proc: do not access cmdline nor environ from file-backed areas
proc_pid_cmdline_read() and environ_read() directly access the target process' VM to retrieve the command line and environment. If this process remaps these areas onto a file via mmap(), the requesting process may experience various issues such as extra delays if the underlying device is slow to respond. Let's simply refuse to access file-backed areas in these functions. For this we add a new FOLL_ANON gup flag that is passed to all calls to access_remote_vm(). The code already takes care of such failures (including unmapped areas). Accesses via /proc/pid/mem were not changed though. This was assigned CVE-2018-1120. Note for stable backports: the patch may apply to kernels prior to 4.11 but silently miss one location; it must be checked that no call to access_remote_vm() keeps zero as the last argument. Reported-by: Qualys Security Advisory <qsa@qualys.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -261,7 +261,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
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* Inherently racy -- command line shares address space
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* with code and data.
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*/
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rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0);
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rv = access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_ANON);
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if (rv <= 0)
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goto out_free_page;
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@ -279,7 +279,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
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int nr_read;
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_count = min3(count, len, PAGE_SIZE);
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nr_read = access_remote_vm(mm, p, page, _count, 0);
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nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON);
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if (nr_read < 0)
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rv = nr_read;
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if (nr_read <= 0)
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@ -325,7 +325,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
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bool final;
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_count = min3(count, len, PAGE_SIZE);
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nr_read = access_remote_vm(mm, p, page, _count, 0);
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nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON);
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if (nr_read < 0)
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rv = nr_read;
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if (nr_read <= 0)
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@ -946,7 +946,7 @@ static ssize_t environ_read(struct file *file, char __user *buf,
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max_len = min_t(size_t, PAGE_SIZE, count);
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this_len = min(max_len, this_len);
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retval = access_remote_vm(mm, (env_start + src), page, this_len, 0);
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retval = access_remote_vm(mm, (env_start + src), page, this_len, FOLL_ANON);
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if (retval <= 0) {
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ret = retval;
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@ -2493,6 +2493,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
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#define FOLL_MLOCK 0x1000 /* lock present pages */
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#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
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#define FOLL_COW 0x4000 /* internal GUP flag */
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#define FOLL_ANON 0x8000 /* don't do file mappings */
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static inline int vm_fault_to_errno(int vm_fault, int foll_flags)
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{
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3
mm/gup.c
3
mm/gup.c
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@ -544,6 +544,9 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
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if (vm_flags & (VM_IO | VM_PFNMAP))
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return -EFAULT;
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if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
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return -EFAULT;
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if (write) {
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if (!(vm_flags & VM_WRITE)) {
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if (!(gup_flags & FOLL_FORCE))
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