binfmt_elf: remove the set_fs(KERNEL_DS) in elf_core_dump

There is no logic in elf_core_dump itself or in the various arch helpers
called from it which use uaccess routines on kernel pointers except for
the file writes thate are nicely encapsulated by using __kernel_write in
dump_emit.

Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Al Viro <[email protected]>

Author: Christoph Hellwig

fs/binfmt_elf.c

@@ -1355,7 +1355,6 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma,
 	    vma->vm_pgoff == 0 && (vma->vm_flags & VM_READ)) {
 		u32 __user *header = (u32 __user *) vma->vm_start;
 		u32 word;
-		mm_segment_t fs = get_fs();
 		/*
 		 * Doing it this way gets the constant folded by GCC.
 		 */
@@ -1368,14 +1367,8 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma,
 		magic.elfmag[EI_MAG1] = ELFMAG1;
 		magic.elfmag[EI_MAG2] = ELFMAG2;
 		magic.elfmag[EI_MAG3] = ELFMAG3;
-		/*
-		 * Switch to the user "segment" for get_user(),
-		 * then put back what elf_core_dump() had in place.
-		 */
-		set_fs(USER_DS);
 		if (unlikely(get_user(word, header)))
 			word = 0;
-		set_fs(fs);
 		if (word == magic.cmp)
 			return PAGE_SIZE;
 	}
@@ -2183,7 +2176,6 @@ static void fill_extnum_info(struct elfhdr *elf, struct elf_shdr *shdr4extnum,
 static int elf_core_dump(struct coredump_params *cprm)
 {
 	int has_dumped = 0;
-	mm_segment_t fs;
 	int segs, i;
 	size_t vma_data_size = 0;
 	struct vm_area_struct *vma, *gate_vma;
@@ -2232,13 +2224,10 @@ static int elf_core_dump(struct coredump_params *cprm)
 	 * notes.  This also sets up the file header.
 	 */
 	if (!fill_note_info(&elf, e_phnum, &info, cprm->siginfo, cprm->regs))
-		goto cleanup;
+		goto end_coredump;
 
 	has_dumped = 1;
 
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-
 	offset += sizeof(elf);				/* Elf header */
 	offset += segs * sizeof(struct elf_phdr);	/* Program headers */
 
@@ -2366,9 +2355,6 @@ static int elf_core_dump(struct coredump_params *cprm)
 	}
 
 end_coredump:
-	set_fs(fs);
-
-cleanup:
 	free_note_info(&info);
 	kfree(shdr4extnum);
 	kvfree(vma_filesz);