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binfmt_elf: Only report padzero() errors when PROT_WRITE

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Errors with padzero() should be caught unless we're expecting a
pathological (non-writable) segment. Report -EFAULT only when PROT_WRITE
is present.

Additionally add some more documentation to padzero(), elf_map(), and
elf_load().

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Suggested-by: Eric Biederman <ebiederm@xmission.com>
Tested-by: Pedro Falcato <pedro.falcato@gmail.com>
Signed-off-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20230929032435.2391507-5-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2023-09-28 20:24:33 -07:00
parent d5ca24f639
commit f9c0a39d95
1 changed files with 23 additions and 9 deletions
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32
fs/binfmt_elf.c
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@ -110,19 +110,19 @@ static struct linux_binfmt elf_format = {
#define BAD_ADDR(x) (unlikely((unsigned long)(x) >= TASK_SIZE))
/* We need to explicitly zero any fractional pages
after the data section (i.e. bss). This would
contain the junk from the file that should not
be in memory
/*
* We need to explicitly zero any trailing portion of the page that follows
* p_filesz when it ends before the page ends (e.g. bss), otherwise this
* memory will contain the junk from the file that should not be present.
*/
static int padzero(unsigned long elf_bss)
static int padzero(unsigned long address)
{
unsigned long nbyte;
nbyte = ELF_PAGEOFFSET(elf_bss);
nbyte = ELF_PAGEOFFSET(address);
if (nbyte) {
nbyte = ELF_MIN_ALIGN - nbyte;
if (clear_user((void __user *) elf_bss, nbyte))
if (clear_user((void __user *)address, nbyte))
return -EFAULT;
}
return 0;
@ -348,6 +348,11 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
return 0;
}
/*
* Map "eppnt->p_filesz" bytes from "filep" offset "eppnt->p_offset"
* into memory at "addr". (Note that p_filesz is rounded up to the
* next page, so any extra bytes from the file must be wiped.)
*/
static unsigned long elf_map(struct file *filep, unsigned long addr,
const struct elf_phdr *eppnt, int prot, int type,
unsigned long total_size)
@ -387,6 +392,11 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
return(map_addr);
}
/*
* Map "eppnt->p_filesz" bytes from "filep" offset "eppnt->p_offset"
* into memory at "addr". Memory from "p_filesz" through "p_memsz"
* rounded up to the next page is zeroed.
*/
static unsigned long elf_load(struct file *filep, unsigned long addr,
const struct elf_phdr *eppnt, int prot, int type,
unsigned long total_size)
@ -404,8 +414,12 @@ static unsigned long elf_load(struct file *filep, unsigned long addr,
zero_end = map_addr + ELF_PAGEOFFSET(eppnt->p_vaddr) +
eppnt->p_memsz;
/* Zero the end of the last mapped page */
padzero(zero_start);
/*
* Zero the end of the last mapped page but ignore
* any errors if the segment isn't writable.
*/
if (padzero(zero_start) && (prot & PROT_WRITE))
return -EFAULT;
}
} else {
map_addr = zero_start = ELF_PAGESTART(addr);