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Subject[PATCH] Allow either tid or pid in SCM_CREDENTIALS struct ucred
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Andrew,

Could you stick this in -mm and see if anyone complains? It fixes an
apparent bug in the validation of the SCM_CREDENTIALS structure in a
unix-domain socket sendmsg().

I found this because with Valgrind, the sendmsg call is being done in a
different thread from the one which did a getpid() to fill out the
SCM_CREDENTIALS structure, which causes the kernel to fail the sendmsg
with EPERM. In the general case, this would cause a multithreaded
program sending messages with SCM_CREDENTIALS to appear schizophrenic to
a recipient, because every message would have a different pid depending
on which thread happened to send it.
If you use SCM_CREDENTIALS with a unix domain socket, and you're
non-root, then the kernel double-checks the values you supply for pid,
uid and gid in struct ucred. In the case of uid or gid, it allows any
of effective, saved or real uid/gid. In the case of pid, it only allows
current->pid, which is actually the tid.

This patch also makes it accept tgid in the SCM_CREDENTIALS pid field.
That is, a threaded program can either supply the ID of the whole
process (tgid) or a particular thread (pid).

Thanks,
J

net/core/scm.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletion(-)
diff -puN net/core/scm.c~scm_allow_tgid net/core/scm.c
--- local-2.6/net/core/scm.c~scm_allow_tgid 2003-08-20 19:52:40.000000000 -0700
+++ local-2.6-jeremy/net/core/scm.c 2003-08-21 00:28:10.295629745 -0700
@@ -41,7 +41,8 @@

static __inline__ int scm_check_creds(struct ucred *creds)
{
- if ((creds->pid == current->pid || capable(CAP_SYS_ADMIN)) &&
+ if (((creds->pid == current->pid || creds->pid == current->tgid) ||
+ capable(CAP_SYS_ADMIN)) &&
((creds->uid == current->uid || creds->uid == current->euid ||
creds->uid == current->suid) || capable(CAP_SETUID)) &&
((creds->gid == current->gid || creds->gid == current->egid ||
_


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