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@xxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Suggested-by: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
fs/binfmt_elf.c | 32 +++++++++++++++++++++++---------
1 file changed, 23 insertions(+), 9 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index f8b4747f87ed..22027b0a5923 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -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);
--
2.34.1
