Fix handling of ELF segments with zero filesize

From: David Gibson
Date: Wed Nov 30 2005 - 19:20:51 EST


Andrew, please apply

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: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>

Index: working-2.6/fs/binfmt_elf.c
===================================================================
--- working-2.6.orig/fs/binfmt_elf.c 2005-11-23 15:56:30.000000000 +1100
+++ working-2.6/fs/binfmt_elf.c 2005-12-01 11:11:01.000000000 +1100
@@ -288,11 +288,17 @@ static unsigned long elf_map(struct file
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);
}

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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