Re: [Potential Spoof] [PATCH v3] mm: memory: fix /proc/meminfo reporting for MLOCK_ONFAULT

Roman Gushchin
2019-09-13T21:18:41Z

On Fri, Sep 13, 2019 at 02:11:19PM -0700, Lucian Adrian Grijincu wrote:
> As pages are faulted in MLOCK_ONFAULT correctly updates
> /proc/self/smaps, but doesn't update /proc/meminfo's Mlocked field.
>
> - Before this /proc/meminfo fields didn't change as pages were faulted in:
>
> = Start =
> /proc/meminfo
> Unevictable: 10128 kB
> Mlocked: 10132 kB
> = Creating testfile =
>
> = after mlock2(MLOCK_ONFAULT) =
> /proc/meminfo
> Unevictable: 10128 kB
> Mlocked: 10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
> Locked: 0 kB
>
> = after reading half of the file =
> /proc/meminfo
> Unevictable: 10128 kB
> Mlocked: 10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
> Locked: 524288 kB
>
> = after reading the entire the file =
> /proc/meminfo
> Unevictable: 10128 kB
> Mlocked: 10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
> Locked: 1048576 kB
>
> = after munmap =
> /proc/meminfo
> Unevictable: 10128 kB
> Mlocked: 10132 kB
> /proc/self/smaps
>
> - After: /proc/meminfo fields are properly updated as pages are touched:
>
> = Start =
> /proc/meminfo
> Unevictable: 60 kB
> Mlocked: 60 kB
> = Creating testfile =
>
> = after mlock2(MLOCK_ONFAULT) =
> /proc/meminfo
> Unevictable: 60 kB
> Mlocked: 60 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
> Locked: 0 kB
>
> = after reading half of the file =
> /proc/meminfo
> Unevictable: 524220 kB
> Mlocked: 524220 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
> Locked: 524288 kB
>
> = after reading the entire the file =
> /proc/meminfo
> Unevictable: 1048496 kB
> Mlocked: 1048508 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
> Locked: 1048576 kB
>
> = after munmap =
> /proc/meminfo
> Unevictable: 176 kB
> Mlocked: 60 kB
> /proc/self/smaps
>
> Repro code.
> ---
>
> int mlock2wrap(const void* addr, size_t len, int flags) {
> return syscall(SYS_mlock2, addr, len, flags);
> }
>
> void smaps() {
> char smapscmd[1000];
> snprintf(
> smapscmd,
> sizeof(smapscmd) - 1,
> "grep testfile -A 20 /proc/%d/smaps | grep -E '(testfile|Locked)'",
> getpid());
> printf("/proc/self/smaps\n");
> fflush(stdout);
> system(smapscmd);
> }
>
> void meminfo() {
> const char* meminfocmd = "grep -E '(Mlocked|Unevictable)' /proc/meminfo";
> printf("/proc/meminfo\n");
> fflush(stdout);
> system(meminfocmd);
> }
>
> { \
> int rc = (call); \
> if (rc != 0) { \
> printf("error %d %s\n", rc, strerror(errno)); \
> exit(1); \
> } \
> }
> int main(int argc, char* argv[]) {
> printf("= Start =\n");
> meminfo();
>
> printf("= Creating testfile =\n");
> size_t size = 1 << 30; // 1 GiB
> int fd = open("testfile", O_CREAT | O_RDWR, 0666);
> {
> void* buf = malloc(size);
> write(fd, buf, size);
> free(buf);
> }
> int ret = 0;
> void* addr = NULL;
> addr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>
> if (argc > 1) {
> PCHECK(mlock2wrap(addr, size, MLOCK_ONFAULT));
> printf("= after mlock2(MLOCK_ONFAULT) =\n");
> meminfo();
> smaps();
>
> for (size_t i = 0; i < size / 2; i += 4096) {
> ret += ((char*)addr)[i];
> }
> printf("= after reading half of the file =\n");
> meminfo();
> smaps();
>
> for (size_t i = 0; i < size; i += 4096) {
> ret += ((char*)addr)[i];
> }
> printf("= after reading the entire the file =\n");
> meminfo();
> smaps();
>
> } else {
> PCHECK(mlock(addr, size));
> printf("= after mlock =\n");
> meminfo();
> smaps();
> }
>
> PCHECK(munmap(addr, size));
> printf("= after munmap =\n");
> meminfo();
> smaps();
>
> return ret;
> }
>
> ---
>
> Signed-off-by: Lucian Adrian Grijincu <lucian@fb.com>
> Acked-by: Souptick Joarder <jrdr.linux@gmail.com>
> ---
> mm/memory.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e0c232fe81d9..55da24f33bc4 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3311,6 +3311,8 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
> } else {
> inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
> page_add_file_rmap(page, false);
> + if (vma->vm_flags & VM_LOCKED && !PageTransCompound(page))
> + mlock_vma_page(page);

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!