lkml.org 
[lkml]   [2013]   [Sep]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2 1/1] proc: make proc_fd_permission() thread-friendly
proc_fd_permission() says "process can still access /proc/self/fd
after it has executed a setuid()", but the "task_pid() = proc_pid()
check only helps if the task is group leader, /proc/self points to
/proc/<leader-pid>.

Change this check to use task_tgid() so that the whole thread group
can access its /proc/self/fd or /proc/<tid-of-sub-thread>/fd.

Notes:
- CLONE_THREAD does not require CLONE_FILES so task->files
can differ, but I don't think this can lead to any security
problem. And this matches same_thread_group() in
__ptrace_may_access().

- /proc/self should probably point to /proc/<thread-tid>, but
it is too late to change the rules. Perhaps it makes sense
to add /proc/thread though.


Test-case:

void *tfunc(void *arg)
{
assert(opendir("/proc/self/fd"));
return NULL;
}

int main(void)
{
pthread_t t;
pthread_create(&t, NULL, tfunc, NULL);
pthread_join(t, NULL);
return 0;
}

fails if, say, this executable is not readable and suid_dumpable = 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/proc/fd.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 0ff80f9..985ea88 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -286,7 +286,7 @@ int proc_fd_permission(struct inode *inode, int mask)
int rv = generic_permission(inode, mask);
if (rv == 0)
return 0;
- if (task_pid(current) == proc_pid(inode))
+ if (task_tgid(current) == proc_pid(inode))
rv = 0;
return rv;
}
--
1.5.5.1



\
 
 \ /
  Last update: 2013-09-11 19:41    [W:0.044 / U:0.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site