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

Samuel Mendoza-Jonas
2021-04-19T23:57:38Z

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