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Fix the following race:

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1. Process p1 is currently being swapped in.
  2. Process p2 calls linux_ptrace(PTRACE_GETFPXREGS, p1_pid, ...)
  3. After acquiring a reference to FIRST_THREAD_IN_PROC(p1),
     p2 blocks in faultin() while p1 finishes being swapped in.
     This means p2 won't get back the lock on p1 until after p1's
     threads are runnable.
  4. After p1 is swapped in, the first thread in p1 exits.
  5. p2 now uses its dangling reference to p1's first thread.
This commit is contained in:
David Schultz 2004-10-01 05:01:00 +00:00
parent 9648e4c416
commit 46ec41ecb4
1 changed files with 4 additions and 3 deletions
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7
sys/i386/linux/linux_ptrace.c
View file

@ -386,9 +386,9 @@ linux_ptrace(struct thread *td, struct linux_ptrace_args *uap)
goto fail;
}
td2 = FIRST_THREAD_IN_PROC(p);
if (req == PTRACE_GETFPXREGS) {
_PHOLD(p);
_PHOLD(p); /* may block */
td2 = FIRST_THREAD_IN_PROC(p);
error = linux_proc_read_fpxregs(td2, &r.fpxreg);
_PRELE(p);
PROC_UNLOCK(p);
@ -398,7 +398,8 @@ linux_ptrace(struct thread *td, struct linux_ptrace_args *uap)
} else {
/* clear dangerous bits exactly as Linux does*/
r.fpxreg.mxcsr &= 0xffbf;
_PHOLD(p);
_PHOLD(p); /* may block */
td2 = FIRST_THREAD_IN_PROC(p);
error = linux_proc_write_fpxregs(td2, &r.fpxreg);
_PRELE(p);
PROC_UNLOCK(p);