leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

bpf: Disallow negative offset in check_ptr_off_reg

Browse Source 
check_ptr_off_reg only allows fixed offset to be set for PTR_TO_BTF_ID,
where reg->off < 0 doesn't make sense. This would shift the pointer
backwards, and fails later in btf_struct_ids_match or btf_struct_walk
due to out of bounds access (since offset is interpreted as unsigned).

Improve the verifier by rejecting this case by using a better error
message for BPF helpers and kfunc, by putting a check inside the
check_func_arg_reg_off function.

Also, update existing verifier selftests to work with new error string.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220304224645.3677453-4-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi
2022-03-05 04:16:40 +05:30
committed by Alexei Starovoitov
parent 655efe5089
commit e1fad0ff46
3 changed files with 11 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
kernel/bpf/verifier.c
View File

@@ -3990,6 +3990,12 @@ static int __check_ptr_off_reg(struct bpf_verifier_env *env,
* is only allowed in its original, unmodified form.
*/
if (reg->off < 0) {
verbose(env, "negative offset %s ptr R%d off=%d disallowed\n",
reg_type_str(env, reg->type), regno, reg->off);
return -EACCES;
}
if (!fixed_off_ok && reg->off) {
verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n",
reg_type_str(env, reg->type), regno, reg->off);