gpu: nova-core: fix bounds check in PmuLookupTableEntry::new

data is sliced from 2..6, but the bounds check data.len() < 5 does not satisfy those bounds.

---
Changes in v2:
- Ensure commit description does not spill into commit message
- Fix author to match SoB
- Add "Fixes:" tag
- Add base commit

---
 drivers/gpu/nova-core/vbios.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 663fc50e8b66..5b5d9f38cbb3 100644
@@ -901,7 +901,7 @@ struct PmuLookupTableEntry {
 
 impl PmuLookupTableEntry {
     fn new(data: &[u8]) -> Result<Self> {
-        if data.len() < 5 {
+        if data.len() < 6 {
             return Err(EINVAL);
         }
 

base-commit: 215a3f91713383a3c0d2da82d223a608a3c17ac1

2.50.1

Introduce an associated constant MIN_LEN for each struct that checks the length of the input data in its constructor against a magic number.

---
Changes in v2:
- Add commit description
- Fix author to match SoB
- Add base commit

---
 drivers/gpu/nova-core/vbios.rs | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

index 5b5d9f38cbb3..d456c494374d 100644
@@ -364,8 +364,9 @@ struct BitHeader {
 }
 
 impl BitHeader {
+    const MIN_LEN: usize = 12;
     fn new(data: &[u8]) -> Result<Self> {
-        if data.len() < 12 {
+        if data.len() < Self::MIN_LEN {
             return Err(EINVAL);
         }
 

@@ -467,8 +468,9 @@ struct PciRomHeader {
 }
 
 impl PciRomHeader {
+    const MIN_LEN: usize = 26;
     fn new(pdev: &pci::Device, data: &[u8]) -> Result<Self> {
-        if data.len() < 26 {
+        if data.len() < Self::MIN_LEN {
             // Need at least 26 bytes to read pciDataStrucPtr and sizeOfBlock.
             return Err(EINVAL);
         }

@@ -772,10 +774,11 @@ fn into_image(self) -> Result<BiosImage> {
         BiosImage::try_from(self)
     }
 
+    const MIN_LEN: usize = 26;
     /// Creates a new BiosImageBase from raw byte data.
     fn new(pdev: &pci::Device, data: &[u8]) -> Result<Self> {
         // Ensure we have enough data for the ROM header.
-        if data.len() < 26 {
+        if data.len() < Self::MIN_LEN {
             dev_err!(pdev.as_ref(), "Not enough data for ROM header\n");
             return Err(EINVAL);
         }

@@ -900,8 +903,9 @@ struct PmuLookupTableEntry {
 }
 
 impl PmuLookupTableEntry {
+    const MIN_LEN: usize = 6;
     fn new(data: &[u8]) -> Result<Self> {
-        if data.len() < 6 {
+        if data.len() < Self::MIN_LEN {
             return Err(EINVAL);
         }
 

@@ -928,8 +932,9 @@ struct PmuLookupTable {
 }
 
 impl PmuLookupTable {
+    const MIN_LEN: usize = 4;
     fn new(pdev: &pci::Device, data: &[u8]) -> Result<Self> {
-        if data.len() < 4 {
+        if data.len() < Self::MIN_LEN {
             return Err(EINVAL);
         }
 

base-commit: 215a3f91713383a3c0d2da82d223a608a3c17ac1
prerequisite-patch-id: d80f92d314a0693d4c89ffb7810d9ab6990336fa

2.50.1

As I mentioned in [1], I think this would be better addressed by working in terms of sizeof upon the relevant structures, after making them #[repr(C)]. It might require splitting them a bit since some contain other data (or we can maybe turn them into DSTs).

[1] https://lore.kernel.org/rust-for-linux/[email protected]/

As far as I can tell, only one of the five structs with MIN_LEN have the same layout in-memory as they do in the data byte slice, that being BitHeader.  Perhaps #[repr(packed)] could be used for PmuLookupTableEntry, sacrificing alignment, but that is undesirable as it comes with its own footguns such as unaligned loads.  The other structs include optional values and vectors which do not have the same encoding when reading from the data byte slice as they do in memory.  I have worked with DSTs before, but I don't recommend them for non-library code since they are not first-class citizens in Rust.  Notably the fat pointer is not resized when taking a reference to the unsized struct field, and constructing such objects is cumbersome.  Also, in the current version of Rust (1.88), DSTs cannot yet live comfortably on the stack.

This patch can be dropped if it's not valuable enough to warrant the change, I only made it because of your comment here: https://gitlab.freedesktop.org/drm/nova/-/merge_requests/4#note_2999761

Since this is a v2, the message subject should have read "[PATCH v2]". You can achieve this by passing -v 2 to git format-patch.

No need to resend, just pointing it out for next time. :)

For the fix in itself,

Applied to nova-next, thanks!