Re: [PATCH bpf-next v2 1/3] bpf/verifier: Fix potential memory leak in array reallocation

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[ +Lorenz ]

On 10/31/22 9:16 PM, Bill Wendling wrote:
On Fri, Oct 28, 2022 at 7:55 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:

If an error (NULL) is returned by krealloc(), callers of realloc_array()
were setting their allocation pointers to NULL, but on error krealloc()
does not touch the original allocation. This would result in a memory
resource leak. Instead, free the old allocation on the error handling
path.

Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
Cc: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Bill Wendling <morbo@xxxxxxxxxx>

---
  kernel/bpf/verifier.c | 9 +++++++--
  1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 014ee0953dbd..eb8c34db74c7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1027,12 +1027,17 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t
   */
  static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
  {
+       void *new_arr;
+
         if (!new_n || old_n == new_n)
                 goto out;

-       arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
-       if (!arr)
+       new_arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
+       if (!new_arr) {
+               kfree(arr);
                 return NULL;
+       }
+       arr = new_arr;

Fyi, I took this fix into bpf tree and improved commit log a bit with the
one from Zhengchao [0] given yours came in first. Fixes tag would have been
nice, I added the c69431aab67a to the commit message while applying.

  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20221031070812.339883-1-shaozhengchao@xxxxxxxxxx/

         if (new_n > old_n)
                 memset(arr + old_n * size, 0, (new_n - old_n) * size);
--
2.34.1





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