RE: [PATCH v2 0/3] fixes for udmabuf (memfd sealing checks and a leak)

Hi Jann,

Subject: [PATCH v2 0/3] fixes for udmabuf (memfd sealing checks and a leak)

I have tested that patches 2 and 3 work using the following reproducers. I did not write a reproducer for the issue described in patch 1.

Reproducer for F_SEAL_FUTURE_WRITE not being respected:

#define _GNU_SOURCE
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/udmabuf.h>

#define SYSCHK(x) ({          \
  typeof(x) __res = (x);      \
  if (__res == (typeof(x))-1) \
    err(1, "SYSCHK(" #x ")"); \
  __res;                      \
})

int main(void) {
  int memfd = SYSCHK(memfd_create("test", MFD_ALLOW_SEALING));
  SYSCHK(ftruncate(memfd, 0x1000));
  SYSCHK(fcntl(memfd, F_ADD_SEALS,
F_SEAL_SHRINK|F_SEAL_FUTURE_WRITE));
  int udmabuf_fd = SYSCHK(open("/dev/udmabuf", O_RDWR));
  struct udmabuf_create create_arg = {
    .memfd = memfd,
    .flags = 0,
    .offset = 0,
    .size = 0x1000
  };
  int buf_fd = SYSCHK(ioctl(udmabuf_fd, UDMABUF_CREATE, &create_arg));
  printf("created udmabuf buffer fd %d\n", buf_fd);
  char *map = SYSCHK(mmap(NULL, 0x1000, PROT_READ|PROT_WRITE,
MAP_SHARED, buf_fd, 0));
  *map = 'a';
}

Reproducer for the memory leak (if you run this for a while, your memory usage will steadily go up, and /sys/kernel/debug/dma_buf/bufinfo will contain a ton of entries):

#define _GNU_SOURCE
#include <err.h>
#include <errno.h>
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <linux/udmabuf.h>

#define SYSCHK(x) ({          \
  typeof(x) __res = (x);      \
  if (__res == (typeof(x))-1) \
    err(1, "SYSCHK(" #x ")"); \
  __res;                      \
})

int main(void) {
  int memfd = SYSCHK(memfd_create("test", MFD_ALLOW_SEALING));
  SYSCHK(ftruncate(memfd, 0x1000));
  SYSCHK(fcntl(memfd, F_ADD_SEALS, F_SEAL_SHRINK));
  int udmabuf_fd = SYSCHK(open("/dev/udmabuf", O_RDWR));

  // prevent creating new FDs
  struct rlimit rlim = { .rlim_cur = 1, .rlim_max = 1 };
  SYSCHK(setrlimit(RLIMIT_NOFILE, &rlim));

  while (1) {
    struct udmabuf_create create_arg = {
      .memfd = memfd,
      .flags = 0,
      .offset = 0,
      .size = 0x1000
    };
    int buf_fd = ioctl(udmabuf_fd, UDMABUF_CREATE, &create_arg);
    assert(buf_fd == -1);
    assert(errno == EMFILE);
  }
}

Signed-off-by: Jann Horn jannh@google.com

Changes in v2:

• patch 1/3: use file_inode instead of ->f_inode (Vivek)
• patch 1/3: add comment explaining the inode_lock_shared()
• patch 3/3: remove unused parameter (Vivek)
• patch 3/3: add comment on cleanup (Vivek)
• collect Acks
• Link to v1: https://lore.kernel.org/r/20241203-udmabuf-fixes-v1-0-

f99281c345aa@google.com

---

Jann Horn (3): udmabuf: fix racy memfd sealing check udmabuf: also check for F_SEAL_FUTURE_WRITE udmabuf: fix memory leak on last export_udmabuf() error path

Thank you for the fixes; all patches pushed to drm-misc-fixes.

Thanks, Vivek

drivers/dma-buf/udmabuf.c | 43 +++++++++++++++++++++++++++-------------

1 file changed, 27 insertions(+), 16 deletions(-)

base-commit: b86545e02e8c22fb89218f29d381fa8e8b91d815 change-id: 20241203-udmabuf-fixes-d0435ebab663

-- Jann Horn jannh@google.com