From 2f77d107050abc14bc393b34bdb7b91cf670c250 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Dec 2006 09:44:32 -0800 Subject: Fix incorrect user space access locking in mincore() Doug Chapman noticed that mincore() will doa "copy_to_user()" of the result while holding the mmap semaphore for reading, which is a big no-no. While a recursive read-lock on a semaphore in the case of a page fault happens to work, we don't actually allow them due to deadlock schenarios with writers due to fairness issues. Doug and Marcel sent in a patch to fix it, but I decided to just rewrite the mess instead - not just fixing the locking problem, but making the code smaller and (imho) much easier to understand. Cc: Doug Chapman Cc: Marcel Holtmann Cc: Hugh Dickins Cc: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mincore.c | 190 +++++++++++++++++++++++++++-------------------------------- 1 file changed, 86 insertions(+), 104 deletions(-) (limited to 'mm') diff --git a/mm/mincore.c b/mm/mincore.c index 72890780c1..b44d7f875c 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -1,7 +1,7 @@ /* * linux/mm/mincore.c * - * Copyright (C) 1994-1999 Linus Torvalds + * Copyright (C) 1994-2006 Linus Torvalds */ /* @@ -38,46 +38,60 @@ static unsigned char mincore_page(struct vm_area_struct * vma, return present; } -static long mincore_vma(struct vm_area_struct * vma, - unsigned long start, unsigned long end, unsigned char __user * vec) +/* + * Do a chunk of "sys_mincore()". We've already checked + * all the arguments, we hold the mmap semaphore: we should + * just return the amount of info we're asked for. + */ +static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pages) { - long error, i, remaining; - unsigned char * tmp; + unsigned long i, nr, pgoff; + struct vm_area_struct *vma = find_vma(current->mm, addr); - error = -ENOMEM; - if (!vma->vm_file) - return error; - - start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; - if (end > vma->vm_end) - end = vma->vm_end; - end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; + /* + * find_vma() didn't find anything: the address + * is above everything we have mapped. + */ + if (!vma) { + memset(vec, 0, pages); + return pages; + } - error = -EAGAIN; - tmp = (unsigned char *) __get_free_page(GFP_KERNEL); - if (!tmp) - return error; + /* + * find_vma() found something, but we might be + * below it: check for that. + */ + if (addr < vma->vm_start) { + unsigned long gap = (vma->vm_start - addr) >> PAGE_SHIFT; + if (gap > pages) + gap = pages; + memset(vec, 0, gap); + return gap; + } - /* (end - start) is # of pages, and also # of bytes in "vec */ - remaining = (end - start), + /* + * Ok, got it. But check whether it's a segment we support + * mincore() on. Right now, we don't do any anonymous mappings. + */ + if (!vma->vm_file) + return -ENOMEM; - error = 0; - for (i = 0; remaining > 0; remaining -= PAGE_SIZE, i++) { - int j = 0; - long thispiece = (remaining < PAGE_SIZE) ? - remaining : PAGE_SIZE; + /* + * Calculate how many pages there are left in the vma, and + * what the pgoff is for our address. + */ + nr = (vma->vm_end - addr) >> PAGE_SHIFT; + if (nr > pages) + nr = pages; - while (j < thispiece) - tmp[j++] = mincore_page(vma, start++); + pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; + pgoff += vma->vm_pgoff; - if (copy_to_user(vec + PAGE_SIZE * i, tmp, thispiece)) { - error = -EFAULT; - break; - } - } + /* And then we just fill the sucker in.. */ + for (i = 0 ; i < nr; i++, pgoff++) + vec[i] = mincore_page(vma, pgoff); - free_page((unsigned long) tmp); - return error; + return nr; } /* @@ -107,82 +121,50 @@ static long mincore_vma(struct vm_area_struct * vma, asmlinkage long sys_mincore(unsigned long start, size_t len, unsigned char __user * vec) { - int index = 0; - unsigned long end, limit; - struct vm_area_struct * vma; - size_t max; - int unmapped_error = 0; - long error; - - /* check the arguments */ - if (start & ~PAGE_CACHE_MASK) - goto einval; - - limit = TASK_SIZE; - if (start >= limit) - goto enomem; - - if (!len) - return 0; + long retval; + unsigned long pages; + unsigned char *tmp; - max = limit - start; - len = PAGE_CACHE_ALIGN(len); - if (len > max || !len) - goto enomem; - - end = start + len; + /* Check the start address: needs to be page-aligned.. */ + if (start & ~PAGE_CACHE_MASK) + return -EINVAL; - /* check the output buffer whilst holding the lock */ - error = -EFAULT; - down_read(¤t->mm->mmap_sem); + /* ..and we need to be passed a valid user-space range */ + if (!access_ok(VERIFY_READ, (void __user *) start, len)) + return -ENOMEM; - if (!access_ok(VERIFY_WRITE, vec, len >> PAGE_SHIFT)) - goto out; + /* This also avoids any overflows on PAGE_CACHE_ALIGN */ + pages = len >> PAGE_SHIFT; + pages += (len & ~PAGE_MASK) != 0; - /* - * If the interval [start,end) covers some unmapped address - * ranges, just ignore them, but return -ENOMEM at the end. - */ - error = 0; - - vma = find_vma(current->mm, start); - while (vma) { - /* Here start < vma->vm_end. */ - if (start < vma->vm_start) { - unmapped_error = -ENOMEM; - start = vma->vm_start; - } + if (!access_ok(VERIFY_WRITE, vec, pages)) + return -EFAULT; - /* Here vma->vm_start <= start < vma->vm_end. */ - if (end <= vma->vm_end) { - if (start < end) { - error = mincore_vma(vma, start, end, - &vec[index]); - if (error) - goto out; - } - error = unmapped_error; - goto out; + tmp = (void *) __get_free_page(GFP_USER); + if (!tmp) + return -ENOMEM; + + retval = 0; + while (pages) { + /* + * Do at most PAGE_SIZE entries per iteration, due to + * the temporary buffer size. + */ + down_read(¤t->mm->mmap_sem); + retval = do_mincore(start, tmp, max(pages, PAGE_SIZE)); + up_read(¤t->mm->mmap_sem); + + if (retval <= 0) + break; + if (copy_to_user(vec, tmp, retval)) { + retval = -EFAULT; + break; } - - /* Here vma->vm_start <= start < vma->vm_end < end. */ - error = mincore_vma(vma, start, vma->vm_end, &vec[index]); - if (error) - goto out; - index += (vma->vm_end - start) >> PAGE_CACHE_SHIFT; - start = vma->vm_end; - vma = vma->vm_next; + pages -= retval; + vec += retval; + start += retval << PAGE_SHIFT; + retval = 0; } - - /* we found a hole in the area queried if we arrive here */ - error = -ENOMEM; - -out: - up_read(¤t->mm->mmap_sem); - return error; - -einval: - return -EINVAL; -enomem: - return -ENOMEM; + free_page((unsigned long) tmp); + return retval; } -- cgit v1.2.2 From 4fb23e439ce09157d64b89a21061b9fc08f2b495 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Dec 2006 16:01:50 -0800 Subject: Fix up mm/mincore.c error value cases Hugh Dickins correctly points out that mincore() is actually _supposed_ to fail on an unmapped hole in the user address space, rather than return valid ("empty") information about the hole. This just simplifies the problem further (I had been misled by our previous confusing and complicated way of doing mincore()). Also, in the unlikely situation that we can't allocate a temporary kernel buffer, we should actually return EAGAIN, not ENOMEM, to keep the "unmapped hole" and "allocation failure" error cases separate. Finally, add a comment about our stupid historical lack of support for anonymous mappings. I'll fix that if somebody reminds me after 2.6.20 is out. Acked-by: Hugh Dickins Signed-off-by: Linus Torvalds --- mm/mincore.c | 29 ++++++++++------------------- 1 file changed, 10 insertions(+), 19 deletions(-) (limited to 'mm') diff --git a/mm/mincore.c b/mm/mincore.c index b44d7f875c..566b6c2bae 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -49,29 +49,20 @@ static long do_mincore(unsigned long addr, unsigned char *vec, unsigned long pag struct vm_area_struct *vma = find_vma(current->mm, addr); /* - * find_vma() didn't find anything: the address - * is above everything we have mapped. + * find_vma() didn't find anything above us, or we're + * in an unmapped hole in the address space: ENOMEM. */ - if (!vma) { - memset(vec, 0, pages); - return pages; - } - - /* - * find_vma() found something, but we might be - * below it: check for that. - */ - if (addr < vma->vm_start) { - unsigned long gap = (vma->vm_start - addr) >> PAGE_SHIFT; - if (gap > pages) - gap = pages; - memset(vec, 0, gap); - return gap; - } + if (!vma || addr < vma->vm_start) + return -ENOMEM; /* * Ok, got it. But check whether it's a segment we support * mincore() on. Right now, we don't do any anonymous mappings. + * + * FIXME: This is just stupid. And returning ENOMEM is + * stupid too. We should just look at the page tables. But + * this is what we've traditionally done, so we'll just + * continue doing it. */ if (!vma->vm_file) return -ENOMEM; @@ -142,7 +133,7 @@ asmlinkage long sys_mincore(unsigned long start, size_t len, tmp = (void *) __get_free_page(GFP_USER); if (!tmp) - return -ENOMEM; + return -EAGAIN; retval = 0; while (pages) { -- cgit v1.2.2 From 825020c3866e7312947e17a0caa9dd1a5622bafc Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Sun, 17 Dec 2006 18:52:47 +0300 Subject: [PATCH] sys_mincore: s/max/min/ fix a typo, sys_mincore() needs min(). Signed-off-by: Oleg Nesterov Signed-off-by: Linus "I'm a moron" Torvalds --- mm/mincore.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/mincore.c b/mm/mincore.c index 566b6c2bae..8aca6f7167 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -142,7 +142,7 @@ asmlinkage long sys_mincore(unsigned long start, size_t len, * the temporary buffer size. */ down_read(¤t->mm->mmap_sem); - retval = do_mincore(start, tmp, max(pages, PAGE_SIZE)); + retval = do_mincore(start, tmp, min(pages, PAGE_SIZE)); up_read(¤t->mm->mmap_sem); if (retval <= 0) -- cgit v1.2.2