[PATCH] efi/efi_test: bound capsule_count to what the int loop index can hold

[Muhammad Bilal <meatuni001@gmail.com>]

efi_runtime_query_capsulecaps() only rejects capsule_count == ULONG_MAX
(to stop "capsule_count + 1" wrapping the kzalloc_objs() count to
zero), but then walks the array with
"for (i = 0; i < qcaps.capsule_count; i++)"
using a plain int i against an unsigned long bound. A capsule_count
between INT_MAX and ULONG_MAX - 1 lets i wrap through INT_MIN instead
of ever reaching the loop bound, and capsules[i] with a negative i
indexes before the allocation.

kzalloc_objs() would have to succeed at that size for the loop to be
reached at all, which bounds this in practice, but the check should
not rely on the allocator failing first. Reject any capsule_count
that would not fit in the int index up front.

Fixes: 092e72c9edab ("efi/efi_test: Prevent an Oops in efi_runtime_query_capsulecaps()")
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
 drivers/firmware/efi/test/efi_test.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/test/efi_test.c b/drivers/firmware/efi/test/efi_test.c
index d54d6a671326..683a0524dd31 100644
--- a/drivers/firmware/efi/test/efi_test.c
+++ b/drivers/firmware/efi/test/efi_test.c
@@ -611,7 +611,8 @@ static long efi_runtime_query_capsulecaps(unsigned long arg)
 	if (copy_from_user(&qcaps, qcaps_user, sizeof(qcaps)))
 		return -EFAULT;
 
-	if (qcaps.capsule_count == ULONG_MAX)
+	/* capsule_count is iterated over with a signed int index below */
+	if (qcaps.capsule_count >= INT_MAX)
 		return -EINVAL;
 
 	capsules = kzalloc_objs(efi_capsule_header_t, qcaps.capsule_count + 1);
-- 
2.55.0