Re: [RFC PATCH v14 05/10] fs, landlock: Support filesystem access-control

On Mon, Feb 24, 2020 at 5:03 PM Mickaël Salaün mic@digikod.net wrote:

+static inline u32 get_mem_access(unsigned long prot, bool private) +{

•   u32 access = LANDLOCK_ACCESS_FS_MAP;
  

•   /* Private mapping do not write to files. */
  

•   if (!private && (prot & PROT_WRITE))
  

•           access |= LANDLOCK_ACCESS_FS_WRITE;
  

•   if (prot & PROT_READ)
  

•           access |= LANDLOCK_ACCESS_FS_READ;
  

•   if (prot & PROT_EXEC)
  

•           access |= LANDLOCK_ACCESS_FS_EXECUTE;
  

•   return access;
  

+}

When I do the following, is landlock going to detect that the mmap() is a read access, or is it incorrectly going to think that it's neither read nor write?

$ cat write-only.c #include <fcntl.h> #include <sys/mman.h> #include <stdio.h> int main(void) { int fd = open("/etc/passwd", O_RDONLY); char *ptr = mmap(NULL, 0x1000, PROT_WRITE, MAP_PRIVATE, fd, 0); printf("'%.*s'\n", 4, ptr); } $ gcc -o write-only write-only.c -Wall $ ./write-only 'root' $