[PATCH 1/1] fs/ntfs.c: Correct next_attribute validation

[Andrew Hamilton <adhamilt@gmail.com>]

Improved ad-hoc fuzzing coverage releaved a possible access violation
around line 342 of ntfs.c when accessing the attr_cur pointer due to
possiblity of moving pointer 'next' beyond of the end of the valid
buffer inside next_attribute. Prevent this for cases where full
attribute validation is not performed (such as on attribute lists)
by performing a sanity check on the newly calculated next pointer.

Fixes: 06914b614 (fs/ntfs: Correct attribute vs attribute list validation)

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
---
 grub-core/fs/ntfs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index 5b0a18f3d..9aff239c4 100644
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -233,7 +233,12 @@ next_attribute (grub_uint8_t *curr_attribute, void *end, bool validate)
     return NULL;
 
   next += u16at (curr_attribute, 4);
-  if (validate && validate_attribute (next, end) == false)
+  if (validate)
+  {
+    if (validate_attribute (next, end) == false)
+      return NULL;
+  }
+  else if (next >= (grub_uint8_t *)end)
     return NULL;
 
   return next;
-- 
2.39.5


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