[PATCH 1/2] x86_64: Add safe check in a.out loaders and some coding style

Geyslan G. Bem
2013-09-18T02:56:05Z

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 printk strings 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@gmail.com>
---
arch/x86/ia32/ia32_aout.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index bae3aba..15a8319 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -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
@@ -350,14 +357,13 @@ static int load_aout_binary(struct linux_binprm *bprm)
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",
+ "fd_offset is not page aligned. Please convert program: %s\n",
bprm->file->f_path.dentry->d_name.name);
error_time = jiffies;
}
#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 +430,17 @@ 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;

@@ -441,8 +454,7 @@ static int load_aout_library(struct file *file)
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",
+ "N_TXTOFF is not page aligned. Please convert library: %s\n",
file->f_path.dentry->d_name.name);
error_time = jiffies;
}
--
1.8.4