[PATCH] bpf: Fix backport of "bpf: restrict unknown scalars of mixed signed bounds for unprivileged"

[PATCH] bpf: Fix backport of "bpf: restrict unknown scalars of mixed signed bounds for unprivileged"

[Samuel Mendoza-Jonas]

The 4.14 backport of 9d7eceede ("bpf: restrict unknown scalars of mixed
signed bounds for unprivileged") adds the PTR_TO_MAP_VALUE check to the
wrong location in adjust_ptr_min_max_vals(), most likely because 4.14
doesn't include the commit that updates the if-statement to a
switch-statement (aad2eeaf4 "bpf: Simplify ptr_min_max_vals adjustment").

Move the check to the proper location in adjust_ptr_min_max_vals().

Fixes: 17efa65350c5a ("bpf: restrict unknown scalars of mixed signed bounds for unprivileged")
Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
Reviewed-by: Frank van der Linden <fllinden@amazon.com>
Reviewed-by: Ethan Chen <yishache@amazon.com>
---
 kernel/bpf/verifier.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0c3a9302be93..9e9b7c076bcb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2204,6 +2204,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 				dst);
 		return -EACCES;
 	}
+	if (ptr_reg->type == PTR_TO_MAP_VALUE) {
+		if (!env->allow_ptr_leaks && !known && (smin_val < 0) != (smax_val < 0)) {
+			verbose("R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n",
+				off_reg == dst_reg ? dst : src);
+			return -EACCES;
+		}
+	}
 
 	/* In case of 'scalar += pointer', dst_reg inherits pointer type and id.
 	 * The id may be overwritten later if we create a new variable offset.
@@ -2349,13 +2356,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 			verbose("R%d bitwise operator %s on pointer prohibited\n",
 				dst, bpf_alu_string[opcode >> 4]);
 		return -EACCES;
-	case PTR_TO_MAP_VALUE:
-		if (!env->allow_ptr_leaks && !known && (smin_val < 0) != (smax_val < 0)) {
-			verbose("R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n",
-				off_reg == dst_reg ? dst : src);
-			return -EACCES;
-		}
-		/* fall-through */
 	default:
 		/* other operators (e.g. MUL,LSH) produce non-pointer results */
 		if (!env->allow_ptr_leaks)
-- 
2.17.1

Re: [PATCH] bpf: Fix backport of "bpf: restrict unknown scalars of mixed signed bounds for unprivileged"

[Yonghong Song]

On 4/19/21 4:56 PM, Samuel Mendoza-Jonas wrote:
> The 4.14 backport of 9d7eceede ("bpf: restrict unknown scalars of mixed
> signed bounds for unprivileged") adds the PTR_TO_MAP_VALUE check to the
> wrong location in adjust_ptr_min_max_vals(), most likely because 4.14
> doesn't include the commit that updates the if-statement to a
> switch-statement (aad2eeaf4 "bpf: Simplify ptr_min_max_vals adjustment").
> 
> Move the check to the proper location in adjust_ptr_min_max_vals().
> 
> Fixes: 17efa65350c5a ("bpf: restrict unknown scalars of mixed signed bounds for unprivileged")
> Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
> Reviewed-by: Frank van der Linden <fllinden@amazon.com>
> Reviewed-by: Ethan Chen <yishache@amazon.com>

Just to be clear, the patch is for 4.14 stable branch.

Acked-by: Yonghong Song <yhs@fb.com>

Re: [PATCH] bpf: Fix backport of "bpf: restrict unknown scalars of mixed signed bounds for unprivileged"

[Balbir Singh]

On Mon, Apr 19, 2021 at 04:56:41PM -0700, Samuel Mendoza-Jonas wrote:
> The 4.14 backport of 9d7eceede ("bpf: restrict unknown scalars of mixed
> signed bounds for unprivileged") adds the PTR_TO_MAP_VALUE check to the
> wrong location in adjust_ptr_min_max_vals(), most likely because 4.14
> doesn't include the commit that updates the if-statement to a
> switch-statement (aad2eeaf4 "bpf: Simplify ptr_min_max_vals adjustment").
> 
> Move the check to the proper location in adjust_ptr_min_max_vals().
> 
> Fixes: 17efa65350c5a ("bpf: restrict unknown scalars of mixed signed bounds for unprivileged")
> Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
> Reviewed-by: Frank van der Linden <fllinden@amazon.com>
> Reviewed-by: Ethan Chen <yishache@amazon.com>
> ---

Thanks for catching it :)

Reviewed-by: Balbir Singh <bsingharora@gmail.com>