proc: do not access cmdline nor environ from file-backed areas

commit 7f7ccc2ccc2e70c6054685f5e3522efa81556830 upstream.

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 4.4:
 - Update the extra call to access_remote_vm() from proc_pid_cmdline_read()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5b8d840..bd8c26a 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -254,7 +254,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
         * Inherently racy -- command line shares address space
         * with code and data.
         */
-       rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0);
+       rv = access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_ANON);
        if (rv <= 0)
                goto out_free_page;
 
@@ -272,7 +272,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                        int nr_read;
 
                        _count = min3(count, len, PAGE_SIZE);
-                       nr_read = access_remote_vm(mm, p, page, _count, 0);
+                       nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON);
                        if (nr_read < 0)
                                rv = nr_read;
                        if (nr_read <= 0)
@@ -307,7 +307,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
                        bool final;
 
                        _count = min3(count, len, PAGE_SIZE);
-                       nr_read = access_remote_vm(mm, p, page, _count, 0);
+                       nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON);
                        if (nr_read < 0)
                                rv = nr_read;
                        if (nr_read <= 0)
@@ -356,7 +356,7 @@ skip_argv:
                        bool final;
 
                        _count = min3(count, len, PAGE_SIZE);
-                       nr_read = access_remote_vm(mm, p, page, _count, 0);
+                       nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON);
                        if (nr_read < 0)
                                rv = nr_read;
                        if (nr_read <= 0)
@@ -1006,7 +1006,7 @@ static ssize_t environ_read(struct file *file, char __user *buf,
                max_len = min_t(size_t, PAGE_SIZE, count);
                this_len = min(max_len, this_len);
 
-               retval = access_remote_vm(mm, (env_start + src), page, this_len, 0);
+               retval = access_remote_vm(mm, (env_start + src), page, this_len, FOLL_ANON);
 
                if (retval <= 0) {
                        ret = retval;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9a0716e..251adf4 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2120,6 +2120,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
 #define FOLL_TRIED     0x800   /* a retry, previous pass started an IO */
 #define FOLL_MLOCK     0x1000  /* lock present pages */
 #define FOLL_COW       0x4000  /* internal GUP flag */
+#define FOLL_ANON      0x8000  /* don't do file mappings */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
                        void *data);

diff --git a/mm/gup.c b/mm/gup.c
index 2370e24..2cd3b31 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -368,6 +368,9 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
        if (vm_flags & (VM_IO | VM_PFNMAP))
                return -EFAULT;
 
+       if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
+               return -EFAULT;
+
        if (gup_flags & FOLL_WRITE) {
                if (!(vm_flags & VM_WRITE)) {
                        if (!(gup_flags & FOLL_FORCE))