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Message-ID: <CAGG-pUTEWNi2m+wej1wYDprs=8aGO5Z2szdc+E6Gw51HK98ExA@mail.gmail.com>
Date: Wed, 18 Sep 2013 20:15:38 -0300
From: Geyslan Gregório Bem <geyslan@...il.com>
To: viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, "Geyslan G. Bem" <geyslan@...il.com>
Subject: Re: [PATCH 2/2] x86_64: Add safe check in a.out loaders and some
coding style
Now it's ok.
Geyslan Gregório Bem
hackingbits.com
2013/9/18 Geyslan G. Bem <geyslan@...il.com>:
> ia32_aout had no safe checks concerning the mmap and f_op in this module.
> It's not necessary to verify f_op in the load_aout_library, since the
> prior kernel_read/vfs_read function already does.
> Coding style and printks fixes.
>
> Tested using qemu, a handcrafted a.out binary and a a.out linked with a
> cross-compiled ld.
>
> Signed-off-by: Geyslan G. Bem <geyslan@...il.com>
> ---
> arch/x86/ia32/ia32_aout.c | 51 +++++++++++++++++++++++------------------------
> 1 file changed, 25 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
> index bae3aba..a5f3e66 100644
> --- a/arch/x86/ia32/ia32_aout.c
> +++ b/arch/x86/ia32/ia32_aout.c
> @@ -24,7 +24,7 @@
> #include <linux/binfmts.h>
> #include <linux/personality.h>
> #include <linux/init.h>
> -#include <linux/jiffies.h>
> +#include <linux/ratelimit.h>
>
> #include <asm/uaccess.h>
> #include <asm/pgalloc.h>
> @@ -271,10 +271,17 @@ static int load_aout_binary(struct linux_binprm *bprm)
> N_MAGIC(ex) != QMAGIC && N_MAGIC(ex) != NMAGIC) ||
> N_TRSIZE(ex) || N_DRSIZE(ex) ||
> i_size_read(file_inode(bprm->file)) <
> - ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
> + ex.a_text + ex.a_data + N_SYMSIZE(ex) + N_TXTOFF(ex)) {
> return -ENOEXEC;
> }
>
> + /*
> + * Requires a mmap handler. This prevents people from using a.out
> + * as part of an exploit attack against /proc-related vulnerabilities.
> + */
> + if (!bprm->file->f_op || !bprm->file->f_op->mmap)
> + return -ENOEXEC;
> +
> fd_offset = N_TXTOFF(ex);
>
> /* Check initial limits. This avoids letting people circumvent
> @@ -339,25 +346,16 @@ static int load_aout_binary(struct linux_binprm *bprm)
> }
> } else {
> #ifdef WARN_OLD
> - static unsigned long error_time, error_time2;
> if ((ex.a_text & 0xfff || ex.a_data & 0xfff) &&
> - (N_MAGIC(ex) != NMAGIC) &&
> - time_after(jiffies, error_time2 + 5*HZ)) {
> - printk(KERN_NOTICE "executable not page aligned\n");
> - error_time2 = jiffies;
> - }
> + (N_MAGIC(ex) != NMAGIC))
> + pr_notice_ratelimited("executable not page aligned\n");
>
> - if ((fd_offset & ~PAGE_MASK) != 0 &&
> - time_after(jiffies, error_time + 5*HZ)) {
> - printk(KERN_WARNING
> - "fd_offset is not page aligned. Please convert "
> - "program: %s\n",
> - bprm->file->f_path.dentry->d_name.name);
> - error_time = jiffies;
> - }
> + if ((fd_offset & ~PAGE_MASK) != 0)
> + pr_warn_ratelimited("fd_offset is not page aligned. Please convert program: %s\n",
> + bprm->file->f_path.dentry->d_name.name);
> #endif
>
> - if (!bprm->file->f_op->mmap || (fd_offset & ~PAGE_MASK) != 0) {
> + if ((fd_offset & ~PAGE_MASK) != 0) {
> vm_brk(N_TXTADDR(ex), ex.a_text+ex.a_data);
> read_code(bprm->file, N_TXTADDR(ex), fd_offset,
> ex.a_text+ex.a_data);
> @@ -424,10 +422,17 @@ static int load_aout_library(struct file *file)
> if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != QMAGIC) || N_TRSIZE(ex) ||
> N_DRSIZE(ex) || ((ex.a_entry & 0xfff) && N_MAGIC(ex) == ZMAGIC) ||
> i_size_read(file_inode(file)) <
> - ex.a_text+ex.a_data+N_SYMSIZE(ex)+N_TXTOFF(ex)) {
> + ex.a_text + ex.a_data + N_SYMSIZE(ex) + N_TXTOFF(ex)) {
> goto out;
> }
>
> + /*
> + * Requires a mmap handler. This prevents people from using a.out
> + * as part of an exploit attack against /proc-related vulnerabilities.
> + */
> + if (!file->f_op->mmap)
> + goto out;
> +
> if (N_FLAGS(ex))
> goto out;
>
> @@ -438,14 +443,8 @@ static int load_aout_library(struct file *file)
>
> if ((N_TXTOFF(ex) & ~PAGE_MASK) != 0) {
> #ifdef WARN_OLD
> - static unsigned long error_time;
> - if (time_after(jiffies, error_time + 5*HZ)) {
> - printk(KERN_WARNING
> - "N_TXTOFF is not page aligned. Please convert "
> - "library: %s\n",
> - file->f_path.dentry->d_name.name);
> - error_time = jiffies;
> - }
> + pr_warn_ratelimited("N_TXTOFF is not page aligned. Please convert library: %s\n",
> + file->f_path.dentry->d_name.name);
> #endif
> vm_brk(start_addr, ex.a_text + ex.a_data + ex.a_bss);
>
> --
> 1.8.4
>
--
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