[release-branch.go1.18] syscall: check correct group in Faccessat

The Faccessat call checks the user, group, or other permission bits of a
file to see if the calling process can access it. The test to see if the
group permissions should be used was made with the wrong group id, using
the process's group id rather than the file's group id. Fix this to use
the correct group id.

No test since we cannot easily change file permissions when not running
as root and the test is meaningless if running as root.

For #52313
Fixes #52440

Change-Id: I4e2c84754b0af7830b40fd15dedcbc58374d75ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/399539
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit f66925e854e71e0c54b581885380a490d7afa30c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/401079
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Tatiana Bradley <tatiana@golang.org>
Run-TryBot: Tatiana Bradley <tatiana@golang.org>
Auto-Submit: Tatiana Bradley <tatiana@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>

diff --git a/src/syscall/syscall_linux.go b/src/syscall/syscall_linux.go
index e3891b08558e86c90a49b84479d9b6c6ea5d454e..f32020ca6ceb39891e1fa3540efc617e71536c7b 100644 (file)
--- a/src/syscall/syscall_linux.go
+++ b/src/syscall/syscall_linux.go
@@ -109,7 +109,7 @@ func Faccessat(dirfd int, path string, mode uint32, flags int) (err error) {
                        gid = Getgid()
                }
 
-               if uint32(gid) == st.Gid || isGroupMember(gid) {
+               if uint32(gid) == st.Gid || isGroupMember(int(st.Gid)) {
                        fmode = (st.Mode >> 3) & 7
                } else {
                        fmode = st.Mode & 7