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From: Alec Brown <alec.r.brown@oracle.com>
Date: Wed, 5 Feb 2025 22:04:08 +0000
Subject: loader/i386/bsd: Use safe math to avoid underflow
The operation kern_end - kern_start may underflow when we input it into
grub_relocator_alloc_chunk_addr() call. To avoid this we can use safe
math for this subtraction.
Fixes: CID 73845
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/loader/i386/bsd.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/grub-core/loader/i386/bsd.c b/grub-core/loader/i386/bsd.c
index 1f9128f..5784334 100644
--- a/grub-core/loader/i386/bsd.c
+++ b/grub-core/loader/i386/bsd.c
@@ -1340,6 +1340,7 @@ static grub_err_t
grub_bsd_load_elf (grub_elf_t elf, const char *filename)
{
grub_err_t err;
+ grub_size_t sz;
kern_end = 0;
kern_start = ~0;
@@ -1370,8 +1371,11 @@ grub_bsd_load_elf (grub_elf_t elf, const char *filename)
if (grub_errno)
return grub_errno;
- err = grub_relocator_alloc_chunk_addr (relocator, &ch,
- kern_start, kern_end - kern_start);
+
+ if (grub_sub (kern_end, kern_start, &sz))
+ return grub_error (GRUB_ERR_OUT_OF_RANGE, "underflow detected while determining size of kernel for relocator");
+
+ err = grub_relocator_alloc_chunk_addr (relocator, &ch, kern_start, sz);
if (err)
return err;
@@ -1431,8 +1435,10 @@ grub_bsd_load_elf (grub_elf_t elf, const char *filename)
{
grub_relocator_chunk_t ch;
- err = grub_relocator_alloc_chunk_addr (relocator, &ch, kern_start,
- kern_end - kern_start);
+ if (grub_sub (kern_end, kern_start, &sz))
+ return grub_error (GRUB_ERR_OUT_OF_RANGE, "underflow detected while determining size of kernel for relocator");
+
+ err = grub_relocator_alloc_chunk_addr (relocator, &ch, kern_start, sz);
if (err)
return err;
kern_chunk_src = get_virtual_current_address (ch);
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