[PATCH 6.1 105/451] libbpf: Fix faccessat() usage on Android

[Sasha Levin]

From: Andrii Nakryiko <andrii@xxxxxxxxxx>

[ Upstream commit ad57654053805bf9a62602aaec74cc78edb6f235 ]

Android implementation of libc errors out with -EINVAL in faccessat() if
passed AT_EACCESS ([0]), this leads to ridiculous issue with libbpf
refusing to load /sys/kernel/btf/vmlinux on Androids ([1]). Fix by
detecting Android and redefining AT_EACCESS to 0, it's equivalent on
Android.

  [0] https://android.googlesource.com/platform/bionic/+/refs/heads/android13-release/libc/bionic/faccessat.cpp#50
  [1] https://github.com/libbpf/libbpf-bootstrap/issues/250#issuecomment-1911324250

Fixes: 6a4ab8869d0b ("libbpf: Fix the case of running as non-root with capabilities")
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240126220944.2497665-1-andrii@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf_internal.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 377642ff51fce..8669f6e0f6e2f 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -17,6 +17,20 @@
 #include <unistd.h>
 #include "relo_core.h"
 
+/* Android's libc doesn't support AT_EACCESS in faccessat() implementation
+ * ([0]), and just returns -EINVAL even if file exists and is accessible.
+ * See [1] for issues caused by this.
+ *
+ * So just redefine it to 0 on Android.
+ *
+ * [0] https://android.googlesource.com/platform/bionic/+/refs/heads/android13-release/libc/bionic/faccessat.cpp#50
+ * [1] https://github.com/libbpf/libbpf-bootstrap/issues/250#issuecomment-1911324250
+ */
+#ifdef __ANDROID__
+#undef AT_EACCESS
+#define AT_EACCESS 0
+#endif
+
 /* make sure libbpf doesn't use kernel-only integer typedefs */
 #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
 
-- 
2.43.0