Messages in this thread Patch in this message | | | Date | Wed, 11 Sep 2013 19:14:03 +0200 | From | Oleg Nesterov <> | Subject | [PATCH v2 1/1] proc: make proc_fd_permission() thread-friendly |
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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
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