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loader/i386/bsd: Use safe math to avoid underflow

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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>
This commit is contained in:
Alec Brown authored and Daniel Kiper committed 2025-02-13 15:45:58 +01:00
1 parent 490a6ab71c
commit 4dc6166571
1 file changed
+10 -4
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grub-core/loader/i386/bsd.c
+10 -4
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@@ -1340,6 +1340,7 @@ static grub_err_t
grub_bsd_load_elf (grub_elf_t elf, const char *filename) grub_bsd_load_elf (grub_elf_t elf, const char *filename)
{ {
grub_err_t err; grub_err_t err;
grub_size_t sz;
kern_end = 0; kern_end = 0;
kern_start = ~0; kern_start = ~0;
@@ -1370,8 +1371,11 @@ grub_bsd_load_elf (grub_elf_t elf, const char *filename)
if (grub_errno) if (grub_errno)
return 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) if (err)
return err; return err;
@@ -1431,8 +1435,10 @@ grub_bsd_load_elf (grub_elf_t elf, const char *filename)
{ {
grub_relocator_chunk_t ch; grub_relocator_chunk_t ch;
err = grub_relocator_alloc_chunk_addr (relocator, &ch, kern_start, if (grub_sub (kern_end, kern_start, &sz))
kern_end - kern_start); 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) if (err)
return err; return err;
kern_chunk_src = get_virtual_current_address (ch); kern_chunk_src = get_virtual_current_address (ch);