPE_IDX].buffer.length);

The same pattern repeats for drv_type, platform_id, and oem_id.
If the firmware returns buffer.length > 16 for any of these fields,
memcpy writes past the destination array.

struct pfru_update_cap_info is stack-allocated in pfru_ioctl().
Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports
are generated when a DSM returns 64-byte buffers, with writes reaching
44 bytes past the end of cap_hdr's [64, 156) frame window into
adjacent stack redzones.

Fix by validating each buffer length against its destination field
size before copying, and returning -EINVAL if the firmware supplies
an oversized buffer.

Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver")
Cc: [email protected]
Signed-off-by: Anirudh Prasad <[email protected]>
---
 drivers/acpi/pfr_update.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
index 6283105bb0e8..e14e053cea44 100644
--- a/drivers/acpi/pfr_update.c
+++ b/drivers/acpi/pfr_update.c
@@ -158,6 +158,14 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
 		goto free_acpi_buffer;
 	}
 
+	if (out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length > sizeof(cap_hdr->code_type) ||
+	    out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length > sizeof(cap_hdr->drv_type) ||
+	    out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length > sizeof(cap_hdr->platform_id) ||
+	    out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length > sizeof(cap_hdr->oem_id)) {
+		ret = -EINVAL;
+		goto free_acpi_buffer;
+	}
+
 	cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value;
 	memcpy(&cap_hdr->code_type,
 	       out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer,
-- 
2.55.0





From: Anirudh Prasad <[email protected]>
To: "linux-acpi"<[email protected]>
Cc: "rafaeljwysocki"<[email protected]>, "linux-kernel"<[email protected]>, "stable"<[email protected]>
Date: Thu, 06 Aug 2026 19:10:59 +0530
Subject: [PATCH] ACPI: pfr_update: fix stack buffer overflow in query_capability()

 > query_capability() copies four ACPI buffer objects returned by the 
 > firmware _DSM into fixed-size u8[16] fields in struct 
 > pfru_update_cap_info using memcpy with the firmware-supplied length: 
 >  
 >  memcpy(&cap_hdr->code_type, 
 >  elements[CAP_CODE_TYPE_IDX].buffer.pointer, 
 >  elements[CAP_CODE_TYPE_IDX].buffer.length); 
 >  
 > The same pattern repeats for drv_type, platform_id, and oem_id. 
 > If the firmware returns buffer.length > 16 for any of these fields, 
 > memcpy writes past the destination array. 
 >  
 > struct pfru_update_cap_info is stack-allocated in pfru_ioctl(). 
 > Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports 
 > are generated when a DSM returns 64-byte buffers, with writes reaching 
 > 44 bytes past the end of cap_hdr's [64, 156) frame window into 
 > adjacent stack redzones. 
 >  
 > Fix by clamping each memcpy length to the size of its destination 
 > field with min_t(u32, buffer.length, sizeof(cap_hdr->field)). 
 >  
 > Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver") 
 > Cc: [email protected] 
 > Signed-off-by: Anirudh Prasad <[email protected]> 
 > --- 
 >  drivers/acpi/pfr_update.c | 12 ++++++++---- 
 >  1 file changed, 8 insertions(+), 4 deletions(-) 
 >  
 > diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c 
 > index 6283105bb0e8..0219347cd78f 100644 
 > --- a/drivers/acpi/pfr_update.c 
 > +++ b/drivers/acpi/pfr_update.c 
 > @@ -161,24 +161,28 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr, 
 >      cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value; 
 >      memcpy(&cap_hdr->code_type, 
 >             out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer, 
 > -           out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length); 
 > +           min_t(u32, out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length, 
 > +             sizeof(cap_hdr->code_type))); 
 >      cap_hdr->fw_version = 
 >          out_obj->package.elements[CAP_FW_VER_IDX].integer.value; 
 >      cap_hdr->code_rt_version = 
 >          out_obj->package.elements[CAP_CODE_RT_VER_IDX].integer.value; 
 >      memcpy(&cap_hdr->drv_type, 
 >             out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.pointer, 
 > -           out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length); 
 > +           min_t(u32, out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length, 
 > +             sizeof(cap_hdr->drv_type))); 
 >      cap_hdr->drv_rt_version = 
 >          out_obj->package.elements[CAP_DRV_RT_VER_IDX].integer.value; 
 >      cap_hdr->drv_svn = 
 >          out_obj->package.elements[CAP_DRV_SVN_IDX].integer.value; 
 >      memcpy(&cap_hdr->platform_id, 
 >             out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.pointer, 
 > -           out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length); 
 > +           min_t(u32, out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length, 
 > +             sizeof(cap_hdr->platform_id))); 
 >      memcpy(&cap_hdr->oem_id, 
 >             out_obj->package.elements[CAP_OEM_ID_IDX].buffer.pointer, 
 > -           out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length); 
 > +           min_t(u32, out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length, 
 > +             sizeof(cap_hdr->oem_id))); 
 >      cap_hdr->oem_info_len = 
 >          out_obj->package.elements[CAP_OEM_INFO_IDX].buffer.length; 
 >  
 > -- 
 > 2.55.0 
 >