Follow-up Comment #4, bug #66522 (group screen): @anaumov thank you for your reply (previously annonymously)
As you suggested I did the following:
git checkout screen-v5
# now at 1ef836308b8d7c8f0259dc62756b1b19fe82db4b
git revert d10eb5b2f7eebaa347f09c010bd391373fdd1695
After building and testing I got:
seteuid: Operation not permitted
[...]
seteuid: Operation not permitted
seteuid: Operation not permitted
Segmentation fault (core dumped) screen -x user/screenid
Independently of your suggestion, we at Aachner Linux User Group found the
following output in strace:
setresuid(1000, 0, 1000) = 0
setresuid(-1, 1000, -1) = 0
setresgid(-1, 0, -1) = 0
openat(AT_FDCWD, "/home/hinrikus/.screen",
O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
fstat(3, {st_mode=S_IFDIR|0700, st_size=4096, ...}) = 0
getdents64(3, 0x560263ddfeb0 /* 3 entries */, 32768) = 96
newfstatat(AT_FDCWD, "/home/hinrikus/.screen/608506.pts-8.redacted",
{st_mode=S_IFSOCK|0701, st_size=0, ...}, 0) = 0
socket(AF_UNIX, SOCK_STREAM, 0) = 4
setresuid(-1, 1000, -1) = 0
setresgid(-1, 0, -1) = 0
connect(4, {sa_family=AF_UNIX,
sun_path="/home/hinrikus/.screen/608506.pts-8.redacted"}, 48) = 0
setresuid(-1, 0, -1) = -1 EPERM (Operation not permitted)
setresuid(-1, 0, -1) = -1 EPERM (Operation not permitted)
After this we came up with the following fix on
commit: 464c8d8f945f53f8cbb854517279349e09d74756
diff --git a/src/attacher.c b/src/attacher.c
index f2b60f0..fc171b8 100644
--- a/src/attacher.c
+++ b/src/attacher.c
@@ -121,7 +121,7 @@ int Attach(int how)
real_uid = multi_uid;
eff_uid = own_uid;
#ifdef HAVE_SETRESUID
- if (setresuid(multi_uid, own_uid, multi_uid))
+ if (setresuid(multi_uid, own_uid, eff_uid))
Panic(errno, "setresuid");
#else
xseteuid(multi_uid);
This worked for me, as we did not drop the saved root uid.
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