Messages in this thread Patch in this message |  | | Date | Fri, 6 Apr 2018 00:03:50 +0300 | From | "Michael S. Tsirkin" <> | Subject | [PATCH v2 2/3] gup: return -EFAULT on access_ok failure |
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get_user_pages_fast is supposed to be a faster drop-in equivalent of get_user_pages. As such, callers expect it to return a negative return code when passed an invalid address, and never expect it to return 0 when passed a positive number of pages, since its documentation says:
* Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno.
When get_user_pages_fast fall back on get_user_pages this is exactly what happens. Unfortunately the implementation is inconsistent: it returns 0 if passed a kernel address, confusing callers: for example, the following is pretty common but does not appear to do the right thing with a kernel address:
ret = get_user_pages_fast(addr, 1, writeable, &page); if (ret < 0) return ret;
Change get_user_pages_fast to return -EFAULT when supplied a kernel address to make it match expectations.
All caller have been audited for consistency with the documented semantics.
Lightly tested.
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Huang Ying <ying.huang@intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thorsten Leemhuis <regressions@leemhuis.info> Cc: stable@vger.kernel.org Fixes: 5b65c4677a57 ("mm, x86/mm: Fix performance regression in get_user_pages_fast()") Reported-by: syzbot+6304bf97ef436580fede@syzkaller.appspotmail.com Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- mm/gup.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/gup.c b/mm/gup.c index 6afae32..8f3a064 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1806,9 +1806,12 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, len = (unsigned long) nr_pages << PAGE_SHIFT; end = start + len; + if (nr_pages <= 0) + return 0; + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, (void __user *)start, len))) - return 0; + return -EFAULT; if (gup_fast_permitted(start, nr_pages, write)) { local_irq_disable(); -- MST
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