[PATCH] Fix handling of ELF segments with zero filesize

mmap() returns -EINVAL if given a zero length, and thus elf_map() in
binfmt_elf.c does likewise if it attempts to map a (page-aligned) ELF
segment with zero filesize.  Such a situation never arises with the default
linker scripts, but there's nothing inherently wrong with zero-filesize
(but non-zero memsize) ELF segments.  Custom linker scripts can generate
them, and the kernel should be able to map them; this patch makes it so.
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/binfmt_elf.c

@@ -288,11 +288,17 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
 			struct elf_phdr *eppnt, int prot, int type)
 {
 	unsigned long map_addr;
+	unsigned long pageoffset = ELF_PAGEOFFSET(eppnt->p_vaddr);
 
 	down_write(&current->mm->mmap_sem);
-	map_addr = do_mmap(filep, ELF_PAGESTART(addr),
-			   eppnt->p_filesz + ELF_PAGEOFFSET(eppnt->p_vaddr), prot, type,
-			   eppnt->p_offset - ELF_PAGEOFFSET(eppnt->p_vaddr));
+	/* mmap() will return -EINVAL if given a zero size, but a
+	 * segment with zero filesize is perfectly valid */
+	if (eppnt->p_filesz + pageoffset)
+		map_addr = do_mmap(filep, ELF_PAGESTART(addr),
+				   eppnt->p_filesz + pageoffset, prot, type,
+				   eppnt->p_offset - pageoffset);
+	else
+		map_addr = ELF_PAGESTART(addr);
 	up_write(&current->mm->mmap_sem);
 	return(map_addr);
 }