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Allow threads other than the main thread to do introspection of files in
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proc without relying on read permissions. proc_pid_follow_link() calls
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proc_fd_access_allowed() which ultimately calls __ptrace_may_access().
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Though this allows additional access to some proc files, we do not
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believe that this has any unintended security implications. However it
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probably needs to be looked at carefully.
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The original problem was a thread of a process whose permissions were
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111 couldn't open its own /proc/self/exe This was interfering with a
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special purpose debugging tool. A simple reproducer is below.:
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#include <pthread.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <errno.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#define BUFSIZE 2048
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void *thread_main(void *arg){
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char *str=(char*)arg;
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char buf[BUFSIZE];
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ssize_t len=readlink("/proc/self/exe", buf, BUFSIZE);
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if(len==-1)
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printf("/proc/self/exe in %s: %s\n", str,sys_errlist[errno]);
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else
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printf("/proc/self/exe in %s: OK\n", str);
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return 0;
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}
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int main(){
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pthread_t thread;
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int retval=pthread_create( &thread, NULL, thread_main, "thread");
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if(retval!=0)
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exit(1);
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thread_main("main");
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pthread_join(thread, NULL);
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exit(0);
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}
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Signed-off-by: Ben Woodard <woodard@redhat.com>
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Signed-off-by: Mark Grondona <mgrondona@llnl.gov>
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---
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kernel/ptrace.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/kernel/ptrace.c b/kernel/ptrace.c
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index acbd284..347c4c7 100644
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--- a/kernel/ptrace.c
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+++ b/kernel/ptrace.c
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diff -ruNp linux-3.8.4-103.fc17.noarch/kernel/ptrace.c linux-3.8.4-103.fc17.ptrace/kernel/ptrace.c
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--- linux-3.8.4-103.fc17.noarch/kernel/ptrace.c 2013-02-18 17:58:34.000000000 -0600
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+++ linux-3.8.4-103.fc17.ptrace/kernel/ptrace.c 2013-03-26 14:59:01.939396346 -0500
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@@ -234,7 +234,7 @@ static int __ptrace_may_access(struct ta
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*/
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int dumpable = 0;
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/* Don't let security modules deny introspection */
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- if (task == current)
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+ if (same_thread_group(task, current))
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return 0;
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rcu_read_lock();
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tcred = __task_cred(task);
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--
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1.8.1.4
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--
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To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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the body of a message to majordomo@vger.kernel.org
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Please read the FAQ at http://www.tux.org/lkml/
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