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SubjectRe: [PATCH 1/2] fs, elf: drop MAP_FIXED usage from elf_map
Hi Michal,

Earlier I posted a patchset to clean up these in a different way, but
patches sent to your below mail address are all rejected.

<mhocko@kerne.org>: host mail.kerne.org[104.131.33.237] said: 454 4.1.1
<mhocko@kerne.org>: Recipient address rejected: User unknown in virtual
mailbox table (in reply to RCPT TO command)

On 10/16/17 at 03:44pm, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 6466153f2bf0..09456e2add18 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -341,6 +341,29 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
>
> #ifndef elf_map
>
> +static unsigned long elf_vm_mmap(struct file *filep, unsigned long addr,
> + unsigned long size, int prot, int type, unsigned long off)
> +{
> + unsigned long map_addr;
> +
> + /*
> + * If caller requests the mapping at a specific place, make sure we fail
> + * rather than potentially clobber an existing mapping which can have
> + * security consequences (e.g. smash over the stack area).
> + */
> + map_addr = vm_mmap(filep, addr, size, prot, type & ~MAP_FIXED, off);
> + if (BAD_ADDR(map_addr))
> + return map_addr;
> +
> + if ((type & MAP_FIXED) && map_addr != addr) {
> + pr_info("Uhuuh, elf segement at %p requested but the memory is mapped already\n",
> + (void*)addr);
> + return -EAGAIN;
> + }
> +
> + return map_addr;
> +}
> +
> static unsigned long elf_map(struct file *filep, unsigned long addr,
> struct elf_phdr *eppnt, int prot, int type,
> unsigned long total_size)
> @@ -366,11 +389,11 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
> */
> if (total_size) {
> total_size = ELF_PAGEALIGN(total_size);
> - map_addr = vm_mmap(filep, addr, total_size, prot, type, off);
> + map_addr = elf_vm_mmap(filep, addr, total_size, prot, type, off);
> if (!BAD_ADDR(map_addr))
> vm_munmap(map_addr+size, total_size-size);

Here we will still take the map total, then unmap the rest way.

I am wondering why we don't fix those issues we figured out, but add
another level of wrapper elf_vm_mmap() to hack it. So we will have
elf_map() -> elf_vm_mmap() -> vm_mmap(), not even counting
vm_mmap_pgoff(), then finally enter into do_mmap_pgoff(), to do the
maping for elf program.

Thanks
Baoquan


> } else
> - map_addr = vm_mmap(filep, addr, size, prot, type, off);
> + map_addr = elf_vm_mmap(filep, addr, size, prot, type, off);
>
> return(map_addr);
> }
> @@ -1215,7 +1238,7 @@ static int load_elf_library(struct file *file)
> eppnt++;
>
> /* Now use mmap to map the library into memory. */
> - error = vm_mmap(file,
> + error = elf_vm_mmap(file,
> ELF_PAGESTART(eppnt->p_vaddr),
> (eppnt->p_filesz +
> ELF_PAGEOFFSET(eppnt->p_vaddr)),
> --
> 2.14.2
>

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