Fix crash when calling openat with sandbox enabled #25440

The seccomp rule for the openat syscall checks for the AT_FDCWD
constant. Because this constant is usually a negative value, a
cast to unsigned int is necessary to make sure it does not get
converted to uint64_t used by seccomp.

More info on:
https://github.com/seccomp/libseccomp/issues/69#issuecomment-273805980

diff --git a/src/common/sandbox.c b/src/common/sandbox.c
index 3d27ea66b507ab817f5b0606d3f52c8862b61f90..0a972d496b0702877aaeee04f22058aac6152906 100644 (file)
--- a/src/common/sandbox.c
+++ b/src/common/sandbox.c
@@ -469,7 +469,7 @@ allow_file_open(scmp_filter_ctx ctx, int use_openat, const char *file)
 {
   if (use_openat) {
     return seccomp_rule_add_2(ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat),
-                              SCMP_CMP_STR(0, SCMP_CMP_EQ, AT_FDCWD),
+                              SCMP_CMP(0, SCMP_CMP_EQ, (unsigned int)AT_FDCWD),
                               SCMP_CMP_STR(1, SCMP_CMP_EQ, file));
   } else {
     return seccomp_rule_add_1(ctx, SCMP_ACT_ALLOW, SCMP_SYS(open),