From d00c7b993712e4bb16d0012b35b654e40159b327 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 27 Sep 2006 01:50:19 -0700 Subject: [PATCH] [PATCH] NOMMU: Permit ptrace to ignore non-PROT_WRITE VMAs in NOMMU mode Permit ptrace to modify a section that's non-shared but is marked unwritable, such as is obtained by mapping the text segment of an ELF-FDPIC executable binary with into a binary that's being ptraced[*]. [*] Under NOMMU conditions ptrace causes read-only MAP_PRIVATE mmaps to become totally private copies because if a private mapping was actually shared then the debugging setting breakpoints in it would potentially crash other processes. This is done by using the VM_MAYWRITE flag rather than the VM_WRITE flag when deciding whether to permit a write. Without this patch a debugger can't set breakpoints in the mapped text sections of executables that are mapped read-only private, even if the mmap() syscall has taken a private copy because PT_PTRACED is set. In addition, VM_MAYREAD is used instead of VM_READ for similar reasons. Signed-off-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/nommu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/nommu.c b/mm/nommu.c index 2e140a6ae22e..829fc904de11 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1258,9 +1258,9 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in len = vma->vm_end - addr; /* only read or write mappings where it is permitted */ - if (write && vma->vm_flags & VM_WRITE) + if (write && vma->vm_flags & VM_MAYWRITE) len -= copy_to_user((void *) addr, buf, len); - else if (!write && vma->vm_flags & VM_READ) + else if (!write && vma->vm_flags & VM_MAYREAD) len -= copy_from_user(buf, (void *) addr, len); else len = 0; -- 2.20.1