[PATCH v2 2/5] gpu: nova-core: use checked arithmetic in Booter signature parsing

[Joel Fernandes]

Use checked_add() when computing signature offsets from firmware-
provided values in signatures_iter().

Without checked arithmetic, overflow could wrap to a small plausible
offset that points to entirely wrong data.

Reviewed-by: Zhi Wang <zhiw at nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf at nvidia.com>
---
 drivers/gpu/nova-core/firmware/booter.rs | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/nova-core/firmware/booter.rs b/drivers/gpu/nova-core/firmware/booter.rs
index 86556cee8e67..40ac7e66d228 100644
--- a/drivers/gpu/nova-core/firmware/booter.rs
+++ b/drivers/gpu/nova-core/firmware/booter.rs
@@ -119,14 +119,23 @@ fn signatures_iter(&'a self) -> Result<impl Iterator<Item = BooterSignature<'a>>
             Some(sig_size) => {
                 let patch_sig =
                     frombytes_at::<u32>(self.fw, self.hdr.patch_sig_offset.into_safe_cast())?;
-                let signatures_start = usize::from_safe_cast(self.hdr.sig_prod_offset + patch_sig);
+
+                // Compute signatures_start = sig_prod_offset + patch_sig.
+                let signatures_start = self
+                    .hdr
+                    .sig_prod_offset
+                    .checked_add(patch_sig)
+                    .map(usize::from_safe_cast)
+                    .ok_or(EINVAL)?;
+
+                // Compute signatures_end = signatures_start + sig_prod_size.
+                let signatures_end = signatures_start
+                    .checked_add(usize::from_safe_cast(self.hdr.sig_prod_size))
+                    .ok_or(EINVAL)?;
 
                 self.fw
                     // Get signatures range.
-                    .get(
-                        signatures_start
-                            ..signatures_start + usize::from_safe_cast(self.hdr.sig_prod_size),
-                    )
+                    .get(signatures_start..signatures_end)
                     .ok_or(EINVAL)?
                     .chunks_exact(sig_size.into_safe_cast())
             }
-- 
2.34.1